GPAT Biochemistry Syllabus

How does a competitive inhibitor affect Km and Vmax?

It increases the apparent Km (lowers affinity) but Vmax remains unchanged, because the inhibitor competes at the active site and can be overcome by excess substrate.

How does a non-competitive inhibitor affect Km and Vmax?

It decreases Vmax but Km is unchanged, because it binds at a site other than the active site and is not overcome by increasing substrate.

What is the purpose of the Lineweaver-Burk plot?

It is a double-reciprocal plot (1/v vs 1/[S]) that linearizes the Michaelis-Menten equation; the y-intercept = 1/Vmax and the x-intercept = -1/Km.

What is the structure of DNA according to the Watson-Crick model?

A right-handed double helix of two antiparallel polynucleotide strands held by complementary base pairing (A-T, G-C), with a sugar-phosphate backbone.

State Chargaff's rules for DNA base composition.

In DNA, the amount of adenine equals thymine (A=T) and guanine equals cytosine (G=C); thus purines = pyrimidines.

How many hydrogen bonds form between A-T and between G-C base pairs?

Adenine-Thymine form 2 hydrogen bonds; Guanine-Cytosine form 3 hydrogen bonds (making GC-rich DNA more stable).

What is the function of DNA, and in which direction is it synthesized?

DNA stores and transmits genetic (hereditary) information; it is synthesized in the 5' to 3' direction by DNA polymerase.

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

mRNA (carries genetic code to ribosomes), tRNA (carries amino acids to the ribosome), and rRNA (structural/catalytic component of ribosomes).

How does RNA differ chemically from DNA?

RNA contains ribose sugar (vs deoxyribose), uracil instead of thymine, and is usually single-stranded; DNA is double-stranded with deoxyribose and thymine.

What is the anticodon, and on which RNA is it found?

A three-nucleotide sequence on tRNA that base-pairs with the complementary codon on mRNA during translation.

Name the four fat-soluble vitamins.

Vitamins A, D, E, and K.

What is the active form of vitamin A in vision, and what deficiency does it cause?

Retinal (11-cis-retinal forms rhodopsin); deficiency causes night blindness and xerophthalmia.

What is the main function of vitamin K, and its deficiency effect?

It is a cofactor for gamma-carboxylation of clotting factors (II, VII, IX, X); deficiency causes impaired blood clotting/bleeding.

What is the principal function of vitamin E?

It acts as a lipid-soluble antioxidant, protecting cell membranes and polyunsaturated fatty acids from free-radical oxidation.

List the water-soluble vitamins of the B-complex group and vitamin C.

B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), B12 (cobalamin), and vitamin C (ascorbic acid).

Which vitamin deficiency causes beriberi, and what coenzyme does it form?

Vitamin B1 (thiamine) deficiency causes beriberi; thiamine forms the coenzyme thiamine pyrophosphate (TPP).

What deficiency does vitamin C cause, and what is its key biochemical role?

Deficiency causes scurvy; vitamin C is required for hydroxylation of proline and lysine in collagen synthesis and acts as an antioxidant.

Which vitamin deficiency causes pernicious anemia and is linked to intrinsic factor?

Vitamin B12 (cobalamin); its absorption requires intrinsic factor secreted by gastric parietal cells.

What is a redox (oxidation-reduction) reaction?

A reaction involving the transfer of electrons; the species that loses electrons is oxidized (reducing agent) and the species that gains electrons is reduced (oxidizing agent).

What are the major electron carriers (coenzymes) in metabolic redox reactions?

NAD+/NADH, NADP+/NADPH, and FAD/FADH2 (and FMN); they shuttle electrons between metabolic reactions and the electron transport chain.

In oxidative phosphorylation, what is the final electron acceptor of the electron transport chain?

Molecular oxygen (O2), which is reduced to water at Complex IV (cytochrome c oxidase).

What is the general formula of monosaccharides and a common example?

(CH2O)n; e.g., glucose, fructose, and galactose are hexoses with the formula C6H12O6.

What distinguishes an aldose from a ketose monosaccharide?

An aldose has an aldehyde group (e.g., glucose); a ketose has a ketone group (e.g., fructose).

What is the difference between glucose and galactose / glucose and fructose as isomers?

Glucose and galactose are epimers (differ at C-4); glucose and fructose are functional-group isomers (aldose vs ketose), both being C6H12O6.

Name three important polysaccharides and their roles.

Starch (plant energy storage), glycogen (animal energy storage), and cellulose (plant structural component).

How do the glycosidic linkages in starch/glycogen differ from those in cellulose?

Starch and glycogen have alpha-1,4 (and alpha-1,6 branch) linkages digestible by humans; cellulose has beta-1,4 linkages that humans cannot digest.

What are the four levels of protein structure?

Primary (amino acid sequence), secondary (alpha-helix/beta-sheet from H-bonding), tertiary (3D folding of a polypeptide), and quaternary (assembly of multiple subunits).

What type of bond stabilizes the primary structure of a protein, and which stabilize tertiary structure?

Peptide (covalent) bonds stabilize primary structure; tertiary structure is stabilized by H-bonds, disulfide bridges, ionic bonds, and hydrophobic interactions.

What are the three stages of protein synthesis (translation)?

Initiation (ribosome assembles at start codon AUG), elongation (peptide chain grows codon by codon), and termination (release at a stop codon).

What is the start codon and which amino acid does it code for in eukaryotes?

AUG is the start codon; it codes for methionine.

What is sickle cell anemia and its molecular basis?

An inherited disorder caused by a single point mutation in the beta-globin gene (Glu to Val at position 6), producing HbS that polymerizes and distorts red cells into a sickle shape.

What is phenylketonuria (PKU) and which enzyme is deficient?

An inherited metabolic disorder caused by deficiency of phenylalanine hydroxylase, leading to accumulation of phenylalanine and intellectual disability if untreated.