PHYSIOLOGY & BIOCHEMISTRY
►Unit 1 : Nerve and muscle
Structure of a neuron, resting membrane potential, Origin of Action potential and its propagation in myelinated and non-myelinated nerve fibres, Ultra-structure of skeletal muscle, Molecular and chemical basis of muscle contraction
Q. What do you mean by depolarization stage?
This is the stage when action potential develops in response to stimulation. Stimulation at some point of normal resting membrane leads to opening of Na+-ions through Na+ gated channels that reaches its peak very quickly (0.1ms). Normal polarized state of —90 mV is lost. With the potential rising rapidly in the positive direction. Reversal of ionic currents with positivity (+) inside and negativity (-) outside.
Q. Define neuromuscular junction.
The axon terminals of motor neurons make a specialized region of contact with the skeletal muscle fiber membrane and this region is called neuromuscular junction. Through neuromuscular transmission a nerve action potential is transformed to a muscle action potential. It is considered as a large peripheral synapse as its mechanism of operation is similar to a synapse. The neurotransmitter in these locations may be acetylcholine (ACh) or norepinephrine (NE).
►Unit 2: Digestion
SPhysiology of digestion in the alimentary canal; Absorption of carbohydrates, proteins, lipids
Q. Give a schematic presentation on disposition of short peptides in intestinal epithelial cells.
Peptides are absorbed together with a proton supplied by an apical sodium/hydrogen exchanger (NHE) by the peptide transporter 1 (PepT1). Absorbed peptides are digested by cytosolic proteases, and any amino acids that are surplus to the needs of the epithelial cell are transported into the bloodstream by a series of basolateral transport proteins.
►Unit 3: Respiration
Pulmonary ventilation, Transport of Oxygen and carbon
Q.How configuration of protein in haemoglobin helps in oxygen binding?
i)Due to the quaternary structure Hb shows close affinity to oxygen via shifting the relationship of 4 component poplypeptide chains.
ii)In relaxed or R-state it favours oxygen binding and in tense or T-state it decreases oxygen binding.
iii)Transition from one state to another involves breaking or forming of salt bridges between the polypeptide chains.
Iv)More over Fe+2 but not Fe+3 can easily release oxygen from oxy-Hb, when binds β chain comes more close together and move further apart when oxygen is detached.
►Unit 4: Cardio-vascular system
Composition of blood, Structure of Heart, Origin and conduction of the cardiac impulse, cardiac cycle
Q.What is fibrinolysis?
Fibrinolysis or the destruction of fibrin clot and many other clotting factors, occur when a plasma protein profibrinolysin (also known as Plasminogen) is activated by factor XII, lysosomal enzymes or by the vascular endothelium itself. This happens within a day or two after clotting has occurred. The profibrinolysin is activated as fibrinolysin or plasmin and it helps in dissolving the clot.
Q.What do you mean by Ventricular diastole?
The ventricles are in diastole when the two auricles are contacting and it lasts for about 0.5 seconds. The ventricular diastole is divided into 3 phases:
i) Proto-diastolic period (duration 0.04 seconds). During this phase the ventricular pressure falls rapidly and the semilunar valves close. This produces second heart sound.
ii) Isometric or Isovolumetrie relaxation period (duration 0.08 seconds). During this period the semilunar valves have closed and the A-V valves are not yet opened. So the ventricles, relax as a closed chamber. There is no change in blood volume, so it is known as isovolumetric relaxation phase. Pressure continues to decrease and when it falls below atrial pressure the A-V valves open.
iii) Filling phase. The A-V valves open and the blood start flowing from the auricles to the ventricles, During the first filling phase (duration 0.1 second) the blood flows rapidly through the A-V valves. This causes vibrations in the valves producing third heart sound. After this the flow becomes slow (duration 0.18 seconds) and this phase is known as diastasis. In the last filling stage (duration 0.1 second) the flow of blood again becomes rapid. The A-V valves vibrate due to rapid flow of blood producing fourth heart sound. The atrial and ventricular systole do not overlap but atrial diastole and ventricular diastole overlap partly.
►Unit 5: Excretion
Structure of nephron, Mechanism of Urine formation; Counter-current Mechanism
Q.What do you mean by RMIC ?
Cells in the kidneys that appear to have a secretory function include not only the granular cells in the juxtaglomerular apparatus but also some of the cells in the interstitial tissue of the medulla. These cells are called renal medullary interstitial cells (RMICs) and are specialized fibroblast-like cells .
They contain lipid droplets and are a major site of cyclooxygenase 2 (COX-2) and prostaglandin synthase (PGES) expression. PGE 2 is the major prostanoid synthesized in the kidney and is an important paracrine regulator of salt and water homeostasis. PGE 2 is secreted by the RMICs, by the macula densa, and by cells in the collecting ducts; prostacyclin (PGI 2) and other prostaglandins are secreted by the arterioles and glomeruli.
►Unit 6: Reproduction and Endocrine Glands
Physiology of male reproduction: Histology of testis, hormonal control of spermatogenesis; Physiology of female, reproduction: Histology of ovary, hormonal control of menstrual cycle. Structure and function of pituitary, thyroid, pancreas and adrenal.
Q.Briefly state the histological arrangement of sertoli cells.
The Sertoli cells are elongated pyramidal cells that are partially envelop cells of the spermatogenic lineage. The bases of the Sertoli cells adhere to the basal lamina and their apical ends frequently extend into the lumen of the seminiferous tubule. Light microscopic study revealed that the outlines of Sertoli cells appear poorly defined because of the numerous lateral processes that surround spermatogenic cells. Studies with the electron microscope reveal that these cells contain abundant smooth endoplasmic reticulum, some high RER, a well developed Golgi complex and numerous mitochondria and lysosomes. Adjacent Sertoli cells are bound together by occluding junctions at the basolateral part of the cell, forming a blood-testis barrier.
Q.Define estrous cycle.
The estrous cycle or estrous cycle is the recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases or by pregnancies. Typically, estrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation. The changes in the histology of the female reproductive organs in vertebrates occur regularly in the estrous cycle. Cyclical changes in the secretion of hormones from pituitary, gonad, uterus, etc. sponsor such changes. From the histological changes in the vaginal epithelium, different stages of the estrous cycle are identified. The vaginal epithelium is torn down and rebuilt cyclically, fluctuating between the stratified epithelium and low cuboidal epithelium.
►Unit 7: Carbohydrate Metabolism
Glycolysis, Kreb’s cycle, Glycogenesis, Electron Transport Chain.
Q.What is pentose phosphate pathway?
This is an oxidative pathway (also called hexose monophosphate pathway shunt or the phosphogluconate pathway) that operates in the cytosol of cells. This biochemical pathway is active in tissues such as the liver, adrenal cortex, testis, adipose tissue and lactating mammary glands, where fatty acids, steroids or pentoses are synthesized.
The first part of this pathway constitutes its oxidative phase which oxidizes glucose-6-phosphate into ribulose-5-phosphate with the help of NADP+ and reduces the latter to NADPH. This is followed by the nonoxidative phase which converts ribulose 5-phosphate to ribose 5-phosphate and also changes the latter and other C5 and C4 sugars into fructose 6-phosphate and glyceraldehydes 3-phosphate.
Q.What is the significance of gluconeogenesis?
It maintains the liver glycogen and a steady basal level of the blood sugar during starvation, for supplying glucose to the brain, kidneys, erythrocytes and muscles. It removes from blood the metabolites of glycolysis and lipolysis and recycles them as carbohydrates. Lactate produced by glycolysis is largely released by muscles into the blood, carried to the liver and reconverted by glycogenesis to glucose which is carried to muscles for glycolysis again.
►Unit8: Lipid Metabolism
Beta oxidation of Palmitic acid {saturated (C 16:0)} and Linoleic acid {unsaturated (C 18:2)}
Q.State the activation phase of fattyacid prior to β-oxidation.
Before the transfer into mitochondria, fatty acids need to be changed by fatty acid thiokinases (acyl-CoA synthases) into active intermediates called acyl-CoA or fatty acid- CoA thioesters. Thiokinases are C—S ligases occurring on the outer mitochondrial membrane and in the mitochondrial matrix. A thiokinase uses ATP for adenylating the fatty acid into an enzyme-bound acyl adenylate with the release of pyrophosphate.
►Unit 9: Protein Metabolism
Transamination, Deamination, Urea cycle
Q.What is transamination?
Transamination is a biochemical process of nitrogen catabolism which transfers the amino group of an amino acid (e.g., alanine) to a keto acid (e.g., α-ketoglutarate), changing the latter into a new amino acid (e.g., glutamate) and the original amino acid into a new keto acid (e.g., pyruvate).
General feature:
(1)Occurrence— Transaminase or aminotransferase catalyzes Transamination in mitochondria and cytoplasm of liver in particular and also of kidneys, hearts, testes and brain.
(2)Prosthetic group of the enzyme— Pyridoxal phosphate (PLP) acts as prosthetic group for transaminase enzyme.
(3)Restriction on enzyme activity— Mammalian transaminase acts specifically on L-amino acids, but not on their D-isomers.
(4)Limitations of transaminase activity—This enzyme activity is not applicable for some amino acids like, threonine, lysine, proline and hydroxyproline.
(5)Ping-pong type of substrate reaction— Transaminations are double-displacement type of substrate reactions. The two substrates, viz, an amino acid and an α-keto acid, bind separately and successively with the prosthetic group of the enzyme.
Q.Give full form of SGOT and SGPT.
SGOT—Serum glutamate oxaloacetate transaminase
SGPT— Serum glutamate pyruvate transaminase
►Unit 10. Enzyme
Enzyme Classification, factors affecting enzyme action, Inhibition
Q.Decode EC 3.4.11.4.
Every enzyme code consists of the letters "EC" followed by four numbers separated by periods. Those numbers represent a progressively finer classification of the enzyme. Preliminary EC numbers exist and have an 'n' as part of the fourth (serial) digit (e.g. EC 3.5.1.n3).
Tripeptide aminopeptidases have the code "EC 3.4.11.4", whose components indicate the following groups of enzymes:
EC 3 enzymes are hydrolases (enzymes that use water to break up some other molecule.
EC 3.4 are hydrolases that act on peptide bonds.
EC 3.4.11 are those hydrolases that cleave off the amino-terminal amino acid from a polypeptide.
EC 3.4.11.4 are those that cleave off the amino-terminal end from a tripeptide.
Q. What are the isozyme?
Isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes usually display different kinetic parameters (e.g. different KM values), or different regulatory properties. The existence of isozymes permits the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage. In biochemistry, isozymes (or isoenzymes) are isoforms (closely related variants) of enzymes.
Lactate dehydrogenase is a tetramer of 2 kinds of 35-kd subunits encoed by similar genes. These subunits are associated to form 5 types of tetramers (H4, H3M1, H2M2, H1M3, and M4. These species are called Isoenzyme or isozyme. [LDH1-in cardiac muscle, LDH2-in kidney, RBC etc].
Q. What is turnover number?
The turnover number of an enzyme is the number of substrate molecules converted into product by an enzyme molecule in a unit time when the enzyme is fully saturated with substrate.
It is equal to the kinetic constant k3. The maximum rate Vmax reveals the turnover number of an enzyme if the concentration of active sites [Et] is known, because Vmax = k3 [Et].
A 106M solution of carbonic anhydrase catalyses the formation of 0.6M H2CO3 per second when it is fully saturated with substrate. Hence, k3 is 6×10-5s-1. Each round of catalysis occurs in a time equal to 1/k3 which is 1.7µs for carbonic anhydrase. The turnover number of most enzymes with their physiological substrates fall in the range from 1 to 104 per second.