Cellular Respiration and Enzymes

PS II of light reaction is involved in production of NADPH₂ from NADP. There is photolysis of water in PS II that releases hydrogen ion which goes to ionised NADP to form NADPH₂.

Photophosphorylation is the formation of ATP in the presence of sunlight in grana.

Fumarase is an example of lyases.

Zn²⁺ serves as a cofactor for carbonic anhydrase.

Correct answer. NAD⁺ is synthesised through two metabolic pathways. It is produced either in a de novo pathway from amino acids or in salvage pathway by recycling preformed components.

The enzyme histidine ammonia-lyase converts histidine into ammonia and urocanic acid. Adrenodoxin reductase is a mitochondrial flavoprotein. The enzyme functions as the first electron transfer protein of mitochondrial P450 systems. Aromatase, also called estrogen synthetase, is an enzyme responsible for a key step in the biosynthesis of estrogens. The enzyme urate oxidase (UO), catalyses the oxidation of uric acid to 5-hydroxyisourate. Hence, the correct sequence of codes is P - 2, Q - 4, R - 1, S - 3.

Regulation of fatty acids metabolism: Acyl-CoA movement into the mitochondrion is a crucial factor in regulation. Malonyl-CoA which is present in the cytoplasm in high amounts when metabolic fuels are abundant, inhibits carnitine acyltransferase, thereby preventing acyl-CoA from entering the mitochondrion. Furthermore, 3-hydroxyacyl-CoA dehydrogenase is inhibited by NADH and thiolase is inhibited by acetyl-CoA, so that fatty acids wil not be oxidized when there are plenty of energy-yielding substrates in the cell. Hence, only the statement Q is false.

Gluconeogenesis is the metabolic pathway of producing glucose from non-carbohydrate substrates like amino acids (from protein breakdown), lactate (from anaerobic glycolysis), and glycerol (from fat breakdown). Glycogenolysis is glycogen breakdown, glycogenesis is glycogen synthesis, so the correct answer is gluconeogenesis.

Otto H. Warnburg gave action of enzymes. The Nobel Prize in Physiology or Medicine 1931 was awarded to Otto Warnburg for his discovery of the nature and mode of action of the respiratory enzyme. The Nobel Prize in Chemistry 1958 was awarded to Frederick Sanger for his work on the structure of proteins, especially that of insulin.

Pyruvic acid from glycolysis enters the mitochondrial matrix and is converted to acetyl-CoA, which then enters the Krebs cycle (citric acid cycle). In this cycle, acetyl-CoA is completely oxidized to CO2 and H2O, generating NADH, FADH2, and GTP/ATP. The Calvin cycle fixes CO2 in photosynthesis, Hill reaction is part of photosynthesis, and nitrogen cycle is a biogeochemical cycle.

Adenosine triphosphate (ATP) is known as the energy currency of a cell.

This is the correct option.

The pyruvic acid transported into the mitochondrial matrix is not directly used in the Krebs cycle. First it loses a molecule of CO₂ as NAD⁺ is reduced to NADH. The remaining molecules, called acetyl group, attaches to coenzyme to form acetyl coenzyme A. The conversion of  pyruvic acid to acetyl CoA links glycolysis and the Krebs cycle. Pyruvic acid is the final product of glycolysis and acetyl CoA is the compound that enters the Krebs cycle.

Cytochrome c reductase (Complex III) is located on the outer membrane of mitochondria in the electron transport chain. Adenylate kinase and ATP synthetase are primarily associated with the inner membrane, while nucleoside diphosphokinase is mainly cytosolic.

Aerobic respiration is the oxidative breakdown of respiratory substrates (like glucose) with the help of oxygen, producing CO2, water, and ATP. Anaerobic respiration occurs without oxygen, fermentation is a type of anaerobic respiration in yeast/bacteria, and respiratory quotient is the ratio of CO2 produced to O2 consumed.