By W. Riordian. Xavier University of Louisiana.
The androgen pathway is unaffected buy zyvox 600mg otc antibiotics zoloft interaction, and the increased ACTH levels may Estrogens Testosterone increase the levels of adrenal androgens in the blood purchase zyvox 600mg free shipping infection under toenail. A third possible enzyme deficiency is that of 17- hydroxylase. A defect in 17- hydroxylase leads to aldosterone excess and Fig. These weak hypertension; however, because adrenal androgen synthesis requires this enzyme, no viril- androgens are converted to testosterone or ization occurs in these patients. In its target cells, the double bond in ring A of testosterone ing androgen is testosterone. Approx- is reduced through the action of 5- reductase, forming the active hormone dihy- imately 50% of the testosterone in the drotestosterone (DHT). Synthesis of Estrogens and Progesterone remaining half is derived from ovarian and adrenal androstenedione, which, after secretion Ovarian production of estrogens, progestins (compounds related to progesterone), into the blood, is converted to testosterone in and androgens requires the activity of the cytochrome P450 family of oxidative adipose tissue, muscle, liver, and skin. The adre- enzymes used for the synthesis of other steroid hormones. Ovarian estrogens are nal cortex, however, is the major source of the C18 steroids with a phenolic hydroxyl group at C3 and either a hydroxyl group relatively weak androgen dehydroepiandros- (estradiol) or a ketone group (estrone) at C17. The serum concentration of its ing compartments of the ovary (the granulosa cell, the theca cell, the stromal cell, stable metabolite, DHEAS, is used as a measure of adrenal androgen production in hyperandro- and the cells of the corpus luteum) have all of the enzyme systems required for the genic patients with diffuse excessive growth of synthesis of multiple steroids, the granulosa cells secrete primarily estrogens, the secondary sexual hair, e. The ovarian granulosa cell, in response to stimulation by follicle-stimulating hormone (FSH) from the anterior pituitary gland and through the catalytic activity of P450 aromatase, converts testosterone to estradiol, the predominant and most potent of the ovarian estrogens (see Fig. Similarly, androstenedione is con- The results of the blood tests on verted to estrone in the ovary, although the major site of estrone production from Vera Leizd showed that her level of androstenedione occurs in extraovarian tissues, principally skeletal muscle and adi- testosterone was normal but that her pose tissue. Which tissue was the most likely source of the androgens that caused Vera’s hirsutism (a male XI. VITAMIN D SYNTHESIS pattern of secondary sexual hair growth)? Vitamin D is unique in that it can be either obtained from the diet (as vitamin D2 or D3) or synthesized from a cholesterol precursor, a process that requires reactions in the skin, liver, and intestine. The calciferols, including several forms of vitamin D, Ergosterol is the provitamin of vita- are a family of steroids that affect calcium homeostasis (Fig. Cholecalciferol min D , which differs from 7-dehy- (vitamin D3) requires ultraviolet light for its production from 7-dehydrocholesterol 2 drocholesterol and vitamin D3, present in cutaneous tissues (skin) in animals and from ergosterol in plants. This irra- respectively, only by having a double bond diation cleaves the carbon–carbon bond at C9–C10 to open the B ring to form chole- between C22 and C23 and a methyl group at calciferol, an inactive precursor of 1,25-(OH)2-cholecalciferol (calcitriol). Vitamin D2 is the constituent in many is the most potent biologically active form of vitamin D (see Fig. The antirachitic potencies the kidney, where the pathway is regulated. In this activation process, carbon 25 of of D2 and D3 in humans are equal, but both vitamin D2 or D3 is hydroxylated in the microsomes of the liver to form 25-hydrox- must be converted to 25-(OH)-cholecalciferol ycholecalciferol (calcidiol). Calcidiol circulates to the kidney bound to vitamin and eventually to the active form calcitriol D–binding globulin (transcalciferin). In the proximal convoluted tubule of the kid- (1,25-(OH)2D3) for biologic activity. This step is tightly reg- Rickets is a disorder of young chil- ulated and is the rate-limiting step in the production of the active hormone. Low levels of calcium and (OH)D3 in its actions, yet 25-(OH)D3 is present in the blood in a concentration that phosphorus in the blood are associated with may be 100 times greater, which suggests that it may play some role in calcium and skeletal deformities in these patients. The biologically active forms of vitamin D are sterol hormones and, like other steroids, diffuse passively through the plasma membrane. In the intestine, bone, and kidney, the sterol then moves into the nucleus and binds to specific vitamin D3 receptors. This complex activates genes that encode proteins mediating the action of active vitamin D3. In the intestinal mucosal cell, for example, transcription of genes encoding calcium-transporting proteins is activated. These proteins are capa- ble of carrying Ca2 (and phosphorus) absorbed from the gut lumen across the cell, making it available for eventual passage into the circulation. CHAPTER 34 / CHOLESTEROL ABSORPTION, SYNTHESIS, METABOLISM, AND FATE 649 CH3 CH CLINICAL COMMENTS 3 H 2 CH2 CH2 CH H3C CH Ann Jeina is typical of patients with essentially normal serum triacyl- 3 H3C glycerol levels and elevated serum total cholesterol levels that are repeat- edly in the upper 1% of the general population (e. When similar lipid abnormalities are present in other family members in a pattern HO of autosomal dominant inheritance and no secondary causes for these lipid alter- 7–Dehydrocholesterol ations (e.
If DNA repair enzymes eration transcription factor 600mg zyvox mastercard antibiotic resistance efflux pump, related to c-myc) is amplified in some neu- are absent cheap 600 mg zyvox free shipping virus 2014 usa, mutations accumulate much more rapidly, and once a mutation develops roblastomas, and amplification of the erb-B2 in a growth regulatory gene, a cancer may arise. As an example, inherited mutations oncogene (a growth factor receptor) is asso- in the tumor suppressor genes brca1 and brca2 predispose women to the develop- ciated with several breast carcinomas. CHAPTER 18 / THE MOLECULER BIOLOGY OF CANCER 321 Proto-oncogene Promoter Coding region Normal DNA A. Gene amplification Mutation in Mutation in coding region promoter causes Expression of multiple copies causes production excessive expression of the proto-oncogene of hyperactive protein Strong promoter Gene Gene or enhancer X B. Y Gene rearrangement Proto-oncogene Proto-oncogene or is now under a portion of it is control of strong fused with another promoter or enhancer gene Fusion protein is either overproduced or hyperactive Fig. The mutations may be point mutations, deletions, or insertions. The proto-oncogene and the resulting oncogene are shown in blue. The protein products of these genes play roles in DNA repair, recombination, Although mutations in both the and regulation of transcription. A second example, HNPCC (hereditary non-poly- brca1 and brca2 genes are linked to posis colorectal cancer), was previously introduced in Chapter 13. It results from breast cancer development in women, there are some fundamental differ- inherited mutations in enzymes involved in the DNA mismatch repair system. ONCOGENES there are some differences in the diseases expressed by mutations within these genes. Proto-oncogenes control normal cell growth and division. These genes encode For example, brca1 mutations are also linked proteins that are growth factors, growth factor receptors, signal transduction pro- to ovarian cancer and brca2 mutations are teins, transcription factors, cell cycle regulators, and regulators of apoptosis not. Men with inherited brca2 muta- capitalized and italics are not used [e. The mutations in oncogenes tions develop breast cancer; but men who carry brca1 mutations do not. Oncogenes and Signal Transduction Cascades erbB-2) is over-expressed in 10 to 20% of breast cancer cases. When this gene is All of the proteins in growth factor signal transduction cascades are proto-onco- over-expressed, the prognosis for recovery is genes (Fig18. GROWTH FACTORS AND GROWTH FACTOR RECEPTORS and a resistance to therapy. Clinical trials are underway using a monoclonal antibody The genes for both growth factors and growth factor receptors are oncogenes. Preliminary results are encour- lular receptors located on the plasma membrane (cell-surface receptors) (see Chap- aging in that use of this drug, either alone or ter 11). Binding of ligands to these receptors stimulates a signal transduction path- in combination with others, appears to control way in the cell activating the transcription of certain genes. If too much of a growth the growth of some tumors overexpressing factor or a growth factor receptor is produced, the target cells may respond by pro- the HER2 gene. However, not all tumors over- liferating inappropriately. Growth factors receptors may also become oncogenic expressing HER2 are responsive to herceptin. Thus, it appears that a complete genotyping through translocation or point mutations in domains affecting binding of the growth of breast cancer cells may be necessary (using factor, dimerization, kinase activity, or some other aspect of their signal transmis- the microarray techniques described in Chap- sion. In such cases, the receptor transmits a proliferative signal even though the ter 17) to specifically develop an effective ther- growth factor normally required to activate the receptor is absent. In other words, apy for each patient with the disease. CHAPTER 18 / THE MOLECULER BIOLOGY OF CANCER 323 (I) Growth factor (II) Kinase (IV) G protein domain (III) Signal transduction proteins (V) Nonreceptor Activated protein kinases protein kinases (VI) Transcription factor Gene regulatory sequence Fig. Proto-oncogene sites for transforming mutations in growth factor signaling path- ways.
The energy in the aminoacyl- Enzyme-[aminoacyl–AMP] tRNA ester bond is subsequently used in the formation of a peptide bond during the tRNA process of protein synthesis zyvox 600 mg amex antibiotic cream for dogs. Some aminoacyl-tRNA synthetases use the anticodon of the tRNA as a recog- nition site as they attach the amino acid to the hydroxyl group at the 3 -end of AMP the tRNA (Fig buy zyvox 600mg infection vaginal. However, other synthetases do not use the anticodon but Enzyme recognize only bases located at other positions in the tRNA. PROCESS OF TRANSLATION O – P Translation of a protein involves three steps: initiation, elongation, and termination. It begins with the formation of the initiation complex. The amino acid is first activated by reacting with ATP. The amino acid is then transferred from the aminoacyl-AMP to tRNA. Some aminoacyl-tRNA synthetase recognition sites on tRNA. Each aminoacyl- tRNA synthetase is specific for one tRNA, which it “recognizes” by binding the sequences of nucleotides called the recognition sites, shown in blue. In some cases, the anticodon is a recognition site; in others, it is not. This is true for human tRNAs as well as those shown here. Once a tRNA has donated its amino acid to the growing polypeptide chain, it is released from the mRNA. A new aminoacyl-tRNA binds to the correct codon in the mRNA to donate its amino acid to the growing polypeptide chain. Termination occurs where the mRNA contains an in-frame stop codon, and the completed polypeptide chain is released. Initiation of Translation Eukaryotic initiation factor 2 (eIF2) In eukaryotes, initiation of translation involves formation of a complex composed and also elongation factor 1 (EF1) Met Met of methionyl-tRNAi , mRNA, and a ribosome (Fig. Methionyl-tRNAi are types of heterotrimeric G pro- Met (also known as Met-tRNAi ) initially forms a complex with the protein eukaryotic teins (see Chapter 11). They dramatically initiation factor 2 (eIF2), which binds GTP. This complex then binds to the small change their conformation and actively form (40S) ribosomal subunit. The cap at the 5 -end of the mRNA binds an initiation fac- complexes when they bind GTP but become tor known as the cap binding protein (CBP). CBP contains a number of subunits, inactive and dissociate when they hydrolyze this GTP to GDP. Several other eIFs join, and the mRNA then binds to the eIFs-Met- Met bound GDP to reactivate the initiation factor tRNAi – 40S ribosome complex. In a reaction requiring hydrolysis of ATP (due eIF2 or the elongation factor EF1. P site peptidyl site on the ribosome; A site aminoacyl site on the ribosome (The A and P sites or portions of them are indicated by dashed lines); eIF eukaryotic initiation factor. CHAPTER 15 / TRANSLATION: SYNTHESIS OF PROTEINS 265 Table 15. Differences between Eukaryotes and Prokaryotes in the Initia- Insulin, an anabolic hormone, stim- tion of Protein Synthesis ulates general protein synthesis by Eukaryotes Prokaryotes activating the initiation factor Binding of mRNA Cap at 5’ end of mRNA binds eIFs and Shine-Dalgarno sequence eIF4E. Normally, eIF4E is bound to an to small ribosomal 40S ribosomal subunit containing upstream of initiating AUG inhibitor protein, 4E binding protein (4E-BP). Ribosomes 80S 70S Phosphorylated 4E-BP no longer binds to (40S and 60S subunits) (30S and 50S subunits) eIF4E, and eIF4E is now free to participate in the initiation of protein synthesis. GTP is hydrolyzed, the initiation factors are released, and the large ribo- eIF2 is a regulator of the initiation somal (60S) subunit binds. It contains one small and step in protein synthesis.
Cartilage should be removed utilizing an oscillating saw and resect- ing only the distal half of the articular surface of the first metatarsal purchase 600 mg zyvox free shipping antibiotics gastritis. This cartilage should be transected in a plane that will be vertical with the foot buy 600mg zyvox with amex bacterial meningitis, usually with a 15° to 20° dorsal angulation to the longitudinal axis of the metatarsal. This distal phalanx then has its cartilage and surface resected par- allel to the distal phalanx. The two flat surfaces now will meet with the toe being in approximately 15° to 20° of dorsiflexion rel- ative to the longitudinal axis of the metatarsal. Additional dorsi- flexion at the first metatarsal phalangeal joint is indicated if there is any weight bearing on the proximal phalanx with the foot in neutral position. If this is a fully adult-sized patient, the ideal fixation is performed by using a 6. This screw provides excellent fixation but only works in an adult- sized foot (Figure S5. The hole for this screw is drilled retro- grade from the middle of the distal end of the metatarsal. The hole in the metatarsal is also tapped retrograde. A hole in the middle of the phalanx is opened with the drill, but tapping in not usually required. The other option for fixation is to use crossed K-wires or to use a four-hole plate on the dorsum of the metatarsal phalangeal joint. After the cast is re- moved, full activity is allowed as tolerated. Correction of Clawed Toes Indication Correction of claw toes in children with CP is only required if the toes are having nail problems from chronic pressure or are painful in shoes. If contracted flexor tendons are present with the clawed toes demon- strating flexion of the metatarsal phalangeal joint and interphalangeal joints, a direct plantar tenotomy with a number 11 knife is used, and the flexor tendons are cut just distal to the metatarsal phalangeal joint (Figure 5. This cut should allow full correction of the toes, and if any contrac- tures still are present in the joints, the correction can be fixed with K-wires crossing the interphalangeal joints and extended into the metatarsal joint if needed. Only 2 to 3 weeks of fixation with K-wires is necessary. If the clawed toes are cocked up with extension of the first metatarsal phalangeal joint and flexion of the interphalangeal joint, resection of the proximal interphalangeal joint usually is required. This resection is made through a middorsal incision with the joint being resected uti- lizing a rongeur. Then, the toes are corrected and fixed with K-wires for approximately 4 weeks (Figure S5. Postoperative Care No cast immobilization is needed. Medial Border Great Toenail Resection Indication This procedure is indicated if there have been repeat inflammations with an ingrown toenail. The incision is made at the medial border where the toenail flattens, going through the toenail into the distal end of the phalanx, and has Figure S5. The skin then is incised further medially, away from the border of the nail, so that it meets proximally and distally to form a wedge resection (Fig- ure S5. The wedge is removed and the base, especially proximally, is cauter- ized to kill any residual nail bed cells (Figure S5. Several sutures are used for loose approximation (Figure S5. Postoperative Care A soft dressing is used for 2 weeks. The foot is then soaked twice daily until the eschar is removed and the wound appears well healed. Robert J Petrella Search strategy Computer assisted search using Medline search systems from the last search (January 2000).