Chapter 5, Problem 1R

Summary Introduction

To name:

The pathways diagrammed in parts (a), (b), and (c) of the given figure.

Introduction:

Cellular mechanisms involved in many reactions in which the transfer of electrons from one molecule to another take place by means of oxidation-reduction reactions. The oxidation and reduction reactions are always coupled, the form of undergoes oxidation and another form undergoes reduction simultaneously.

Explanation of Solution

1. The given diagram is the Calvin-Benson cycle. In this cycle, three molecules of carbon dioxide are fixed and one molecule of glyceraldehyde 3-phosphate is produced. After that, it leaves the cycle is shown in the below diagram.



2. The given b diagram resembles the Glycolysis pathway. In this pathway, the oxidation of glucose yields two molecules of pyruvic acid as its end product.



3. The below-given diagram is the Kreb’s cycle. Here, the decarboxylation of pyruvic acid produces one carbon dioxide molecule and one acetyl group.

Summary Introduction

To review:

The anabolic and catabolic mechanisms in the given pathways.

Introduction:

The cellular mechanism of all living organisms requires the energy for its metabolism. However, the conversion of energy from the organic compounds undergoes the catabolic and anabolic process in different pathways, such as glycolysis, TCA and Calvin-Benson cycle to produce the energy in the form of ATP.

Explanation of Solution

1. Glycolysis and the Citric acid cycle are the major pathways for anabolic and catabolic mechanisms of all organic molecules, such as carbohydrates, lipids, and proteins. Glycerol is catabolized as Dihydroxyacetone phosphate in the Glycolysis pathway (a) and fatty acids are catabolized as acetyl CoA int he TCA cycle (b).

2. Glutamic acid is catabolized in the Krebs cycle (c). Glutamic acid is an amino acid which is catabolized by Kreb’s cycle at α-ketoglutaric acid which is formed from isocitric acid.

3. In the Calvin-Benson cycle, Glyceraldehyde 3-phosphate is the end product, which enters into glycolysis. In glycolysis, the glucose is oxidized into pyruvate which is decarboxylated to acetyl group and entered into the Kreb’s cycle.

4. The Calvin cycle requires 18 molecules of ATP between glucose and glyceraldehyde 3- phosphate.

5. Three molecules of carbon dioxide (CO₂) is released in the Kreb’s cycle,

   • Between pyruvate to acetyl CoA.
   • Between isocitric acid to α-ketoglutarate (TCA cycle).
   • Between α-ketoglutarate to succinyl CoA.

6. The long chain hydrocarbon like such as acetyl group is catabolized in the TCA cycle at acetyl CoA. This acetyl group like hydrocarbons are catabolized by beta-oxidation which enters into the Kreb’s cycle.

7. The production of NADH, FADH2 or NADH in glycolysis, Calvin-Benson and TCA cycles are,

	Utilizes	Produces
Glycolysis		2 NADH
Calvin-Benson cycle	6 NADPH
Pyruvate to acetyl CoA		1 NADH
Isocitrate to α-ketoglutaric acid		1 NADH
α-keto-glutaric to succinyl CoA		1 NADH
Succinate to fumarate		1 FADH2
Malate to oxalate		1 NADH

8. The anabolic and catabolic pathways are integrated between,

   • In glycolysis, the anabolic and catabolic pathways integrated into dihydroxyacetone phosphate.
   • In the TCA cycle, the anabolic and catabolic pathways integrated into acetyl, oxaloacetic acid and ketoglutaric acid.