NEET MDS Biochemistry Syllabus

Explain the 'induced fit' model of enzyme action.

Substrate binding induces a conformational change in the active site so it molds around the substrate, optimizing catalysis (Koshland's model), unlike the rigid lock-and-key model.

What does the Michaelis-Menten constant (Km) represent?

Km is the substrate concentration at which reaction velocity is half of Vmax; a low Km indicates high enzyme-substrate affinity.

How do competitive and non-competitive inhibitors affect Km and Vmax?

Competitive: increases Km, Vmax unchanged. Non-competitive: Km unchanged, Vmax decreased.

How do temperature and pH affect enzyme activity?

Activity rises with temperature up to an optimum (~37°C) then falls due to denaturation; each enzyme has an optimum pH (e.g., pepsin ~2, alkaline phosphatase ~9) beyond which activity declines.

What is the difference between zero-order and first-order enzyme kinetics?

Zero-order: rate is independent of substrate concentration (enzyme saturated, at Vmax). First-order: rate is directly proportional to substrate concentration (low substrate).

How are carbohydrates classified?

Monosaccharides (glucose, fructose), disaccharides (sucrose, lactose, maltose), oligosaccharides, and polysaccharides (starch, glycogen, cellulose).

What is the net ATP yield of glycolysis and where does it occur?

Glycolysis occurs in the cytoplasm and yields a net 2 ATP and 2 NADH per glucose molecule, converting glucose to 2 pyruvate.

What is the role of the TCA (Krebs) cycle and where does it occur?

In the mitochondrial matrix, the TCA cycle oxidizes acetyl-CoA to CO2, producing 3 NADH, 1 FADH2, and 1 GTP per turn for energy generation.

How many ATP are produced from the complete oxidation of one glucose molecule?

Approximately 30-32 ATP (modern estimate) via glycolysis, TCA cycle, and oxidative phosphorylation.

What is the function of glycogenesis and glycogenolysis?

Glycogenesis = synthesis of glycogen from glucose (storage); glycogenolysis = breakdown of glycogen to release glucose, regulated by insulin (storage) and glucagon/epinephrine (breakdown).

What is gluconeogenesis and where does it occur?

Synthesis of glucose from non-carbohydrate sources (lactate, glycerol, glucogenic amino acids), mainly in the liver (and kidney) during fasting.

What is the main purpose of the HMP shunt (pentose phosphate pathway)?

To produce NADPH (for biosynthesis and antioxidant defense) and ribose-5-phosphate (for nucleotide synthesis); no ATP is generated.

How is blood glucose hormonally regulated?

Insulin lowers blood glucose (promotes uptake, glycogenesis); glucagon, epinephrine, cortisol, and growth hormone raise it (glycogenolysis, gluconeogenesis).

What are the clinical features of diabetes mellitus biochemically?

Hyperglycemia, glycosuria, ketonemia/ketonuria, polyuria, polydipsia, and elevated HbA1c due to insulin deficiency or resistance.

How are lipids classified?

Simple lipids (fats, oils, waxes), compound lipids (phospholipids, glycolipids, lipoproteins), and derived lipids (fatty acids, steroids, ketone bodies).

Where does fatty acid beta-oxidation occur and what does it yield?

In the mitochondrial matrix; each cycle removes 2 carbons producing 1 acetyl-CoA, 1 FADH2, and 1 NADH.

What are the three ketone bodies and when are they formed?

Acetoacetate, beta-hydroxybutyrate, and acetone; formed in the liver during starvation, fasting, or uncontrolled diabetes when fatty acid oxidation exceeds carbohydrate availability.

List the major lipoproteins in order of increasing density.

Chylomicrons, VLDL, IDL, LDL, HDL (density increases as protein content rises and lipid falls).

Why is LDL called 'bad' and HDL 'good' cholesterol?

LDL delivers cholesterol to tissues and promotes atherosclerosis; HDL performs reverse cholesterol transport, removing cholesterol from tissues to the liver.

What is the building block of DNA and its components?

The nucleotide: a nitrogenous base + deoxyribose sugar + phosphate group. Bases are adenine, guanine (purines), cytosine, thymine (pyrimidines).

Describe the Watson-Crick model of DNA structure.

A right-handed antiparallel double helix with a sugar-phosphate backbone; bases pair via H-bonds (A=T with 2 bonds, G≡C with 3 bonds) following Chargaff's rule.

What is the central dogma of molecular biology?

DNA → (transcription) → RNA → (translation) → Protein; information flows from DNA to RNA to protein (with reverse transcription as an exception).

Compare DNA and RNA.

DNA: deoxyribose, double-stranded, thymine, stores genetic info. RNA: ribose, usually single-stranded, uracil instead of thymine, involved in protein synthesis.

What are the three main types of RNA and their functions?

mRNA carries genetic code to ribosomes; tRNA brings amino acids during translation; rRNA forms the structural/catalytic core of ribosomes.

What is gene expression and its two main steps?

The process by which genetic information is used to synthesize a functional product (protein). Steps: transcription (DNA→mRNA) and translation (mRNA→protein).

List the fat-soluble vitamins and one deficiency disease for each.

A (night blindness/xerophthalmia), D (rickets/osteomalacia), E (hemolytic anemia/neuropathy), K (bleeding/poor clotting).

List the water-soluble vitamins and a key deficiency.

B1 (beriberi), B2, B3/niacin (pellagra), B5, B6, B7/biotin, B9/folate (megaloblastic anemia/neural tube defects), B12 (pernicious anemia), and C (scurvy).

Why is vitamin C important for dental and connective tissue health?

Vitamin C is a cofactor for prolyl/lysyl hydroxylase needed for collagen synthesis; deficiency causes scurvy with bleeding gums, poor wound healing, and weak dentin/bone.

What is the role of vitamin D and calcium/phosphate in mineralization?

Vitamin D (calcitriol) promotes intestinal absorption of calcium and phosphate, maintaining serum levels needed for hydroxyapatite formation in bones and teeth.

Name key macrominerals and trace elements and a function of each.

Macrominerals: calcium and phosphorus (bone/tooth mineralization), sodium/potassium (fluid balance). Trace: iron (hemoglobin), iodine (thyroid hormones), fluoride (enamel resistance to caries), zinc (enzyme cofactor).

What is BMR and how is energy balance defined?

Basal Metabolic Rate is the energy expended at complete rest to maintain vital functions. Energy balance = energy intake vs expenditure; positive balance causes weight gain, negative balance causes weight loss.