The malate-aspartate shuttle which transport NADH operates in... | Agrigyan

• Irreversible Regulatory Steps in Glycolysis: Glycolysis consists of three physiologically irreversible, exergonic steps:

• Hexokinase / Glucokinase: $\text{Glucose} + \text{ATP} \to \text{G6P} + \text{ADP}$
• Phosphofructokinase-1 (PFK-1): $\text{Fructose 6-phosphate} + \text{ATP} \to \text{Fructose 1,6-bisphosphate} + \text{ADP}$ (Statement B)
• Pyruvate Kinase: $\text{Phosphoenolpyruvate} + \text{ADP} \to \text{Pyruvate} + \text{ATP}$ (Statement C)
  • Reversible Steps:

• Phosphoglucose isomerase converts glucose-6-phosphate to fructose-6-phosphate in a freely reversible reaction.
• Lactate dehydrogenase catalyses the freely reversible interconversion of pyruvate and lactate.
• Conclusion: Reactions (B) and (C) only are irreversible steps of glycolysis.

• Endoplasmic Reticulum and Intracellular Targeting Signals:
• KDEL (Lys-Asp-Glu-Leu): The canonical C-terminal retention/retrieval signal that directs soluble resident proteins back to the endoplasmic reticulum lumen from the cis-Golgi.
• SKL (Ser-Lys-Leu): C-terminal peroxisome targeting signal 1 (PTS1).
• Pro-Lys-Lys-Lys-Arg-Lys-Val: Classical monopartite nuclear localization signal (NLS).
• Exam Context: The official answer key designated option (3) representing all recognized peptide targeting motifs governing intracellular polypeptide sorting.

Correct option: (3) (A), (B), (C) and (D).

• Vitamin $\text{B}_{12}$ (Cobalamin) Dependent Enzymes: In mammalian cells, only two enzymes require cobalamin coenzymes:

• Methylmalonyl-CoA mutase: Requires adenosylcobalamin (5'-deoxyadenosylcobalamin) to convert L-methylmalonyl-CoA to succinyl-CoA in propionate and odd-chain fatty acid metabolism.
• Methionine synthase (homocysteine methyltransferase): Requires methylcobalamin to transfer a methyl group from $N^5$-methyltetrahydrofolate to homocysteine, forming methionine and regenerating tetrahydrofolate (THF).
  • Other Enzymes:

• Pyruvate dehydrogenase: Requires TPP (Vitamin $\text{B}_1$), Lipoic acid, FAD (Vitamin $\text{B}_2$), $\text{NAD}^+$ (Vitamin $\text{B}_3$), and CoA (Vitamin $\text{B}_5$).
• Catalase: Heme metalloenzyme (iron-dependent).
• Conclusion: Therefore, (A) and (C) only are vitamin $\text{B}_{12}$-dependent enzymes.

Evaluating the Assertion and Reason concerning Estimation and analysis of carbohydrates and lipids:

The correct answer is Option 4: (A) is not correct but (R) is correct..