7: The following statements (I - V) are either true or false characteristics and

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7: The following statements (I - V) are either true or false characteristics and functions of the important protein lactate dehydrogenase (LDH). L. 11· The two subunits LDH-H and LDH-M are encoded by the LDHA and LDHB genes. III. High levels of LDH in cerebrospinal fluid are often associated with bacterial IV. Mutations in the LDHA gene and resulting deficiencies in LDH-H activity can result V. LDH enzymes are most commonly specific for L-lactate and these L-LDH enzymes Plasma total LDH level is elevated in hemolysis respectively meningitis in Glycogen Storage Disease XI. have the EC number 1.1.1.27: D-LDH enzymes have the EC number 11.1.28 Which of the following options (A-»E) is/are CORRECT? (a) (b) (c) (d) (e) Statements I, III and V are true. Statements II, IV and V are false. Statements II and IV are false. All statements are false. All statements are true. 8: Arsenate is a toxic ion that can interfere with both glycolysis and oxidative phosphorylation. Arsenate resembles inorganic phosphate (P) and can replace it in many enzymatic reactions. One such reaction is catalysed by glyceraldehyde 3-phosphate dehydrogenase in glycolysis. Arsenate competes with phosphate for entry into the active site of glyceraldehyde 3-phosphate dehydrogenase and upon completion of the reaction, instead of the normal product, 1,3-bisphosphoglycerate, the mixed anhydride 1-arsenato- 3-phosphoglycerate is formed; this undergoes rapid spontaneous hydrolysis into arsenate plus 3-phosphoglycerate, the latter being a normal intermediate in glycolysis, so glycolysis is able to proceed from the step at 3-phosphoglycerate. What would be the effect of arsenate in glycolysis? (a) Arsenate activates glycolysis so that more ATP and NADH is generated for every glucose molecule. In the presence of arsenate there is no net formation of ATP from glycolysis, but NADH generation is not directly affected Arsenate brings glycolysis to an abrupt stop with immediate lethal consequences In the presence of arsenate glycolysis produces fewer ATP and NADH molecules per glucose molecule. Arsenate does not affect the number of ATP or NADH molecules generated per glucose molecule. (b) (c) (d) (e)

Explanation / Answer

7. During any type of tissue damage, as LDH is abundant in RBCs, hemolysis may cause the release of LDH into the plasma. So statement (I) is true.

The M and H subunits of LDH are encoded by two different genes found on two different chromosomes. The M subunit is encoded by LDHA and is located on chromosome 11 while, the H subunit is encoded by LDHB and is located on chromosome 12. So, statement (II) is incorrect.

High level of LDH in cerebrospinal fluid indicates a number of diseases involving the Central Nervous system. One of these diseases is Bacterial meningitis. Hence, option (III) is correct

Lactate dehydrogenase-A deficiency is caused by a mutation to the LDHA gene which causes a deficiency in the working of LDH-M subunit( not M subunit). This deficiency is also known as glycogen storage disease XI. Hence, Option IV is incorrect.

D- Ldh is recognized by an EC number of EC 1.1.2.4 and L-LDH is recognized by an EC number of 1.1.1.27. Hence, option (V) is incorrect.

So, from the above explanation, we can conclude that statements (II), (IV) and (V) are false. Option (b) is CORRECT.

8. From the given explanation it is clear that ATP production in Glycolysis is hampered during Arsenic poisoning since  ATP molecule that would be generated from 1,3-bisphosphoglycerate is not formed. Hence, the number of ATP and NADH molecules formed will be reduced.

So, Among the 4 statements given, Statement (d) "In the presence of arsenate, glycolysis produces fewer ATP and NADH molecules per glucose molecule." is correct.

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