NEET PG Bio Chemistry Syllabus

How do enzymes increase reaction rate thermodynamically?

They lower the activation energy (Ea) of a reaction without changing the equilibrium or the free energy (delta G) of the overall reaction.

State the Michaelis-Menten equation and what Km represents.

v = (Vmax * [S]) / (Km + [S]). Km is the substrate concentration at half-maximal velocity; it inversely reflects enzyme affinity for substrate (low Km = high affinity).

How does competitive inhibition affect Km and Vmax?

Competitive inhibition increases (apparent) Km but Vmax is unchanged, because the inhibitor competes at the active site and can be overcome by excess substrate.

How does non-competitive inhibition affect Km and Vmax?

Non-competitive inhibition decreases Vmax but Km is unchanged, because the inhibitor binds an allosteric site and cannot be overcome by adding more substrate.

What is the net ATP yield and end product of glycolysis under aerobic conditions?

Net 2 ATP and 2 NADH per glucose, producing 2 pyruvate. (4 ATP made, 2 consumed.)

Which enzyme is the rate-limiting (committed) step of glycolysis and how is it regulated?

Phosphofructokinase-1 (PFK-1). Activated by AMP and fructose-2,6-bisphosphate; inhibited by ATP and citrate.

What are the three irreversible enzymes of glycolysis?

Hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase.

Which gluconeogenesis enzymes bypass the irreversible steps of glycolysis?

Pyruvate carboxylase + PEP carboxykinase (bypass pyruvate kinase), fructose-1,6-bisphosphatase (bypasses PFK-1), and glucose-6-phosphatase (bypasses hexokinase).

What are the two major products of the Pentose Phosphate Pathway and their uses?

NADPH (for reductive biosynthesis and antioxidant defense via glutathione) and ribose-5-phosphate (for nucleotide synthesis).

Which enzyme is rate-limiting in the Pentose Phosphate Pathway, and what disease results from its deficiency?

Glucose-6-phosphate dehydrogenase (G6PD); deficiency causes hemolytic anemia, especially with oxidative stress (drugs, fava beans, infection).

Which enzymes synthesize and degrade glycogen, and which is the rate-limiting step of each?

Synthesis: glycogen synthase (rate-limiting). Degradation: glycogen phosphorylase (rate-limiting). Branching by branching enzyme; debranching by debranching enzyme.

Name the deficient enzyme in von Gierke disease (Type I glycogen storage disease).

Glucose-6-phosphatase deficiency; causes severe fasting hypoglycemia and hepatomegaly.

How many ATP/GTP, NADH, and FADH2 are produced per turn of the Citric Acid Cycle?

Per turn: 3 NADH, 1 FADH2, 1 GTP (or ATP), and 2 CO2 released. (Net ~10 ATP per acetyl-CoA.)

What is the rate-limiting enzyme of the Citric Acid Cycle?

Isocitrate dehydrogenase (the major rate-limiting step); regulated allosterically by ADP/NAD+ (activate) and ATP/NADH (inhibit).

What is the rate-limiting enzyme of fatty acid synthesis and how is it regulated?

Acetyl-CoA carboxylase (ACC), which makes malonyl-CoA. Activated by citrate and insulin; inhibited by palmitoyl-CoA and glucagon/epinephrine.

What molecule shuttles long-chain fatty acids into the mitochondria for beta-oxidation, and what inhibits this shuttle?

Carnitine (via carnitine palmitoyltransferase I, CPT-I). Malonyl-CoA inhibits CPT-I, preventing simultaneous synthesis and oxidation.

What products are generated per cycle of fatty acid beta-oxidation?

Each cycle removes 2 carbons producing 1 acetyl-CoA, 1 NADH, and 1 FADH2.

Which enzyme is rate-limiting for triacylglycerol mobilization from adipose tissue?

Hormone-sensitive lipase (and adipose triglyceride lipase); activated by glucagon/epinephrine and inhibited by insulin.

Match the major lipoproteins to their primary function: chylomicrons, VLDL, LDL, HDL.

Chylomicrons carry dietary (exogenous) TAG; VLDL carries endogenous TAG from liver; LDL delivers cholesterol to tissues ('bad'); HDL performs reverse cholesterol transport from tissues to liver ('good').

What enzyme on capillary endothelium hydrolyzes triacylglycerols in chylomicrons and VLDL, and what activates it?

Lipoprotein lipase (LPL); activated by apolipoprotein C-II and insulin.

Name the three ketone bodies and where they are synthesized.

Acetoacetate, beta-hydroxybutyrate, and acetone; synthesized in the liver mitochondria (ketogenesis). The rate-limiting enzyme is HMG-CoA synthase.

Why can the liver produce but not use ketone bodies?

The liver lacks thiophorase (succinyl-CoA:acetoacetate CoA transferase), the enzyme needed to convert acetoacetate back to acetoacetyl-CoA for utilization.

What are transamination and deamination in amino acid metabolism?

Transamination transfers an amino group to a keto acid (e.g., by ALT/AST using pyridoxal phosphate). Oxidative deamination (glutamate dehydrogenase) removes the amino group as free ammonia (NH3).

Which amino acids are purely ketogenic?

Leucine and lysine are exclusively ketogenic; they cannot form glucose.

What enzyme deficiency causes phenylketonuria (PKU) and what accumulates?

Phenylalanine hydroxylase deficiency; phenylalanine accumulates and is converted to phenylketones, causing intellectual disability if untreated.

What is the role of tetrahydrofolate (THF) in one-carbon metabolism?

THF carries and transfers one-carbon units (methyl, methylene, formyl) for synthesis of purines, thymidylate (dTMP), and methionine regeneration.

What is the chemiosmotic theory of ATP synthesis?

The electron transport chain pumps protons across the inner mitochondrial membrane creating an electrochemical gradient; the proton-motive force drives ATP synthase (Complex V) to produce ATP.

How does the ATP/ADP ratio regulate oxidative phosphorylation (respiratory control)?

High ADP (low ATP) stimulates oxidative phosphorylation; high ATP and low ADP slow it. ADP availability is the primary controller (respiratory/acceptor control).

How do uncouplers like 2,4-dinitrophenol or thermogenin affect oxidative phosphorylation?

They dissipate the proton gradient, uncoupling electron transport from ATP synthesis, so energy is released as heat instead of ATP.

Why do mitochondrial disorders preferentially affect high-energy tissues, and how are they inherited?

Tissues like brain, muscle, heart depend heavily on oxidative phosphorylation, so defects in mtDNA-encoded ETC components impair them most. mtDNA is maternally inherited and shows heteroplasmy with threshold effect.

What are the three chemical classes of hormones with examples?

1) Peptide/protein (insulin, glucagon), 2) Steroid (cortisol, estrogen, from cholesterol), 3) Amino acid derivatives (thyroid hormones, catecholamines).

Compare the signal transduction of steroid hormones versus peptide hormones.

Steroid (lipophilic) hormones cross the membrane and bind intracellular/nuclear receptors to alter gene transcription. Peptide (hydrophilic) hormones bind cell-surface receptors and act via second messengers (cAMP, IP3/DAG, Ca2+).

In the cAMP second-messenger pathway, what is the sequence from hormone to effect?

Hormone binds GPCR -> activates Gs protein -> activates adenylate cyclase -> increases cAMP -> activates protein kinase A (PKA) -> phosphorylates target proteins.

List the water-soluble vitamins and a key role of one of them.

B-complex (B1, B2, B3, B5, B6, B7, B9, B12) and vitamin C. Example: vitamin B1 (thiamine) is a cofactor (TPP) for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Match vitamin deficiencies: scurvy, beriberi, pellagra, rickets.

Scurvy = vitamin C; Beriberi = thiamine (B1); Pellagra = niacin (B3, the 3 D's: dermatitis, diarrhea, dementia); Rickets = vitamin D.

Which vitamin deficiency causes megaloblastic anemia, and which additionally causes neurological symptoms?

Both folate (B9) and vitamin B12 deficiency cause megaloblastic anemia, but only B12 deficiency causes neurological symptoms (subacute combined degeneration).

What is the principle of separating proteins by SDS-PAGE?

SDS denatures proteins and gives them uniform negative charge; in polyacrylamide gel under an electric field, proteins separate by molecular weight (size), with smaller proteins migrating faster.

What is the principle and application of the polymerase chain reaction (PCR)?

PCR amplifies specific DNA sequences through repeated cycles of denaturation, primer annealing, and extension by a thermostable DNA polymerase (Taq). Used for diagnosis, cloning, and genetic testing.

What does the Beer-Lambert law describe in spectrophotometry?

Absorbance is directly proportional to the concentration of the absorbing substance and the path length (A = epsilon * c * l), allowing quantification of solute concentration.

What is the principle of ELISA and a common application?

Enzyme-Linked Immunosorbent Assay uses antigen-antibody specificity with an enzyme-linked antibody producing a measurable color signal; used to detect/quantify proteins, hormones, and pathogens (e.g., HIV testing).