5. Nicotinamide Coenzymes as Reversible Redox Carriers The nicotinamide coenzyme

Question

5. Nicotinamide Coenzymes as Reversible Redox Carriers The nicotinamide coenzymes (see Fig. 13-24) can undergo reversible oxidation-reduction reactions with specific substrates in the presence of the appropriate dehydrogenase. In these reactions, NADH + H+ serves as the hydrogen source, as described in Problem 3. Whenever the coenzyme is oxidized, a substrate must be simultaneously reduced:

QUESTION: Which of the reactions detailed in question 5 (Chapter 16) requires NADH + H+ or H2O? EXPLAIN

Substrate NADH H+-product NAD Oxidized Re duced Re duced Oxidized For each of the reactions in (a) through (f) shown below, determine whether the substrate has been oxidized or reduced or is unchanged in oxidation state (see Problem 3). If a redox change has occurred, balance the reaction with the necessary amount of NAD+ ,NADH, H*, and H20 The objective is to recognize when a redox coenzyme is necessary in a metabolic reaction (a) CH3CH2OH CH3-C Ethanol Acetaldehyde (b) CH2 C-C CH - 1,3-Bisphosphoglycerate Glyceraldehyde 3-phosphate (c) CH3-C-C Pyruvate Acetaldehyde (d) CH3-C-C Pyruvate Acetate OH (e) OOC-CH2-C-CoO OOC CH2-C Coo Oxaloacetate Malate Acetoacetate Acetone

Explanation / Answer

Oxidation-reduction reactions carried out by dehydrogenases are specific for their substrates but often utilize common coenzymes or hydrogen carriers, eg, NAD+,

From a to f, we discuss whether the substrate is oxidised or reduced

a) Here oxidation of ethanol takes place which converts into carboxylic acid which requires NAH to reduced on the other hand.

b) Here, There is no change in oxidation state.

c) Reduction of a carboxylic group to aldehyde group takes place, so NADH is required to oxidised in the reaction.

e) Reduction of ketone group to alcohol group takes place, so NADH is required to oxidised in the reaction.

f) Reduction of a carboxylic group takes place, So NADH is required to oxidised in the reaction.

Related Questions

Navigate

• Browse (All)
• Browse 5
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.