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Clinical Director, UT Health San Antonio Joe R. and Teresa Lozano Long School of Medicine

However, prolonged exposure to severe trauma such as experienced by victims of prolonged physical or sexual abuse and survivors of the Holocaust may cause permanent psychological scars. Sleep problems can be lessened by brief treatment with an anti-anxiety drug such as a benzodiazepine like alprazolam (Xanax). However, long-tem use of these drugs can lead to disturbing side effects, such as increased anger. Potassium is thought to be therapeutically useful in many ways, including assisting in the treatment of alcoholism, acne, alleviating allergies, promoting the healing of burns, and preventing high blood pressure. It can also help with such problems as congestive heart failure, chronic fatigue syndrome, or kidney stones. People suffering from any of the above should consider increasing their intake of potassium after talking to a professional. Symptoms of potassium deficiency A deficiency of potassium in the blood is referred to as hypokalemia and manifests itself in many ways. Among the most serious are arthritis, high blood pressure, heart disease, stroke, cancer, and even infertility, as potassium constitutes a vital element of seminal fluid. Potassium deficiency will increase acid levels in the body, lowering the natural pH, which will have far reaching effects. If potassium levels are down, the liver cannot operate normally, particularly regarding transformation of glucose to glycogen. Potassium deficiency can cause problems with the formation of connective tissue, and can render normally strong body tissue vulnerable to all kinds of problems. The collagen of a healthy person is approximately as strong as steel, and the strength of bone tissue can be likened to that of cast iron. Lack of potassium may create a susceptibility to fractures, skin lesions that do not heal, or other connective tissue problems. So important is potassium for the protection of collagen that many natural health gurus claim that along with other vital nutrients, it constitutes an essential element of protection against premature aging. As long ago as the 1920s, Max Gerson was the first person ever to cure lupus lesions with a diet designed to reduce abnormally high sodium levels and raise potassium levels to normal, which was entirely raw fruit and vegetables. Potassium is essential to the efficient processing of foods in the body; without it they cannot be broken down into the proper compounds. This can lead to rheumatism, and is one reason why adequate potassium prevents rheumatism. Potassium requirements In the past potassium was more plentiful in the diet than salt, but gradually, the situation has been reversed. Mary McNulty Potassium Description Potassium is one of the electrolytes essential to the smooth running of the human body; in fact just about all bodily functions depend on it to some extent. It is also one of the most abundant minerals in the body, constituting 70% of the positive ions inside cells; the rest are a mixture of sodium, magnesium, calcium, arginine, and others. Potassium is distributed to the cells by a process of passive diffusion and is regulated by an enzyme called adenosinetriphosphatase together with the level of sodium concentration inside the cell. Potassium and sodium are antagonistic, which means that an imbalance of one will automatically cause an imbalance of the other; normally potassium should predominate inside the cell. General use Potassium is necessary for normal cell respiration; a deficiency can cause decreased levels of oxygen, which will reduce the efficiency of cell function. Adequate supplies of potassium are also required to regulate heartbeat, facilitate normal muscle contraction, regulate the transfer of nutrients to cells, and regulate kidney function and stomach juice secretion, among other things. Cooking and processing destroy potassium, and added salt further robs the body of vital potassium. This departure from traditional cooking of fresh homegrown fruit and vegetables is likely the cause of many health problems faced by modern society. Those who may need to take potassium supplements include women who take oral contraceptives, abusers of alcohol or drugs, smokers, athletes, workers whose job involves physical exertion, patients who have had their gastrointestinal tract surgically removed, anyone suffering from any degree of malabsorption syndrome, and vegetarians. People who have eating disorders, especially bulimia and anorexia, are particularly at risk from damage due to low potassium levels. Also, individuals who have been ill, anyone who has undergone surgery and those who are taking cortisone or digitalis preparations, and those suffering from high levels of stress will probably also have low potassium levels. However, in general, nutritionists recommend reducing salt intake and ensuring adequate supply by increasing the amount of fresh fruit and vegetables in the diet.

In fruit flies, for example, white is an X-linked recessive mutation that produces white eyes instead of the red eyes found in wild-type flies; apricot is an X-linked recessive mutation that produces light-orange-colored eyes. To carry out a complementation test on recessive mutations, parents that are homozygous for different mutations are crossed, producing offspring that are heterozygous. If the mutations are allelic (occur at the same locus), then the heterozygous offspring have only mutant alleles (a b) and exhibit a mutant phenotype: a a b b Complementation has occurred if an individual organism possessing two recessive mutations has a wild-type phenotype, indicating that the mutations are nonallelic genes. A lack of complementation occurs when two recessive mutations occur at the same locus, producing a mutant phenotype. When the complementation test is applied to white and apricot mutations, all of the heterozygous offspring have light-colored eyes, demonstrating that white eyes and apricot eyes are produced by mutations that occur at the same locus and are allelic. What types of crosses would you carry out to determine whether the brindle genes in bulldogs and in Chihuahuas are at the same locus The Complex Genetics of Coat Color in Dogs the genetics of coat color in dogs is an excellent example of how complex interactions between genes may take part in the determination of a phenotype. For thousands of years, people have been breeding dogs for particular traits, producing the large number of types that we see today. Each breed of dog carries a selection of genes from the ancestral dog gene pool; these genes define the features of a particular breed. The genome of the domestic dog was completely sequenced in 2004, greatly facilitating the study of canine genetics. The genetics of coat color in dogs is quite complex; many genes participate, and there are numerous interactions between genes at different loci. We will consider four loci (in the list that follows) that are important in producing many of the noticeable differences in color and pattern among breeds of dogs. In interpreting the genetic basis of differences in the coat color of dogs, consider how the expression of a particular gene is modified by the effects of other genes. Keep in mind that additional loci not listed here can modify the colors produced by these four loci and that not all geneticists agree on the genetics of color variation in some breeds. Hairs encoded by this allele have a "salt and pepper" appearance, produced by a band of yellow pigment on a black hair. Saddle markings (dark color on the back, with extensive tan markings on the head and legs). Bicolor (dark color over most of the body, with tan markings on the feet and eyebrows). Areas where the A locus is not expressed may appear as yellow, red, or tan, depending on the presence of particular genes at other loci. When As is present at the A locus, the four alleles at the E locus have the following effects: Em E ebr e Black mask with a tan coat. Brindle, in which black and yellow are in layers to give a tiger-striped appearance. Black pigment cannot be produced; pigmented dogs can be chocolate, liver, tan, or red. Allele S is completely dominant over alleles si, sp, and sw; alleles si and sp are dominant over allele sw (S > si, sp > sw). The relation between si and sp is poorly defined; indeed, they may not be separate alleles. Four alleles at this locus determine where the genotype at the A locus is expressed. The As allele allows dark pigment to be expressed; whether a dog is black depends on which genes are present at the B and E loci. As discussed earlier in the chapter, all black Labradors must carry at least one B allele and one E allele (B E ). Labrador retrievers are homozygous for the S allele, which produces a solid color; the few white spots that appear in some dogs of this breed are due to other modifying genes. X-linked traits, for example, are passed from father to daughter but never from father to son, and Y-linked traits are passed from father to all sons. Now, we will examine additional influences of sex, including the effect of the sex of an individual organism on the expression of genes on autosomal chromosomes, on characteristics determined by genes located in the cytoplasm, and on characteristics for which the genotype of only the maternal parent determines the phenotype of the offspring. Finally, we will look at situations in which the expression of genes on autosomal chromosomes is affected by the sex of the parent from whom the genes are inherited.

Because nucleic acids are unable to copy themselves, how could they be generated without proteins Transcription is, in fact, a highly selective process: individual genes are transcribed only as their products are needed. But this selectivity imposes a fundamental problem on the cell-the problem of how to recognize individual genes and transcribe them at the proper time and place. They saw within the cell Christmas-tree-like structures: thin central fibers (the trunk of the tree), to which were attached strings (the branches) with granules (Figure 13. Their conclusion was that each "Christmas tree" represented a gene undergoing transcription. In most organisms, each gene is transcribed from a single strand, but different genes may be transcribed from different strands, as shown in Figure 13. How does the complex of enzymes and proteins that performs transcription-the transcription apparatus-recognize a transcription unit In most transcription units, the promoter is located next to the transcription start site but is not, itself, transcribed. The third component of the transcription unit is the terminator, a sequence of nucleotides that signals where transcription is to end. By convention, the sequence on the nontemplate strand is written with the 5 end on the left and the 3 end on the right. The first nucleotide transcribed (the transcription start site) is numbered +1; nucleotides downstream of the start site are assigned positive numbers, and nucleotides upstream of the start site are assigned negative numbers. So, nucleotide +34 would be 34 nucleotides downstream of the start site, whereas nucleotide -75 would be 75 nucleotides upstream of the start site. Each accessory protein is responsible for providing or regulating a special function. These antibiotics are widely used to treat tuberculosis, a disease that kills almost 2 million people worldwide each year. All eukaryotic polymerases are large, multimeric enzymes, typically consisting of more than a dozen subunits. The subunit is not essential for transcription, but it helps stabilize the enzyme. Other functional subunits join and leave the core enzyme at particular stages of the transcription process. As in bacterial cells, a number of accessory proteins bind to the core enzyme and affect its function. The consensus sequence comprises the most commonly encountered nucleotides at each site. We will first examine each of these steps in bacterial cells, where the process is best understood; then we will consider eukaryotic and archaeal transcription. Furthermore, the spacing and location of these nucleotides relative to the transcription start site are similar in most promoters. These short stretches of common nucleotides are called consensus sequences; "consensus sequence" refers to sequences that possess considerable similarity, or consensus (Figure 13. The presence of consensus in a set of nucleotides usually implies that the sequence is associated with an important function. Transcription initiation requires that the transcription apparatus recognize and bind to the promoter. Different genes are transcribed with different frequencies, and promoter binding is primarily responsible for determining the frequency of transcription for a particular gene. The function of these consensus sequences in bacterial promoters has been studied by inducing mutations at various positions within the consensus sequences and observing the effect of the changes on transcription. The results of these studies reveal that most base substitutions within the -10 and -35 consensus sequences reduce the rate of transcription; these substitutions are termed down mutations because they slow down the rate of transcription. Occasionally, a particular change in a consensus sequence increases the rate of transcription; such a change is called an up mutation. As mentioned earlier, the sigma factor associates with the core enzyme (Figure 13. Although it binds only the nucleotides of consensus sequences, the enzyme extends from -50 to +20 when bound to the promoter.

The course may be fulminant, with bacterial seeding of many organs, particularly vascular sites. Avoidance of antimotility agents, which may prolong symptoms and are associated with toxic megacolon 3. Antibiotic treatment does not benefit all pts but is indicated in cases with high fever, bloody and/or severe diarrhea, disease persistence for >1 week, or worsening symptoms. Shigellae survive the low pH of the gastric acid barrier, and as few as 100 organisms can cause infection. Shigella causes extensive ulceration of the epithelial surface of the colonic mucosa. Pts can remain asymptomatic, develop fever with or without watery diarrhea, or experience a progression to bloody diarrhea and dysentery characterized by small volumes of bloody, mucopurulent stools with associated severe abdominal cramping and tenesmus. Severe cases occur most often in children <5 years of age; disease may progress to toxic dilatation, colonic perforation, rectal prolapse, and death. The syndrome is defined by a triad of microangiopathic, Coombs-negative hemolytic anemia; thrombocytopenia; and acute renal failure due to glomerular capillary thromboses. In the United States, because of the ready transmissibility of Shigella, antibiotics are recommended. Rehydration usually is not needed; Shigella infection rarely causes significant dehydration. Septicemia and metastatic focal infections can occur in pts with chronic liver disease, malignancy, diabetes mellitus, and other underlying illnesses. Diagnosis Stool culture studies for Yersinia must be specifically requested and require the use of special media. Yersiniosis Antibiotics are not indicated for diarrhea caused by yersiniae; supportive measures suffice. The incidence is high in developing countries and among travelers, recent immigrants, men who have sex with men, and inmates of institutions in developed nations. Infection follows ingestion of cysts from fecally contaminated water, food, or hands. Amebomas-inflammatory mass lesions-may develop in chronic amebic intestinal disease. Most pts are febrile and have right upper quadrant pain that can radiate to the shoulder, point tenderness over the liver, and right-sided pleural effusion. At least three fresh stool specimens should be examined for amebic cysts or trophozoites. Sigmoidoscopy with biopsy of ulcers (often flask-shaped) may aid in the diagnosis but poses a risk of perforation. Serologic assays (enzyme-linked immunosorbent assay and agar gel diffusion) are positive in >90% of pts with colitis, amebomas, or liver abscess. The cell culture cytotoxin test is specific but less sensitive and also takes 48 h.