11. transcription: General scheme of transcription. Coding and noncoding DNA chains. RNA polymerases. Stages and enzymes of RNA synthesis. Markers of transcription: promotor, initiator, termination of transcription.

 -Transcription is the process of creating a complementary RNA copy of a sequence of DNA.During transcription, a DNA sequence is read by RNA polymerase, which produces a complementary, antiparallel RNA strand. As opposed to DNA replication, transcription results in an RNA complement that includes uracil (U) in all instances where thymine (T) would have occurred in a DNA complement.

 -Transcription can be explained easily in 4 or 5 steps, each moving like a wave along the DNA.

1.Helicase unwinds/"unzips" the DNA by breaking the hydrogen bonds between complementary nucleotides.

2.RNA nucleotides are paired with complementary DNA bases.

3.RNA sugar-phosphate backbone forms with assistance from RNA polymerase.

4.Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly synthesized RNA strand.

5/If the cell has a nucleus, the RNA is further processed (addition of a 3' poly-A tail and a 5' cap) and exits through to the cytoplasm through the nuclear pore complex.

 -Coding/Non-Coding DNA chains

When referring to DNA transcription, the coding strand is the DNA strand which has the same base sequence as the RNA transcript produced (although with thymine replaced by uracil). It is this strand which contains codons, while the non-coding strand contains anti codons.

 RNA Polymerases I,II,III,IV,V

 -Stages of Transcription(RNA synthesis):

1.Pre-initiation

2.Initiation

3.Promoter Clearance

4.Elongation

5.Termination

12. translation: Stages of Translation: 1.Initiation

The protein factors bind the small ribosomal subunit (also referred to as the 40S subunit), and these initiation factors hold the mRNA in place. START CODON: Methionine. Eukaryotic initiation factors (eIF) are proteins involved in the initiation phase of eukaryotic translation. They function in forming a complex with the 40S ribosomal subunit and Met-tRNAi called the 43S preinitation complex (PIC). 2.Elongation At the end of the initiation step, the mRNA is positioned so that the next codon can be translated during the elongation stage of protein synthesis. The initiator tRNA occupies the P site in the ribosome, and the A site is ready to receive an aminoacyl-tRNA. During chain elongation, each additional amino acid is added to the nascent polypeptide chain in a three-step microcycle. The steps in this microcycle are (1) positioning the correct aminoacyl-tRNA in the A site of the ribosome, (2) forming the peptide bond and (3) shifting the mRNA by one codon relative to the ribosome.

 

Elongation in eukaryotes is carried out with two elongation factors: eEF-1 and eEF-2.

a) The first is eEF-1, and has two subunits, α and βγ. α acts as counterpart to prokaryotic EF-Tu, mediating the entry of the aminoacyl tRNA into a free site of the ribosome. βγ acts as counterpart to prokaryotic EF-Ts, serving as the guanine nucleotide exchange factor for α, catalyzing the release of GDP from α.

b) The second elongation factor is eEF-2, the counterpart to prokaryotic EF-G, catalyzing the translocation of the tRNA and mRNA . 3.Termination Termination of elongation is dependent on eukaryotic release factors.

Eukaryotic translation termination factor 1 (eRF1), also known asTB3-1,or, eRF, which recognizes all three stop codons in place of RF1, RF2, or RF3.

13. hormones: A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism.

Hormones initiate response by affecting receptors on cell membrane ( protein hormones) or intracellular ( steroid hormones)

-For many hormones, including most protein hormones, the receptor is membrane-associated and embedded in the plasma membrane at the surface of the cell(for protein hormones)

-Some protein hormones also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism(in steroid hormones

They can do so because they are lipid-soluble. The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, effectively amplifying or suppressing the action of certain genes, and affecting protein synthesis. However, it has been shown that not all steroid receptors are located intracellularly. some are associated with the plasma membrane.

 

 Hormone-receptor complex concentrations are effectively determined by three factors:

 -The number of hormone molecules available for complex formation

-The number of receptor molecules available for complex formation

-The binding affinity between hormone and receptor.

 

 Classification:  -Peptide hormones consist of chains of amino acids. Small peptide hormones: TRH, Vasopressin

protein hormones: insulin, growth hormone glycoprotein hormones: luteinizing hormone, Follicle stimulating hormone

 -Lipid and phospholipid:derived hormones Steroid hormones: Testosterone, Cortisol

 -Monoamines derived from aromatic amino acids adrenaline, thyroxine

14. Hormones of hypothalamus: Thyrotropin-releasing hormone:  Stimulate thyroid-stimulating hormone (TSH) release from anterior pituitary (primarily). Stimulate prolactin release from anterior pituitary. Dopamine: Inhibit prolactin release from anterior pituitary Growth hormone-releasing hormone : Stimulate Growth hormone (GH) release from anterior pituitary. Somatostatin : Inhibit Growth hormone (GH) release from anterior pituitary. Inhibit thyroid-stimulating hormone (TSH) release from anterior pituitary. Gonadotropin-releasing hormone : Stimulate follicle-stimulating hormone (FSH) release from anterior pituitary. Stimulate luteinizing hormone (LH) release from anterior pituitary. Corticotropin-releasing hormone : Stimulate adrenocorticotropic hormone (ACTH) release from anterior pituitary. Oxytocin :Uterine contraction Lactation (letdown reflex). Vasopressin : Increase in the permeability to water of the cells of distal tubule and collecting duct in the kidney and thus allows water reabsorption and excretion of concentrated urine

15. Mechanism of hormonal action: Most hormones initiate a cellular response by initially combining with either a specific intracellular or cell membrane associated receptor protein. A cell may have several different receptors that recognize the same hormone and activate different signal transduction pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway.

 

For many hormones, including most protein hormones, the receptor is membrane-associated and embedded in the plasma membrane at the surface of the cell. The interaction of hormone and receptor typically triggers a cascade of secondary effects within the cytoplasm of the cell, often involving phosphorylation or dephosphorylation of various other cytoplasmic proteins, changes in ion channel permeability, or increased concentrations of intracellular molecules that may act as secondary messengers (e.g., cyclic AMP). Some protein hormones also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.

 

An important consideration, dictating the level at which cellular signal transduction pathways are activated in response to a hormonal signal, is the effective concentration of hormone-receptor complexes that are formed. Hormone-receptor complex concentrations are effectively determined by three factors:

16. Hormones of anterior pituitary gland: Growth hormone (somatotropin), release under influence of hypothalamic GHRH; inhibited by hypothalamic Somatostatin. !! Prolonged GH excess thickens the bones of the jaw, fingers and toes. Resulting heaviness of the jaw and increased size of digits is referred to as acromegaly. Accompanying problems can include sweating, pressure on nerves, muscle weakness, excess sex hormone-binding globulin, insulin resistance or even a rare form of type 2 diabetes, and reduced sexual function.

~The effects of growth hormone deficiency vary depending on the age at which they occur. In children, growth failure and short stature are the major manifestations of GH deficiency, with common causes including genetic conditions and congenital malformations. It can also cause delayed sexual maturity !!

Prolactin release under influence of multiple hypothalamic (PRH). !! Hyperprolactinaemia is associated with hypoestrogenism, anovulatory infertility, oligomenorrhoea, amenorrhoea, unexpected lactation, and loss of libido in women, and erectile dysfunction and loss of libido in  !! Hypoprolactinemia, or serum prolactin deficiency, is associated with ovarian dysfunction in women, and metabolic syndrome, anxiety, arteriogenic erectile dysfunction, premature ejaculation,oligozoospermia, asthenospermia, hypofunction of seminal vesicles, and hypoandrogenism in men. In one study, normal sperm characteristics were restored when prolactin levels were brought up to normal values in hypoprolactinemic me !!

17. Hormones of posterior pituitary gland: Arginine vasopressin (AVP), is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's permeability. . It plays a key role in homeostasis. One of the most important roles of AVP is to regulate the body's retention of water; it is released when the body is dehydrated and causes the kidneys to conserve water, thus concentrating the urine, and reducing urine volume. In high concentrations, it also raises blood pressure by inducing moderate vasoconstriction. 1) Increase in the permeability to water of the cells of distal tubule and collecting duct in the kidney 2) Increase in the permeability of the inner medullary portion of the collecting duct to urea, allowing increased reabsorption of urea into the medullary interstitium, down the concentration gradient . 3) Vasopressin increases peripheral vascular resistance and thus increases arterial blood pressure.

 Vasopressin is secreted from the posterior pituitary gland in response to reductions in plasma volume, in response to increases in the plasma osmolality, and in response to cholecystokinin secreted by the small intestine.

The vasopressins are peptides consisting of nine amino acids (nonapeptides). . The amino acid sequence of arginine vasopressin is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly, with the cysteine residues forming a sulfur bridge. Lysine vasopressin has a lysine in place of the arginine.

 

Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain. Also known as alpha-hypophamine (α–hypophamine). Oxytocin is best known for its roles in female reproduction. It is released in large amounts 1) after distension of the cervix and uterus during labor, and 2) after stimulation of the nipples, facilitating birth and breastfeeding. Oxytocin is a peptide of nine amino acids (a nonapeptide). Its systematic name is cysteine-tyrosine-isoleucine-glutamine-asparagine-cysteine-proline-leucine-glycine-amine (cys–tyr–ile–gln–asn–cys–pro–leu–gly- NH2, or (CYIQNCPLG-NH2). The cysteine residues form a disulfide bond. Oxytocin has a molecular mass of 1007 daltons.

Actions: Letdown Reflex, Uterine Contraction, reduction of urination, Modulation of hypothalamic-pituitary-adrenal axis activity, Autism, Increasing trust and reducing fear, Bonding, sexual arousal, maternal behavior

18. Hormones of pancreatic gland: INSULIN:   Actions:   The actions of insulin on the global human metabolism level include: Control of cellular intake of certain substances, most prominently glucose in muscle and adipose tissue (about two-thirds of body cells) Increase of DNA replication and protein synthesis via control of amino acid uptake Modification of the activity of numerous enzymes The actions of insulin (indirect and direct) on cells include: Increased glycogen synthesis – insulin forces storage of glucose in liver (and muscle) cells in the form of glycogen; lowered levels of insulin cause liver cells to convert glycogen to glucose and excrete it into the blood. This is the clinical action of insulin, which is directly useful in reducing high blood glucose levels as in diabetes. Increased lipid synthesis – insulin forces fat cells to take in blood lipids, which are converted to triglycerides; lack of insulin causes the reverse. Increased esterification of fatty acids – forces adipose tissue to make fats (i.e., triglycerides) from fatty acid esters; lack of insulin causes the reverse. Decreased proteolysis – decreasing the breakdown of protein Decreased lipolysis – forces reduction in conversion of fat cell lipid stores into blood fatty acids; lack of insulin causes the reverse. Decreased gluconeogenesis – decreases production of glucose from nonsugar substrates, primarily in the liver (the vast majority of endogenous insulin arriving at the liver never leaves the liver); lack of insulin causes glucose production from assorted substrates in the liver and elsewhere. Decreased autophagy - decreased level of degradation of damaged organelles. Postprandial levels inhibit autophagy completely. Increased amino acid uptake – forces cells to absorb circulating amino acids; lack of insulin inhibits absorption. Increased potassium uptake – forces cells to absorb serum potassium; lack of insulin inhibits absorption. Insulin's increase in cellular potassium uptake lowers potassium levels in blood. This possible occurs via insulin-induced translocation of the Na+/K+-ATPase to the surface of skeletal muscle cells. Arterial muscle tone – forces arterial wall muscle to relax, increasing blood flow, especially in microarteries; lack of insulin reduces flow by allowing these muscles to contract. Increase in the secretion of hydrochloric acid by parietal cells in the stomach Decreased renal sodium excretion.  Insulin is produced in the pancreas and released when any of several stimuli are detected. These stimuli include ingested protein and glucose in the blood produced from digested food.     In β-cells, insulin is synthesized from the proinsulin precursor molecule by the action of proteolytic enzymes, known asprohormone convertases (PC1 and PC2), as well as the exoproteasecarboxypeptidase E. The endogenous production of insulin is regulated in several steps along the synthesis pathway: At transcription from the insulin gene In mRNA stability At the mRNA translation In the posttranslational modifications     Beta cells in the islets of Langerhans release insulin in two phases. The first phase release is rapidly triggered in response to increased blood glucose levels. The second phase is a sustained, slow release of newly formed vesicles triggered independently of sugar.

19. Catecholamines: are "fight-or-flight" hormones released by the adrenal glands in response to stress. They are part of the sympathetic nervous system. They are called catecholamines because they contain a catechol or 3,4-dihydroxyphenyl group. They are derived from the amino acid tyrosine. In the human body, the most abundant catecholamines are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine, all of which are produced from phenylalanineand tyrosine. Various stimulant drugs are catecholamine analogs. Catecholamines are water-soluble and are 50% bound to plasma proteins, so they circulate in the bloodstream. Tyrosine is created from phenylalanine by hydroxylation by the enzyme phenylalanine hydroxylase. (Tyrosine is also ingested directly from dietary protein). It is then sent to catecholamine-secreting neurons. Here, several reactions serially convert tyrosine to L-DOPA, to dopamine, to norepinephrine, and eventually to epinephrine.     Dopamine is the first catecholamine synthesized from DOPA. In turn, norepinephrine and epinephrine are derived from further metabolic modification of dopamine. The enzyme dopamine hydroxylase requires copper as a cofactor and DOPA decarboxylase requires PLP. The rate limiting step in catecholamine biosynthesis is hydroxylation of tyrosine.     Catecholamine synthesis is inhibited by alpha-methyl-p-tyrosine (AMPT), which inhibits tyrosine hydroxylase.     Catecholamines cause general physiological changes that prepare the body for physical activity (fight-or-flight response). Some typical effects are increases in heart rate, blood pressure, blood glucoselevels, and a general reaction of the sympathetic nervous system.     Two catecholamines, norepinephrine and dopamine, act as neuromodulators in the central nervous system and as hormones in the blood circulation.

20. Steroids of suprarenal glands: Glucocorticoids (GC) are a class of steroid hormones that bind to the glucocorticoid receptor (GR), which is present in almost every vertebrate animal cell. The name glucocorticoid derives from their role in the regulation of the metabolism of glucose, GCs are part of the feedback mechanism in the immune system that turns immune activity (inflammation) down. They are therefore used in medicine to treat diseases that are caused by an overactive immune system, such as allergies, asthma, autoimmune diseases and sepsis. Glucocorticoids are distinguished from mineralocorticoids and sex steroids by their specific receptors, target cells, and effects. Cortisol (or hydrocortisone) is the most important human glucocorticoid. It is essential for life, and it regulates or supports a variety of importantncardiovascular, metabolic, immunologic, and homeostatic functions. Glucocorticoid effects may be broadly classified into two major categories: immunological and metabolic. In addition, glucocorticoids play important roles in fetal development.     Up-regulate the expression of anti-inflammatory proteins     Down-regulate the expression of pro-inflammatory proteins Glucocorticoids are also shown to play a role in the development and homeostasis of T lymphocytes.   Metabolic effects: Stimulation of gluconeogenesis, in particular, in the liver: This pathway results in the synthesis of glucose from non-hexosesubstrates such as amino acids and glycerol from triglyceride breakdown, and is particularly important in carnivores and certain herbivores. Enhancing the expression of enzymes involved in gluconeogenesis is probably the best-known metabolic function of glucocorticoids. Mobilization of amino acids from extrahepatic tissues: These serve as substrates for gluconeogenesis. Inhibition of glucose uptake in muscle and adipose tissue: A mechanism to conserve glucose. Stimulation of fat breakdown in adipose tissue: The fatty acids released by lipolysis are used for production of energy in tissues like muscle, and the released glycerol provide another substrate for gluconeogenesis.   Glucocorticoids not only suppress immune response, but also inhibit the two main products of inflammation, prostaglandins and leukotrienes. Glucocorticoids inhibit prostaglandin synthesis at the level of phospholipase A2 as well as at the level of cyclooxygenase/PGE isomerase (COX-1 and COX-2), the. In addition, glucocorticoids also suppress cyclooxygenase expression.   Cushing Syndrome : Hormones that come from outside the body are called exogenous; hormones that come from within the body are called endogenous. The most common cause of Cushing's syndrome is exogenous administration of glucocorticoids prescribed by a health care practitioner to treat other diseases (called iatrogenic Cushing's syndrome). Cushing's syndrome can also be due to the use of medroxyprogesterone Endogenous Cushing's syndrome results from some derangement of the body's own system of secreting cortisol. In pituitary Cushing's, a benign pituitary adenoma secretes ACTH. This is also known as Cushing's disease and is responsible for 70% of endogenous Cushing's syndrome. In adrenal Cushing's, excess cortisol is produced by adrenal gland tumors, hyperplastic adrenal glands, or adrenal glands with nodular adrenal hyperplasia. Finally, tumors outside the normal pituitary-adrenal system can produce ACTH that affects the adrenal glands.