Tamil Nadu HSE First Year Biochemistry flashcards

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

Zwitterion

An amino acid form carrying both a positive (NH3+) and a negative (COO-) group at the same time; it predominates near neutral pH and gives amino acids their amphoteric, buffering behaviour.

Isoelectric point (pI)

The pH at which an amino acid or protein has zero net charge, so it does not migrate in an electric field and is least soluble; for a neutral amino acid pI equals the mean of its two pKa values.

Peptide bond

A covalent amide linkage formed between the alpha-carboxyl group of one amino acid and the alpha-amino group of the next, with loss of water; it is planar and rigid due to partial double-bond character.

Protein denaturation

Loss of the secondary, tertiary and quaternary structure of a protein by heat, extremes of pH or chemicals, without breaking peptide bonds; biological activity is usually destroyed while the primary sequence remains intact.

Michaelis constant Km

The substrate concentration at which an enzyme works at half its maximum velocity; a low Km indicates high affinity of the enzyme for its substrate, and it is expressed in concentration units.

Competitive inhibition

An inhibitor resembling the substrate binds the active site, raising the apparent Km while leaving Vmax unchanged; the inhibition is overcome by increasing substrate concentration, as with statins and HMG-CoA reductase.

Lineweaver-Burk plot

A double-reciprocal graph of 1/v against 1/[S] that is linear; its y-intercept gives 1/Vmax and its x-intercept gives -1/Km, making inhibition patterns easy to distinguish.

Holoenzyme

The complete, catalytically active enzyme formed by the apoenzyme (protein part) combined with its required cofactor or coenzyme, such as a metal ion or NAD+, needed for activity.

Reducing sugar

A sugar with a free anomeric carbon that can reduce cupric ions in Benedict's or Fehling's reagent to red cuprous oxide; glucose, fructose, maltose and lactose are reducing, sucrose is not.

Glycosidic bond

The covalent bond joining two monosaccharides through the anomeric carbon of one and a hydroxyl group of the other, with loss of water; its alpha or beta configuration determines digestibility.

Mutarotation

The spontaneous change in optical rotation of a sugar solution as alpha and beta anomers interconvert through the open-chain form until equilibrium is reached, typical of glucose and other reducing sugars.

Amylose and amylopectin

The two components of starch: amylose is an unbranched alpha-1,4 glucose chain, while amylopectin is branched through alpha-1,6 linkages; both are digested by amylase to maltose.

Essential fatty acids

Fatty acids humans cannot synthesise because they lack the required desaturase enzymes: linoleic acid (omega-6) and alpha-linolenic acid (omega-3); they must be supplied by diet for membrane and eicosanoid synthesis.

Iodine value

The number of grams of iodine absorbed by 100 g of a fat or oil; it measures the degree of unsaturation, so drying oils with many double bonds have high iodine values.

Phospholipid bilayer

A membrane structure formed by amphipathic phospholipids, with hydrophilic phosphate heads facing water on both sides and hydrophobic fatty acid tails buried inside; it is the basic framework of cell membranes.

Saponification

Alkaline hydrolysis of a triacylglycerol yielding glycerol and the sodium or potassium salts of fatty acids (soap); the saponification number reflects average fatty acid chain length.

Chargaff's rules

In double-stranded DNA the amount of adenine equals thymine and guanine equals cytosine, so purines equal pyrimidines; base composition varies between species but is constant within one species.

Semi-conservative replication

The mode of DNA replication in which the double helix unwinds and each parental strand serves as a template, so every daughter molecule contains one old and one newly synthesised strand.

Codon and anticodon

A codon is a triplet of mRNA bases specifying one amino acid; the anticodon is the complementary triplet on tRNA that pairs with it during translation at the ribosome.

Phosphodiester bond

The linkage joining nucleotides in DNA and RNA, formed between the 3'-hydroxyl of one sugar and the phosphate attached to the 5' carbon of the next; it gives the backbone its directionality.

Coenzyme A

A pantothenic acid (vitamin B5) derivative that carries acyl groups; acetyl-CoA is the central entry point of acetyl units into the citric acid cycle and fatty acid synthesis.

Pellagra

Niacin (vitamin B3) deficiency disease characterised by the three Ds: dermatitis, diarrhoea and dementia; it occurs where maize, low in available niacin and tryptophan, is the staple food.

Thiamine pyrophosphate (TPP)

The active coenzyme form of vitamin B1, required for oxidative decarboxylation of alpha-keto acids such as pyruvate and alpha-ketoglutarate; deficiency causes beriberi and Wernicke encephalopathy.

Trace elements

Minerals needed in very small amounts, including iron, zinc, copper, iodine, selenium, manganese and fluoride; each serves as a cofactor or component of specific enzymes and hormones.

ATP hydrolysis

Cleavage of the terminal phosphoanhydride bond of ATP to ADP and inorganic phosphate, releasing about 7.3 kcal/mol under standard conditions; this energy drives endergonic cellular reactions.

Beta-oxidation

Mitochondrial pathway that shortens a fatty acyl-CoA by two carbons per cycle, releasing acetyl-CoA plus one NADH and one FADH2, the main route of fatty acid energy production.

Gluconeogenesis

Synthesis of glucose from non-carbohydrate precursors such as lactate, glycerol and amino acids, occurring mainly in liver and kidney and using four enzymes that bypass irreversible glycolytic steps.

Oxidative phosphorylation

ATP synthesis driven by the proton gradient generated as electrons pass from NADH or FADH2 along the respiratory chain to oxygen, catalysed by ATP synthase in the inner mitochondrial membrane.

Beer-Lambert law

Absorbance of a solution equals molar absorptivity times concentration times path length; it is the basis of colorimetric estimation, where absorbance is proportional to the concentration of the coloured substance.

Friedewald formula

A calculation of LDL cholesterol as total cholesterol minus HDL cholesterol minus triglycerides divided by 5, valid only when triglycerides are below about 400 mg/dL.

Glycated haemoglobin (HbA1c)

Haemoglobin with glucose non-enzymatically attached, reflecting average blood glucose over the preceding two to three months; it is used to monitor long-term glycaemic control in diabetes.

Electrophoresis

A technique separating charged molecules such as proteins or nucleic acids in an electric field according to their charge-to-mass ratio, commonly on agarose or polyacrylamide gels.