Tamil Nadu HSE Second Year Biochemistry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Anomeric carbon

The carbonyl carbon of a monosaccharide that becomes a new chiral centre on ring closure; if free, it allows the sugar to reduce Benedict's reagent.

Essential amino acids

Nine amino acids humans cannot synthesize in adequate amounts: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine; they must come from diet.

Competitive inhibition

An inhibitor resembling the substrate binds the active site reversibly, raising apparent Km while Vmax stays unchanged; adding more substrate overcomes the inhibition.

Km

The Michaelis constant is the substrate concentration giving half of Vmax. A low Km means the enzyme reaches half-maximal velocity at low substrate, indicating high affinity.

Zymogen

An inactive enzyme precursor activated by limited proteolysis, such as trypsinogen cleaved to trypsin by enteropeptidase, preventing premature digestion of the secreting tissue.

Chemiosmotic coupling

Electron transport pumps protons across the inner mitochondrial membrane; the resulting gradient drives ATP synthase to phosphorylate ADP, linking oxidation to phosphorylation.

Uncoupler

A substance such as 2,4-dinitrophenol that carries protons across the inner mitochondrial membrane, dissipating the gradient so oxygen consumption rises while ATP synthesis falls.

P/O ratio

Molecules of ATP formed per pair of electrons passing to oxygen; about 2.5 for NADH and 1.5 for FADH2 in current accounting.

Substrate-level phosphorylation

ATP formation by direct transfer of a phosphate group from a high-energy substrate to ADP, as in glycolysis and the succinyl-CoA synthetase step of the TCA cycle.

Phosphofructokinase-1

The rate-limiting enzyme of glycolysis, converting fructose-6-phosphate to fructose-1,6-bisphosphate; activated by AMP and fructose-2,6-bisphosphate, inhibited by ATP and citrate.

Gluconeogenesis

Synthesis of glucose from non-carbohydrate precursors such as lactate, glycerol, and glucogenic amino acids, occurring mainly in liver and kidney cortex with four unique enzymes.

HMP shunt

The pentose phosphate pathway generates NADPH and ribose-5-phosphate; glucose-6-phosphate dehydrogenase is the regulated enzyme, and NADPH maintains reduced glutathione.

Carnitine shuttle

CPT-I converts acyl-CoA to acylcarnitine for entry into mitochondria, and CPT-II regenerates acyl-CoA inside; this is the rate-limiting step of fatty acid oxidation.

Ketogenesis

Formation of acetoacetate, beta-hydroxybutyrate, and acetone from acetyl-CoA in liver mitochondria, occurring when oxaloacetate is depleted during starvation or uncontrolled diabetes.

HMG-CoA reductase

The rate-limiting enzyme of cholesterol synthesis converting HMG-CoA to mevalonate; it is inhibited by statins and regulated by feedback and SREBP transcription factors.

Transamination

Transfer of an amino group from an amino acid to alpha-ketoglutarate to form glutamate, catalyzed by aminotransferases such as ALT and AST, which require pyridoxal phosphate.

Urea cycle

Hepatic pathway converting ammonia to urea through carbamoyl phosphate, citrulline, and argininosuccinate; it consumes three ATP and produces urea and fumarate.

Nitrogen balance

The difference between nitrogen intake and excretion; positive in growth and pregnancy, negative in starvation, trauma, and uncontrolled diabetes.

Semi-conservative replication

Each daughter DNA molecule contains one parental strand and one newly synthesized strand, established by the Meselson-Stahl experiment and mediated by DNA polymerase and ligase.

Lesch-Nyhan syndrome

X-linked deficiency of HGPRT impairing purine salvage, causing hyperuricaemia, gout, intellectual disability, and compulsive self-mutilation.

RNA polymerase II

The eukaryotic enzyme that transcribes messenger RNA; it requires the TATA-binding protein and general transcription factors and is inhibited by alpha-amanitin.

Start codon

AUG codes for methionine and initiates translation; the stop codons UAA, UAG, and UGA terminate translation and do not code for any amino acid.

Vitamin K

A fat-soluble vitamin required for gamma-carboxylation of glutamate residues in clotting factors II, VII, IX, and X; deficiency prolongs prothrombin time.

Pellagra

Niacin deficiency causing dermatitis, diarrhoea, and dementia; tryptophan can be converted to niacin at 60 mg tryptophan per 1 mg niacin equivalent.

Megaloblastic anaemia

Anaemia with large nucleated red cell precursors caused by vitamin B12 or folate deficiency impairing DNA synthesis; B12 deficiency also causes neurological damage.

Insulin

A pancreatic beta-cell hormone that lowers blood glucose by promoting GLUT4-mediated uptake in muscle and fat and stimulating glycogen synthesis, lipogenesis, and protein synthesis.

Glucagon

A pancreatic alpha-cell hormone that raises blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis; it is counter-regulatory to insulin.

Thyroid hormones

T4 and T3 from the thyroid gland increase basal metabolic rate and thermogenesis; T4 is converted to the more active T3 in peripheral tissues.

HbA1c

Glycated haemoglobin reflecting average blood glucose over about two to three months; a value of 6.5 percent or more is diagnostic of diabetes mellitus.

Liver function tests

A panel including ALT, AST, alkaline phosphatase, bilirubin, albumin, and prothrombin time; ALT is more liver-specific, and alkaline phosphatase rises in biliary obstruction.

Troponin I and T

Cardiac proteins released into blood after myocardial infarction; they are the most specific markers and remain elevated for several days after the event.

Creatinine clearance

A measure of glomerular filtration rate calculated from urine and serum creatinine; creatinine is preferred over urea because it is less affected by diet.