Answer to Question #177230 in Biochemistry for Kim

Question #177230

1. Which of the following processes generates the most ATP? (Account for the no. of ATP)

a.) Citric Acid Cycle

b.) Fatty Acid oxidation

c.) Glycogenolysis

d.) Glycolysis

e.) Pentose phosphate pathway

Expert's answer

1-KREBS CYCLE: - The Krebs cycle only produces 2 molecules of ATP from every pyruvate molecule during the conversion of succinyl-CoA to succinate in the presence of enzyme Succinyl CoA synthetase

2 acetyl groups + 6 NAD+ + 2 FAD + 2 ADP + 2 Pi

   yields 4 CO2 + 6 NADH + 6 H+ + 2 FADH2 + 2 ATP


2-fatty acid oxidation: -During fatty acid β-oxidation long chain acyl-CoA molecules – the main components of FAs – are broken to acetyl-CoA molecules.

Fatty acid transport into mitochondria then beta oxidation takes place Beta-oxidation consists of four steps:

1) Dehydrogenation catalyzed by acyl-CoA dehydrogenase, which removes two hydrogens between carbons 2 and 3.

2) Hydration catalyzed by enoyl-CoA hydratase, which adds water across the double bond.

3) Dehydrogenation catalyzed by 3-hydroxyacyl-CoA dehydrogenase, which generates NADH.

4) Thiolytic cleavage catalyzed beta-ketothiolase, which cleaves the terminal acetyl-CoA group and forms a new acyl-CoA which is two carbons shorter than the previous one.

The shortened acyl-CoA then reenters the beta-oxidation pathway

ATP SYNTHESIS: -Acetyl-CoA generated by the beta-oxidation pathway enters the mitochondrial TCA cycle, where is further oxidized to generate NADH and FADH2. The NADH and FADH2 produced by both beta oxidation and the TCA cycle are used by the mitochondrial electron transport chain to produce ATP. Complete oxidation of one palmitate molecule (fatty acid containing 16 carbons) generates 129 ATP molecules.


3-GLYCOGENOLYSIS: -Glycogenolysis is the biochemical pathway in which glycogen breaks down into glucose-1-phosphate and glycogen. The reaction takes place in the hepatocytes and the myocytes. The process is under the regulation of two key enzymes: phosphorylase kinase and glycogen phosphorylase. Glycogenolysis, which is first initiated by the breakdown of glycogen to free glucose-1-phosphate (G-1-P), eventually generates a net total of 31–33 ATP molecules from G-1-P depending on the electron shuttle system used by the cell.


4-GLYCOLYSIS: -Glycolysis occurs in both aerobic and anaerobic states. In aerobic conditions, pyruvate enters the citric acid cycle and undergoes oxidative phosphorylation leading to the net production of 32 ATP molecules. In anaerobic conditions, pyruvate converts to lactate through anaerobic glycolysis. Anaerobic respiration results in the production of 2 ATP molecules

Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, and produce 2 ATP.

5-PENTOSE PHOSPHATE PATHWAY: -The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides.[2] While the pentose phosphate pathway does involve oxiin pentose phosphate pathway dation of glucose, its primary role is anabolic rather than catabolic. 

Only 1ATP is produced in Pentose phosphate pathway.

a.) Citric Acid Cycle            = 2 ATP

b.) Fatty Acid oxidation    = 129 ATP

c.) Glycogenolysis              =  33 ATP

d.) Glycolysis                      = 2 ATP

e.) Pentose phosphate pathway     = 1 ATP


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