Ahmad Adi, MD

• Department of Cardiothoracic Anesthesiology
• Cleveland Clinic
• Cleveland, Ohio

If the rat had sampled all the foods at once androgen hormone blocker purchase rogaine 2 60 ml with visa, it would have had no basis for knowing which one had affected its health prostate definition buy rogaine 2 in united states online. It would not be ethical to deprive people of necessary nutrients for the sake of such research prostate psa best order for rogaine 2. However mens health january 2014 discount rogaine 2 on line, there is evidence that people mens health challenge 60 ml rogaine 2 mastercard, as well as rats androgen hormone production quality rogaine 2 60ml, learn to prefer a food that is high in calories (Brunstrom, 2005). This learning mechanism, which was no doubt valuable both to our evolutionary ancestors and to some people today, may have an unfortunate effect on those of us who are overweight and surrounded by wide choices of foods. In the typical human flavor-preference learning experiment, college students are presented each day with one of two differently flavored foods, which is either laced with a high-calorie substance or not so laced. Apparently some delayed satisfying effect of the calories causes the students to develop a preference for the high-calorie version. This may be no news to people trying to lose weight, who are already convinced that all of human nature is stacked against them. Learning from Others What to Eat In addition to learning from their own experiences with foods, rats learn what to eat from one another. Newly weaned wild rats generally limit their diets to foods that older rats in the colony regularly eat. Through this means, they can avoid even tasting a food that older animals have learned is poisonous (Galef & Clark, 1971) and can choose, from the beginning, a nutritious food that older animals have learned to prefer (Beck & Galef, 1989). In one experiment, children between 1 and 4 years old were more willing to taste a new food if they saw an adult eat it fi rst than if they had never seen anyone eat it (Harper & Sanders, 1975). Other research suggests that children are most open to new Observational learning has its limits Children acquire the food foods from about 1 to 2 years of age, which is when they preferences of their culture by observing their elders, but sometimes are most likely to be closely watched and fed by adults, it takes a while. From this point of view, the fi nicky eating of 4- to 8-year-olds is an evolutionary adaptation that reduces the chance of eating something poisonous. However, even fi nicky eaters in this age range can be rewarded with stickers to try new foods, including vegetables, and can develop a liking for the new foods that will last at least 3 months after rewards have been stopped (Cook et al. For example, in one experiment pregnant women ate anise-flavored food while others did not. Summary of Rules for Learning What to Eat Suppose that you were a wise teacher of young omnivorous animals and wanted to equip your charges with a few rules for food selection that could be applied no matter what food was available. Two that you would probably come up with are these: (1) When possible, eat what your elders eat. Such food is probably safe, as evidenced by the fact that your elders have most likely been eating it for some time and are still alive. If the food is followed within a few hours by feelings of improved health, continue choosing foods of that taste and smell, but if you feel sick, avoid such foods. Notice that these rules do not specify what to eat, but specify how to learn what to eat. The first rule describes a specific variety of observational learning, and the second describes a specific, efficient variety of associative learning. As you have just seen, rats do in fact behave in accordance with these rules, and humans may also. Of course, we assume that these rules have been imparted not by a wise teacher of young omnivores but by natural selection, which has shaped the brain to operate automatically in accordance with the rules. Other Examples of Special Learning Abilities Food selection is by no means the only domain in which special learning abilities have apparently come about through evolution. Prepared Fear-Related Learning Do you remember the demonstration by Watson and Rayner (1920), in which a young child was conditioned to fear a white rat by pairing it with a loud noise Several years later, a graduate student working with Thorndike named Elsie Bregman (1934) tried to repeat that demonstration with one important modification. Instead of using a rat as the conditioned stimulus, she used various inanimate objects, including wooden blocks and pieces of cloth. Despite numerous attempts, with 15 different infants as subjects, she found no evidence of conditioning. One possibility, suggested by Martin Seligman (1971), is that people are biologically predisposed to acquire fears of situations and objects, such as rats and snakes, that posed a threat to our evolutionary ancestors and are less disposed to acquire fears of other situations and objects. More recently, Susan Mineka and her colleagues (1984) showed that rhesus monkeys are not afraid of snakes when first exposed to them but easily learn to fear them. In one experiment, monkeys raised in the laboratory did not react fearfully to snakes until they saw a monkey that had been raised in the wild do so. In subsequent experiments, Michael Cook and Mineka (1989, 1990) used splicing to produce films in which a monkey was shown reacting fearfully in the presence of various objects, including toy snakes, flowers, and a toy rabbit. Through observing the films, monkeys that previously feared none of these objects developed a fear of toy snakes (and real snakes) but not of flowers or toy rabbits. In some regions where rhesus monkeys live there are dangerous snakes, but in other regions all of the snakes are harmless. In places where snakes are harmless, an inflexible instinctive fear of them would be maladaptive. Thus, the learning mechanism may have evolved because it allows monkeys living in areas where snakes are dangerous to learn quickly to fear and avoid them, while it allows monkeys living elsewhere to go about their business relatively oblivious to snakes. The infants initially showed no greater fear to the snakes than to the other animals, suggesting that a fear of snakes is not inborn. The infants and toddlers then saw brief video clips of snakes and other animals associated with either a happy or fearful voice. Both the infants and toddlers looked longer at the snakes when they heard the fearful voice than when they heard the happy voice. There was no difference in looking time to the two voices when they saw videos of other animals. Precocial birds are those species-such as chickens, geese, and ducks-in which the young can walk almost as soon as they hatch. To avoid that, they have acquired, through natural selection, an efficient means to determine who their mother is and a drive to remain near her. The means by which they learn to recognize their mother was discovered by Douglas Spalding near the end of the nineteenth century. Spalding (1873/1954) observed that newly hatched chicks that were deprived of their mother, and that happened to see him (Spalding) walk by shortly after they were hatched, would follow him as if he were their mother. They continued to follow him for weeks thereafter, and once attached in this way they would not switch to following a real mother hen. Some 60 years later, Konrad Lorenz (1935/1970) made the same discovery with newly hatched goslings. Lorenz labeled the phenomenon imprinting, a term that emphasizes the very sudden and apparently irreversible nature of the learning process involved. One interesting feature of imprinting is the rather restricted critical period during which it can occur. Spalding (1873/1954) found that if chicks were prevented from seeing any moving object during the fi rst 5 days after hatching and then he walked past them, they did not follow. In more detailed studies, Eckhard Hess (1958, 1972) found that the optimal time for imprinting mallard ducklings is within the first 18 hours after hatching. Although early studies suggested that young birds could be imprinted on humans or other moving objects as easily as on their mothers, later studies proved otherwise. Given a choice between a female of their species and some other object, newly hatched birds invariably choose to follow the former. These geese, which were hatched by Lorenz in an incubator, followed him everywhere, as if he were their mother. Newly hatched chicks will follow a box with a chicken head attached to it as readily as they will a complete stuffed chicken and more readily than any object without a chicken head (Johnson & Horn, 1988). The experience of following the object brings the imprinting mechanism in to play, and this mechanism causes the chicks to be attracted thereafter to all the features of the moving object (Bateson, 2000). Under normal conditions, of course, the moving object is their mother, so imprinting leads them to distinguish their mother from any other hen. If you put precocial birds such as ducks in circular tub and play the maternal call of their species from a speaker on one side and the maternal call of another species from a speaker on the opposite side, they will invariable approach the speaker playing the call from their own species. However, when ducklings are removed from their mothers and hatched in an incubator, they still approach their maternal call, even though they had never heard it before. But they have heard the peeping of the other ducklings in the brood of eggs, and their own peeps, for that matter. These experiments, done by Gilbert Gottlieb (1991), show that even something that looks like a clear-cut instinct such as auditory imprinting still involves some experience. Natural selection has worked so that the brain, sensory organs (in this case, those associated with hearing), and experience are coordinated to produce a valuable adaptive behavior. But as we stressed in Chapter 3, behavior is always the product of genes and experience, and it sometimes takes a lot of effort to discover what those experiences are. In sum, we have here a learning process for which the timing (the critical period), the stimulus features (characteristics typical of a mother bird of the species), and the behavioral response (following) are all genetically prepared-in interaction with the environment-in ways that promote its specific adaptive function-staying near the mother. How do all examples of specialized learning mechanisms influence thought about the concept of intelligence Specialized Place-Learning Abilities Many animals have specialized abilities for learning and remembering specific locations that have biological significance to them. A quite different example of specialized place learning is the ability of Pacific salmon to return to their hatching grounds. Then, when they are ready to spawn, they use their sense of smell to find their way back to the same stream from which they had come (Hasler & Larsen, 1955; Navitt et al. So, in certain very specific ways, species of birds and fish appear to be "smarter" than chimpanzees or people. The more we understand about animal behavior, the more it becomes apparent that intelligence is a relative concept. The intelligence of animals comes not from a general ability to reason but from specialized learning abilities that have evolved over thousands of generations in the wild. Their ability to remember each hiding place is an example of a specialized learning ability. Choosing Food Objects of Fear Imprinting on Mother Place Memory Rats and people avoid foods that they have eaten some minutes or hours before becoming ill. Such food avoidance learning differs in significant ways from general classical conditioning. Rats, and possibly humans, can learn to prefer foods associated with health improvement or nutritional gain. Observation of what others eat influences food choice, differently in rats and people. Human infants and toddlers are more attentive to snakes when they hear a fearful voice than a happy voice. Ducklings and goslings follow the first moving object they see within a critical period, and continue to follow it. Certain characteristics of imprinting help to ensure that, under normal conditions, the young of these species will learn to identify and follow their own mothers. Ducklings will approach the maternal call of their species shortly after hatching, and auditory experience while still in the egg is critical for this adaptive behavior to develop. Reflections and Connections In reviewing this or any chapter, it is useful to think not just about the relationships among ideas within each major section, but also about the relationships among ideas across sections. One way to do that, for the present chapter, is to think about the three different perspectives on learning that are referred to at various places in the chapter: the behavioral, cognitive, and evolutionary perspectives. A perspective is a point of view, a framework, a set of ground rules and assumptions that scientists bring to the topic studied. The perspective helps determine the kinds of questions asked, the kinds of evidence regarded as important, the kinds of studies conducted, and the vocabulary used to describe the observations. Here are some thoughts about each of the perspectives referred to in this chapter: 1. To be scientifically useful, however, cognitive constructs must make testable predictions about observable behavior, and most cognitive research involves such tests. The evolutionary perspective this is the perspective that most clearly unites the two chapters on adaptation-the preceding one on evolution and the present one on learning. While behaviorism and cognitivism have roots in philosophy, which has traditionally tried to understand human behavior and the human mind in terms of general principles that have wide applicability (such as principles of mental associations and the law of effect), the evolutionary perspective grew out of biology, which recognizes the diversity of life processes. The view that learning mechanisms are products of natural selection implies that they should be specially designed to solve biologically significant problems pertaining to survival and reproduction. In this chapter, the evolutionary perspective manifested itself most clearly in research having to do with the value of conditioning in helping animals to predict biologically significant events (such as foods, dangers, and opportunities for sex); the role of play in motivating animals to practice life-sustaining skills; the special human adaptations for observational learning; and the specialized, domainspecific learning mechanisms (such as for food preferences, fear learning, imprinting on the mother, and place learning) that are unique to certain species. These assumptions led behaviorists to focus heavily on classical and operant conditioning. The environmental conditions that produce learning, in these cases, can be described in terms of relationships among stimuli in the environment or between responses and stimuli (including reinforcing stimuli), and learning can be quantified in terms of immediate changes in behavior (increased frequency of conditioned responses). The cognitive perspective Among the pioneers of this perspective were psychologists, such as Tolman, who began as behaviorists but found that approach too limiting. They argued that you can go only so far in understanding learning (or anything else in psychology) without talking about mental processes. Depending on concepts, a person or animal can perceive two stimuli as similar even if they Find Out More John Alcock (2013). Beautifully illustrated and easy to read, the book explores the evolutionary puzzles provided by developmental and neurophysiological mechanisms. Alcock is a brilliant biologist who has the ability to convey excitement about the science of animal behavior on every page. Skinner-who wanted to be a novelist before he went in to psychology-is always fun to read, and there is no better way to begin than with this collection of essays. The titles include "Human Behavior and Democracy," "Why I Am Not a Cognitive Psychologist," "The Free and Happy Student," "The Force of Coincidence," and "Freedom and Dignity Revisited. In this clearly written, well-argued work, Flora advocates the intelligent use of reinforcement in parenting, educational settings, correctional institutions, and health-improvement programs. Bouton is a leading researcher on classical conditioning, and this is a well-written textbook on basic principles of learning, dealing especially with classical and operant conditioning. This collection of essays, each by one or more specialists in the subject, shows how the traditions of laboratory research on learning and naturalistic studies of animals in the wild have merged and begun to provide rich detail about species-typical learning processes.

Selenocysteine contains the trace element selenium in place of the sulfur atom of cysteine (Box 15-2 mens health august 2012 generic rogaine 2 60 ml free shipping. Interestingly mens health garcinia cambogia cheap rogaine 2 60 ml visa, selenocysteine is not incorporated in to proteins by chemical modification after translation (as is true for certain other unusual amino acids man health picture buy rogaine 2 canada, such as hydroxyproline prostate 64 discount rogaine 2 master card, which is found in collagen) man health over 50 buy rogaine 2 60ml visa. Thus mens health 042013 chomikuj effective 60ml rogaine 2, selenocysteine can be thought of as a twenty-first amino acid that is incorporated in to proteins by a modification of the standard translation machinery of the cell. In prokaryotes, the transcription machinery and the translation machinery are located in the same compartment. Translation 521 in which the coupling of transcription and translation is exploited during the regulation of gene expression, as we shall see in Chapter 18. In contrast to the situation in prokaryotes, translation in eukaryotes is completely separate from transcription. These events occur in separate compartments of the cell: transcription occurs in the nucleus, whereas translation occurs in the cytoplasm. Perhaps because of the lack of coupling to transcription, eukaryotic translation proceeds at the more leisurely speed of two to four amino acids per second. The large subunit contains the peptidyl transferase center, which is responsible for the formation of peptide bonds. By convention, the large and small subunits are named according to the velocity of their sedimentation when subjected to a centrifugal force. The unit used to measure sedimentation velocity is the Svedberg (S; the larger the S value the faster the sedimentation velocity and the larger the molecule), which is named after the Nobel Laureate and inventor of the ultracentrifuge, Theodor Svedberg. In bacteria, the large subunit has a sedimentation velocity of 50 Svedberg units and is accordingly known as the 50S subunit, whereas the small subunit is called the 30S subunit. The explanation for this apparent discrepancy is that sedimentation velocity is determined by both shape and size and hence is not an exact measure of mass. The eukaryotic ribosome is somewhat larger, composed of 60S and 40S subunits, which together form an 80S ribosome. New Amino Acids Are Attached to the Carboxyl Terminus of the Growing Polypeptide Chain As we know, both polynucleotide and polypeptide chains have intrinsic polarities. Thus, for each of these molecules, we can ask which end of the chain is synthesized first. This was first determined in a classic experiment performed by Howard Dintzis that is described in Chapter 2. This experiment found that each new amino acid must be added to the carboxyl terminus of the growing polypeptide chain (often referred to as synthesis in the amino- to carboxy-terminal direction). As described in the next section, this directionality is a direct result of the chemistry of protein synthesis. This reaction occurs between the amino acid residue at the carboxy-terminal end of the growing polypeptide and the incoming amino acid to be added to the chain. First, this mechanism of peptide-bond formation requires that the amino terminus of the protein be synthesized before the carboxyl terminus. For this reason, the reaction to form a new peptide bond is called the peptidyl transferase reaction. Interestingly, peptide-bond formation takes place without the simultaneous hydrolysis of a nucleoside triphosphate. The schematic illustration of the ribosome shows the three binding sites (E, P, and A) that each spans the two subunits. The answer is provided by the structure of the ribosome, which reveals "tunnels" in and out of the ribosome. A second channel through the large subunit provides an exit path for the newly synthesized polypeptide chain. In this case, a polypeptide can form an a helix within the channel, but other secondary structures (such as b sheets) and tertiary interactions can form only after the polypeptide exits the large ribosomal subunit. For this reason, the final 3D structure of a newly synthesized protein is not attained until after it is released from the ribosome. In this image, the 50S subunit is cut in half to reveal the polypeptide exit tunnel. Our description will proceed in order through the three stages of translation: initiation of the synthesis of a new polypeptide chain, elongation of the growing polypeptide, and termination of polypeptide synthesis. As we shall see, there are important similarities and differences between prokaryotes and eukaryotes in the strategies they use to perform these events. We shall consider the nature of the translation machinery from both kinds of cells in each of the following sections. We start by addressing the initiation events in prokaryotes and then discuss the differences observed in eukaryotic cells. The large subunit joins its partner only at the very end of the initiation process, just before the formation of the first peptide bond. Thus, many of the key events of translation initiation occur in the absence of the full ribosome. This is not the case, however, because an enzyme known as a deformylase removes the formyl group from the amino terminus during or after the synthesis of the polypeptide chain. In fact, many mature prokaryotic proteins do not even start with a methionine; aminopeptidases often remove the amino-terminal methionine as well as one or two additional amino acids. As we have seen for other molecular processes (such as promoter recognition during transcription), eukaryotic cells require more auxiliary proteins to drive the initiation process than do prokaryotes. They recruit the small subunit to bind and initiate even in the absence of a 50 cap (Box 15-3. Although initiation in eukaryotic cells involves many more auxiliary factors, there are clear analogs of the bacterial initiation factors. There are three key events that must occur for the correct addition of each amino acid. Unlike the initiation of translation, the mechanism of elongation is highly conserved between prokaryotic and eukaryotic cells. We limit our discussion to translation elongation in prokaryotes, which is understood in the greatest detail, but the events that occur in eukaryotic cells are similar to those in prokaryotes, both in the factors involved and in their mechanism of action. That is, no more than one in every 1000 amino acids incorporated in to protein is incorrect. These bases form hydrogen bonds with the minor groove of each correct base pair formed between the anticodon and the first two bases of the codon in the A-site. In both cases, formation of correct base-pairing interactions dramatically enhances the rate of a critical biochemical step. Early evidence for this came from experiments in which it was shown that a large subunit that had been largely stripped of its proteins was still able to direct peptide bond formation. To test this possibility, the nine amino acids at the L27 amino terminus that were in close proximity to the active site were eliminated by mutation. The resulting cells produced ribosomes with reduced but detectable peptidyl transferase activity, clearly indicating that this region of the L27 protein contributes to peptidyl transferase activity. Clearly, the vast majority of this increase is retained, even without the presence of L27 in the active site. Thus, although this protein facilitates peptide-bond formation, it is not essential for peptide transferase activity. The exact mechanism remains to be determined, but some answers to this question are beginning to emerge. That is, the enzyme works by bringing the substrates together in a manner that stimulates catalysis. The red arrows show the proposed direction of electron movement during peptide-bond formation. Nevertheless, there is still much to be learned regarding how the ribosome catalyzes peptide-bond formation. These movements are coordinated within the ribosome and are collectively referred to as translocation. Completion of translocation is accompanied by a clockwise rotation of the small subunit back to its starting position. How many molecules of nucleoside triphosphate does it cost per round of peptide-bond formation (setting aside the energetics of amino acid biosynthesis and the energetics of initiation and termination) The breakage of this high-energy bond drives the peptidyl transferase reaction that creates the peptide bond. Throughout the discussion of translation elongation, we have not distinguished between prokaryotes and eukaryotes. Short Regions of Class I Release Factors Recognize Stop Codons and Trigger Release of the Peptidyl Chain How do release factors recognize stop codons For this reason, this three-amino-acid sequence is called a peptide anticodon and must interact with and recognize stop codons. In this structure, the peptide anticodon is located very near the anticodon, but it is likely that there are additional protein regions that contribute to codon recognition. Indeed, these bases appear to play a more important role in peptide release than they do in peptide-bond formation. Like initiation and elongation, the termination of translation is mediated by an ordered series of interdependent factor binding and release events. This ordered nature of translation ensures that no one step occurs before the previous step is complete. There is a weakness to this orderly approach to translation: if any step cannot be completed, then the entire process stops. One advantage of control of translation over transcription is the ability to respond very rapidly to external stimuli. As with other types of regulation, translational control typically functions at the level of initiation. It is generally more efficient to regulate a pathway at an earlier step rather than starting a process and then stopping it. In the case of translation, regulation at the level of initiation also eliminates the production of incomplete proteins that might have altered function. In this section, we first describe general mechanisms used by bacteria and eukaryotic cells to regulate translation. In many cases, this inhibition is modulated by the translation of other genes in the same operon. In many instances, disruption occurs as a consequence of translating another gene in the operon. Regulation of Prokaryotic Translation: Ribosomal Proteins Are Translational Repressors of Their Own Synthesis We now present an example of regulation of translation in bacteria that illustrates how the cell uses these mechanisms to control correct expression of ribosomal protein genes. The most widely used antibiotics in medicine kill bacteria but have little or no effect on eukaryotic cells and hence are not toxic to the patient. Since their discovery in the first half of the last century, antibiotics have helped make previously untreatable infections such as tuberculosis, bacterial pneumonia, syphilis, and gonorrhea largely curable (although the emergence of antibiotic-resistant bacteria is becoming an increasing obstacle to effective treatment). Antibiotics have many different kinds of targets in the bacterial cell, but 40% of the known antibiotics are inhibitors of the translation machinery (Box 15-5 Table 1). In general, these antibiotics bind a component of the translation apparatus and inhibit its function. Because different antibiotics arrest translation at different steps and do so in a precise manner. Thus, in addition to their obvious medical benefits, antibiotics have come to play an important role in helping us understand the workings of the translation machinery. Thus, peptidyl chains that are transferred to puromycin dissociate from the ribosome as an incomplete, puromycin-bound polypeptide. Other antibiotics target other features of the ribosome, such as the peptide exit tunnel, the peptidyl transferase center, the factorbinding center, the decoding center, and regions critical for translocation (Box 15-5 Table 1). In both cases, the next step in translation is prevented by the failure to release the elongation factor. Once completed, puromycin and any associated polypeptide diffuse out of the ribosome. Changes in growth conditions quickly lead to an appropriate increase or decrease in the rate of synthesis of all ribosomal components. Coordinate regulation of ribosomal protein genes is simplified by their organization in to several operons, each containing genes for up to 11 ribosomal proteins. It is easy to see how ribosomal protein binding prevents translation of the initial gene in the operon. The protein that acts as a translational repressor of the other proteins is shaded red. As we discussed above in the chapter, translational coupling may occur when the stop codon of an upstream gene is located very close to the start codon of a downstream gene. This proximity can create a situation in which translation of the upstream gene is required for translation of the downstream gene. If this binding site is unoccupied, then the ribosomal protein will preferentially bind there. This simple competitive binding event ensures that ribosomal protein synthesis is inhibited only when the regulatory ribosomal protein is in excess. Not surprisingly, in several instances, the two binding sites for the regulatory ribosomal protein are related to each another. In the case of the S8 ribosomal protein, the two binding sites share substantial similarities. In this example, we describe a simplified two-protein ribosomal protein gene operon. This strategy for translational inhibition is not restricted to ribosomal proteins. Recall from our earlier discussion of initiation of eukaryotic translation that these events occur independently of one another, but inhibition of either eliminates new protein synthesis. Growth factors, hormones, and other factors that stimulate cell division activate this kinase and therefore increase the overall translational capacity of the cell. These observations have led to the hypothesis that the control of translation capacity is carefully coordinated with cell proliferation.

The mouse prostate cancer 72 year old trusted 60 ml rogaine 2, however mens health 28 day muscle discount generic rogaine 2 canada, enjoys a special status because of its exalted position on the evolutionary tree: it is a mammal and androgen hormone used to detect purchase rogaine 2 in india, therefore androgen hormone for endometriosis purchase rogaine 2 60 ml without a prescription, related to humans prostate female order 60ml rogaine 2 overnight delivery. Of course man health buy now tramadol order rogaine 2 60ml otc, chimpanzees and other higher primates are closer to humans than mice, but they are not amenable to the various experimental manipulations available in mice. Thus, the mouse provides the link between the basic principles, discovered in simpler creatures like worms and flies, and human disease. For example, the patched gene of Drosophila encodes a critical component of the Hedgehog receptor (Chapter 21). Mutant fly embryos that lack the wild-type patched gene activity exhibit a variety of patterning defects. Unexpectedly, however, certain patched mutants cause various cancers, such as skin cancer, in both mice and humans. In addition, methods have been developed that permit the efficient removal of specific genes in otherwise normal mice. This "knockout" technology continues to have an enormous impact on our understanding of the basic mechanisms underlying human development, behavior, and disease. The chromosome complement of the mouse is similar to that seen in humans: there are 19 autosomomes in mice (22 in humans), as well as X 826 Appendix 1 fertilization maternal pronucleus sperm head expands paternal pronucleus 1st cleavage and Y sex chromosomes. There is extensive synteny between mice and humans: extended regions of a given mouse chromosome contain the same set of genes (in the same order) as the "homologous" regions of the corresponding human chromosomes. As discussed in Chapter 21, the mouse has virtually the same complement of genes as those present in the human genome: each contains approximately 25,000 genes, and there is a one-to-one correspondence for more than 85% of these genes. Most, if not all, of the differences between the mouse and human genomes stem from the selective duplication of certain gene families in one lineage or the other. Comparative genome analysis confirms what we have known for some time: the mouse is an excellent model for human development and disease. In addition, it is possible to harvest enough mouse embryos, even at the earliest stages, for in situ hybridization assays and the visualization of specific gene expression patterns. Such visualization methods can be applied to both normal embryos and mutants carrying disruptions in defined genetic loci. The first obvious diversification of cell types is seen at the 16-cell stage, called the morula. The cells located in outer regions form tissues that do not contribute to the embryo but instead develop in to the placenta. Interactions between the blastocyst and uterine wall lead to the formation of the placenta, a characteristic of all mammals except the primitive egg-laying platypus. Shortly thereafter, a fetus emerges that contains a brain, a spinal cord, and internal organs such as the heart and liver. A groove called the primitive streak forms along the length of the epiblast and the cells that migrate in to the groove form the internal mesoderm. Double mutant mouse embryos that lack both genes develop in to fetuses that lack head structures such as the forebrain and nose. The efficiency of integration is quite high and usually occurs during early stages of development, often in onecell embryos. Consider as an example a fusion gene containing the enhancer from the Hoxb2 gene attached to a lacZ reporter gene. Embryos and fetuses can be harvested from transgenic strains carrying this reporter and stained to reveal the pattern of lacZ expression. Transgenic mice have been used to characterize several regulatory sequences, including those that regulate the b-globin genes and HoxD genes. A strain of mice has been established that is completely normal except for the removal of the p53 gene. There is the hope that these mice can be used to test potential drugs and anticancer agents for use in humans. Although Drosophila contains a p53 gene, and mutants have been isolated, it does not provide the same opportunity for drug discovery as does the mouse model. A transgenic strain of mice was created that contains a portion of the Hoxb2 regulatory region attached to a lacZ reporter gene. Embryos were obtained from transgenic females and stained to reveal sites of b-galactosidase (LacZ) activity. Once produced, these cells can be cloned and used to generate a complete mouse lacking that same gene. The thymidine kinase gene is carried outside the region of homology with the chromosome in the vector. Hence, transformants in which the mutant gene has been incorporated in to the chromosome by homologous Model Organisms 829 recombination will shed the thymidine kinase gene, but transformants in which incorporation in to the chromosome occurred by illicit recombination will frequently contain the entire vector with the thymidine kinase gene and hence can be selected against. The hybrid embryos are inserted in to the oviduct of a host mouse and allowed to develop to term. Some of the adults that arise from the hybrid embryos possess a transformed germ line and therefore produce haploid gametes containing the mutant form of the target gene. Once mice are produced that contain transformed germ cells, matings among siblings are performed to obtain homozygous mutants. With other genes, the mutant embryos develop in to full-grown mice, which are then examined using a variety of techniques. Mice Exhibit Epigenetic Inheritance Studies on manipulated mouse embryos led to the discovery of a very peculiar mechanism of non-Mendelian, or epigenetic, inheritance. This is because the other copy is selectively inactivated either in the developing sperm cell or the developing egg. It encodes an insulin-like growth factor that is expressed in the gut and liver of developing fetuses. Only the Igf2 allele inherited from the father is actively expressed in the embryo. In other words, the paternal copy of the gene is "imprinted"-in this case, methylated-for future expression in the embryo. Many of the genes, including the preceding example of Igf2, control the growth of the developing fetus. It has been suggested that imprinting has evolved to protect the mother from her own fetus. The mother attempts to limit this growth by inactivating the maternal copy of the gene. The overall strategies for achieving these basic biological goals are similar in the vast majority of organisms and, therefore, may be examined rather successfully using simple organisms. It is, however, clear that the more intricate processes found in higher organisms, such as differentiation and development, require more complicated systems for regulating gene expression and that these can be studied only in more complex organisms. We have seen that a wide range of powerful experimental techniques can be used with success to manipulate the mouse and to explore various complex biological problems. As outlined in the text, and described in detail in Chapter 19, imprinting ensures that only one copy of the mouse Igf2 gene is expressed in each cell. The recent publication and annotation of the mouse genome has underscored the importance of the mouse as a model for further exploring and understanding problems in human development and disease. The F1 generation shows an intermediate phenotype when true-breeding red and white snapdragons cross. A gene may have more than one allele, and the relationship between each allele relative to another has to be determined. A low mutation rate allows organisms to adapt to changes in their environment over time. The value 15 must be the lowest value for observed recombinant progeny since a double crossover is the least likely event. From the information given, you know pk is in between y and tri, so 15 represents the total observed crossover between both y and pk and pk and tri. For the observed recombinants, you add the value for the double crossovers because the single crossover did occur in those progeny. Through polyribsomes, the translation of a specific protein is increased and the time to reach a certain level of that protein is decreased. The nitrogenous bases have a pyrimidine (cytosine and thymine) or purine (adenine and guanine) ring structure. Nucleotides include a nitrogenous base bound to a ribose or deoxyribose, which is bound to one, two, or three phosphate groups (mono-, di-, or triphosphate). So the resulting band after ultracentrifugation in a cesium chloride gradient would correspond to an intermediate band. So the resulting bands after ultracentrifugation in a cesium chloride gradient would correspond to one heavy band and one light band. The conservative model of replication can be eliminated in one round of bacterial replication, but two rounds of replication are required to distinguish between the dispersive and the semiconservative models. Polar molecules have a dipole moment, whereas nonpolar molecules do not have a dipole moment. The side chain of glutamate includes a carboxylic acid capable of participating in hydrogen bonds. A, hydrogen bond acceptor; D, hydrogen bond donor; H, nonpolar hydrogens; M, methyl groups. To determine if the genetic material is single-stranded or doublestranded, examine the percentages of each base. If the percentages do not show either pattern, then the genetic material is likely single-stranded. Uracil differs from thymine by the absence of a methyl group at the fifth carbon as in thymine. Because the substrate is not attached to the catalytic portion of the hammerhead, the substrate can be released to allow for a new molecule to bind. The hammerhead is now a true ribozyme, capable of completing many rounds of the reaction. An ionic bond can form between the side chain of an acidic amino acid (aspartic acid or glutamic acid) and a basic amino acid (lysine, arginine, or histidine). In peptide bond formation, the carboxyl group of one amino acid covalently bonds with the amino group of another amino acid through the elimination of water. Because two molecules form a bond with the loss of water, the reaction is called a condensation or dehydration reaction (specific to the loss of water). Monomeric myoglobin has no quaternary structure; tetrameric hemoglobin has quaternary structure that is critical for its physiological function. Both proteins are globular, and their folded subunits are largely a-helical; their secondary and tertiary structures are similar. Primary structure dictates secondary and tertiary structure; the primary structures of myoglobin and hemoglobin are therefore likely to be similar. A b strand is a single unit of secondary structure; a b sandwich is an example of protein tertiary structure (a particular kind of folded domain). The two histidines and two cysteines are critical for coordination of the Zn2, which is in turn a critical stabilizing element for the very small, Zn-finger domain. Substituting alanine for any one of these four residues will eliminate Zn2 binding and destabilize the domain, leading to loss of function. Enzymes appear to do so in many cases because their active sites are complementary to the transition-state conformations of the reactants, rather than to the ground-state conformations- that is, there are favorable noncovalent interactions between the enzyme and the transition-state forms of its substrates. The results agree with the complementation assay, but they suggest that, in vitro, three repeats are not sufficient for full activity. These discrepancies suggest some redundancy of function, either among the Tif3 domains or with other components of the translation initiation complex. For a restriction enzyme that recognizes a 6-bp sequence, the frequency of finding that sequence in a given genome is 1 in 46 or 1 in 4096 bp. Even though the recognition sequences differ for XhoI and SalI, the sticky ends can base-pair with each other because the single-stranded regions are complementary to each other. Affinity chromatography separates proteins based on interaction with a specific molecule, protein, or nucleic acid that is coupled to the beads. Digestion of a strand labeled at both ends would complicate the pattern and obscure the "footprint. To determine if a specific known region is bound to the protein, use primers that are specific to those sequences to amplify that sequence and compare the results to necessary controls. The northern blot indicates that 835 there are two transcripts for Gene Z in embryonic flies but only one transcript in adult flies. For the hypothesis given, you could use a new antibody against Protein Z in the western blot. This antibody could be polyclonal to the whole protein or be monoclonal against a central or amino-terminal region of the protein. If you see a second band on the western blot in the embryo lane when using the new antibody, the data would support the hypothesis proposed in part A. The nucleus, unlike the nucleoid, is membrane-bound and typically occupies a small fraction of the cell volume.

The presence of dideoxycytosine in the growing chain (shown at the bottom) blocks further addition of incoming nucleotides as described in the text prostate cancer levels 1-10 buy 60 ml rogaine 2 mastercard. The length of the fragments therefore specifies the position of Cs in the template strand prostate cancer tattoo discount rogaine 2 master card. To read that sequence prostate and bladder buy discount rogaine 2 60 ml on line, the fragments generated in each of the four reactions are resolved on a polyacrylamide gel mens health 3 month workout plan cheap rogaine 2 60ml with amex. As described in the text mens health urbanathlon san francisco purchase rogaine 2 now, chains of different length are synthesized in the presence of dideoxynucleotides prostate oncology websites discount rogaine 2 60 ml without prescription. In this reaction, all bases are present as deoxynucleotides, but G is present in the dideoxy form as well. Shotgun Sequencing a Bacterial Genome the bacterium Haemophilus influenzae was the first free-living organism to have a complete genome sequence and assembly. It was a logical choice because it has a small, compact genome that is composed of just 1. This method might seem tedious, but it is considerably faster and less expensive than the techniques that were originally envisioned. Consequently, additional rounds of digestion, mapping, and sequencing would be required to obtain a complete sequence for any given defined region of the genome. This process is conceptually similar to the assembly of a giant dense crossword puzzle in which the determined words give clues to the overlapping but unknown words. Automated sequencing machines-Sequenators-were developed that have 384 separate fractionation columns. In a 9-h day, each machine can produce three sequencing "runs" and more than one-half a megabase (500 kb) of sequence information. There are currently five major sequencing centers in the United States and the United Kingdom. In this reaction, as described in the text, fluorescently end-labeled dideoxynucleotides are used, and the chains are separated by column chromatography. The profile of positions of As is represented in green, Ts in red, Gs in black, and Cs in blue. This problem is rapidly becoming even more severe as the methods for sequencing are becoming increasingly faster and more powerful. We now consider how the shotgun-sequencing method used to determine the complete sequence of the H. The collection of small fragments, each derived from individual chromosomes, is then reduced in to pools. Typically, two or three pools are constructed for fragments of differing (increasing) sizes-for example, fragments of 1, 5, or 100 kb in length. These fragments are then randomly cloned in to bacterial plasmids as we described above to make libraries. As discussed above for the sequencing of the bacterial chromosome, by sampling about 10 times the amount of sequence in a chromosome, we can be confident that every portion of the chromosome will be captured. However, a cluster of 100 384-column automated sequencing machines can generate 10-fold coverage of a human chromosome in just a few weeks. Thus, the key technological insight that facilitated the sequencing of the human genome was the reliance on automated shotgun sequencing and the subsequent use of computers to assemble the different pieces. Contigs are extended by the use of end sequences derived from the larger fragments carried in the 5-kb and 100-kb insert clones as described in the text. Sequences or "reads" that contain identical sequences are assumed to overlap and are joined to form larger contigs. The sizes of these contigs depend on the amount of sequence obtained-the more sequence, the larger the contigs and the fewer gaps in the sequence. For example, the Drosophila genome contains an average of one gene every 10 kb, thus a typical contig has several linked genes. Unfortunately, more complex genomes often contain considerably lower gene densities (see Chapter 8). Because the human genome contains an average of one gene every 100 kb, a typical contig is often insufficient to capture an entire gene, let alone a series of linked genes. One method that is used to overcome this difficulty is called paired-end sequencing. The end result is the construction of two libraries, one with small inserts and a second with larger inserts. Individual runs will produce 600 bp of sequence information at each end of the random insert. A record is kept of what end sequences are derived from the same inserted fragment. One end might align with sequences contained within contig A, whereas the other end aligns with a different contig, contig B. The principle of how these are used to produce long-range sequence information is the same as that described for the 5-kb inserts. The $1000 Human Genome Is within Reach the sequencing of the first two human genomes (one from the National Institutes of Health and the other from a private company) cost more than $300 million. There is now a campaign to use nanotechnology to produce rapid and inexpensive genome sequencing. The goal is to make the technology sufficiently rapid, simple, and inexpensive to permit the sequencing of individual genomes for clinical diagnosis. The first generation of high-throughput, nanotechnology sequencing machines is now available. The 454 Life Sciences sequencing machine generates up to 400 Mb of sequence information in a 4-h "run. The small size of the wells ensures that each one captures no more than a single bead. Sequential rounds of sequencing are detected by the release of pyrophosphate and light. The incorporation of a deoxynucleotide depends on the presence of the complementary base in the template and results in the liberation of pyrophosphate. This release promotes an enzymatic reaction that produces pulses of light, which are detected by a microprocessor attached to a computer. The sequence information is not necessarily sufficient to produce a de novo genome assembly. Rather, the finished human genome sequence produced by the National Institutes of Health is used as a template for comparison. The next generation of sequencing machines is approaching the goal of the $1000 genome. Illumina has produced a machine that can generate hundreds of millions of sequencing reads of 200 bp per run. The basic principle is similar to that seen for the 454 Life Sciences sequencing machine. In fact, as of this writing, nearly 200 different genomes have been sequenced and assembled. It is therefore possible to compare the complete genetic composition of many different microbes, plants, and animals. The unfilled portions of the 50 (left) and 30 (right) exons indicate non-coding sequences that do not contribute to the final protein product. FlyBase is the standardized database that is used to analyze the Drosophila genome. Bioinformatics Tools Facilitate the Genome-Wide Identification of Protein-Coding Genes Genome sequence assemblies correspond to contiguous blocks of millions of sequential As, Gs, Cs, and Ts encompassing every chromosome of the organism in question. Only when this information is available is it possible to catalog the complete coding capacity of the genome and compare its contents with those of other genomes. In this case, a variety of bioinformatics tools are required to identify genes and determine the genetic composition of complex genomes. Computer programs have been developed that identify potential proteincoding genes through a variety of sequence criteria. Nonetheless, computational methods have not yet been refined to the point of complete accuracy. Something like threefourths of all genes can be identified in this way, but many are missed, and even among the predicted genes that are identified, small exons-particularly non-coding exons-are often overlooked. Whole-Genome Tiling Arrays Are Used to Visualize the Transcriptome Once a whole-genome sequence is assembled for an organism, it can be used to comprehensively reveal all protein-coding and non-coding. The image represents a portion of a tiling array that has been hybridized with fluorescently labeled probes. Strong hybridization signals coincide with the exons, whereas there are weaker signals in the intronic regions. Based on the similar signals in all three colors this gene is expressed at similar levels at all three ages of embryos tested. The technology for genomewide tiling is advancing rapidly, and it is now feasible to produce complete arrays on a single glass slide or silicon chip that is just 1 cm2 in size. These probes might be derived from a specific cell type, such as the tail muscles of the sea squirt tadpole or yeast cells grown in a particular medium. The end result is a series of hybridization signals superimposed on all of the predicted proteincoding sequences across the genome. After labeling and hybridization to the tiling array chip, exonic sequences display more intense signals than introns. Tiling arrays have led to a rather startling observation: about one-third of a typical genome is transcribed, even though just a fraction of this transcription corresponds to protein-coding sequences (just 5% in the case of the human genome). Many genes have remote, 50 -non-coding exons that reside far (sometimes a megabase or more) from the main body of the coding sequence. Once identified, a host of bioinformatics methods permits the determination of potential protein structure and function, for example, whether the protein contains any known domains or motifs or shares other features with known proteins. In fact, some refer to the regulatory sequences as the "dark matter" of the genome. However, it is likely that both animals, particularly mice, have at least 100,000 enhancers. Thus, these simple sequence alignments fail to capture the vast majority of regulatory sequences. The dashed rectangle identifies enhancers that mediate expression in the nervous system. The gene is expressed in several different tissues, but it shows particularly strong expression in heart precursor cells called cardiomyocytes. Experimental studies confirmed that this cluster of binding sites, located in the 50 -flanking region of the gene, function as a bona fide enhancer. Genome Editing Is Used to Precisely Alter Complex Genomes the preceding methods, genome assemblies and annotation, are descriptive. They provide detailed atlases of whole-genome maps but do not provide the type of functional information that molecular biologists crave. During the break repair event, desired changes are introduced specifically to modify the genomic sequence. The targeted cleavage is performed by specially tailored nucleases, typically zinc-finger nucleases and "meganucleases," engineered to cleave at a designated target site in the genome. An 140-bp sequence in the 50 -flanking region of the a-catenin gene is conserved in the mouse, rat, and human genomes. The mouse sequence has been shown to function as an authentic heartspecific enhancer. Although in some instances, the function of a protein can be studied in a complex mixture, these studies can often lead to ambiguities. For this reason, the purification of proteins is a major part of understanding their function. The purification of a protein is designed to exploit its unique characteristics, including size, charge, shape, and, in many instances, function. Purification of a Protein Requires a Specific Assay To purify a protein requires an assay that is unique to that protein. As we shall see in the discussion of immunoblotting, an antibody can be used to detect specific proteins in the same way. In many instances, it is more convenient to use a more direct measure for the function of the protein. Preparation of Cell Extracts Containing Active Proteins the starting material for almost all protein purifications are extracts derived from cells.

Cheap rogaine 2 online amex. Back Workout W/ Friends - Mens Health Magazine Cover.