Question

Identify the oxidized and reduced forms from the following pairs:

Answer 1

Answer:

1. NAD⁺ is the oxidized form and NADH  is the reduced form

2. Pyruvate is the oxidized form and Lactate is the reduced form.

3. Oxaloacetate is the oxidized form and Malate is the reduced form.

4. Fumarate is the oxidized form and Succinate is the reduced form.

5. FMN is the oxidized form and FMNH₂  is the reduced form

6. α-ketoglutarate is the oxidized form and Isocitrate is the reduced form.

7. O₂ is the oxidized form and  H₂O₂ is the reduced form.

Explanation:

Oxidation is the gain of oxygen or loss of electrons or hydrogen. Whereas, reduction is the loss of oxygen or gain of electrons or hydrogen.

1. NAD⁺/NADH

NAD⁺ is the oxidized form and NADH  is the reduced form of Nicotinamide adenine dinucleotide, NAD.

Therefore, NAD⁺ gets reduced to NADH by accepting electrons and proton.

NAD⁺ + 2 e⁻ + H⁺ → NADH

2. Pyruvate/lactate

Pyruvate, CH₃COCOO⁻, is the conjugate base of Pyruvic acid.

Lactate, CH ₃CH(OH)COO⁻, is the conjugate base of Lactic acid.

Reduction of Pyruvate to lactate:

CH₃COCOO⁻ + NADH  ⇌ CH ₃CH(OH)COO⁻ + NAD⁺

This reaction is catalyzed by the enzyme lactate dehydrogenase.

Therefore, Pyruvate is the oxidized form and Lactate is the reduced form.

3. Malate/oxaloacetate

Oxaloacetate, ⁻O₂CC(O)CH₂CO₂⁻, is the conjugate base of oxaloacetic acid.

Malate,⁻O₂CCH(OH)CH₂CO₂⁻, is the conjugate base of Malic acid.

Oxidation of Malate to Oxaloacetate:

⁻O₂CCH(OH)CH₂CO₂⁻ + NAD⁺  ⇌ ⁻O₂CC(O)CH₂CO₂⁻ + NADH

This reaction is catalyzed by the enzyme malate dehydrogenase.

Therefore, Oxaloacetate is the oxidized form and Malate is the reduced form.

4. Fumarate/succinate

Fumarate, ⁻O₂CCH=CHCO₂⁻, is the conjugate base of Fumaric acid.

Succinate, ⁻O₂CCH₂CH₂CO₂⁻, is the conjugate base of Succinic acid.

Oxidation of succinate to fumarate:

⁻O₂CCH₂CH₂CO₂⁻ + FAD ⇌ ⁻O₂CCH=CHCO₂⁻ + FADH₂

This reaction is catalyzed by the enzyme succinate dehydrogenase.

Therefore, fumarate is the oxidized form and succinate is the reduced form.

5. FMN/FMNH₂

FMN is the oxidized form and FMNH₂  is the reduced form of riboflavin-5′-phosphate or Flavin mononucleotide.

Therefore, FMN gets reduced to FMNH₂  by accepting electrons and proton.

FMN + 2 e⁻ + 2H⁺ → FMNH₂

     

6. α-ketoglutarate/isocitrate

α-ketoglutarate, ⁻O₂CC(O)CH₂CH₂CO₂⁻, is the conjugate base of α-Ketoglutaric acid.

Isocitrate, ⁻O₂CCH(OH)CH(CO₂⁻)CH₂CO₂⁻, is the conjugate base Isocitric acid.

Oxidation of Isocitrate to α-ketoglutarate:

⁻O₂CCH(OH)CH(CO₂⁻)CH₂CO₂⁻ + NAD⁺ → ⁻O₂CC(O)CH₂CH₂CO₂⁻ + CO₂ + NADH

This reaction is catalyzed by the enzyme Isocitrate dehydrogenase.

Therefore, α-ketoglutarate is the oxidized form and Isocitrate is the reduced form.

7. H₂O₂/O₂

Hydrogen peroxide, H₂O₂, is synthesized from hydrogen (H₂) and oxygen (O₂) in the presence of a catalyst.

H₂ + O₂ → H₂O₂

Oxygen gets reduced from 0 oxidation state in O₂ to -1 oxidation state in H₂O₂.

Therefore, O₂ is the oxidized form and  H₂O₂ is the reduced form.