LECTURE: Citric Acid Cycle - BIOCHEMICAL ENERGY PRODUCTION

Series of biochemical reactions in which the acetyl portion of acetyl CoA is oxidized to carbon dioxide and the reduce Coenzyme FADH2 and NADH

Citric Acid Cycle

discoverer of Citric Acid Cycle

Hans Adolf Krebs

Two important types of reactions

• Oxidation of NAD+ and FAD to produce NADH and FADH2

• Decarboxylation of citric acid to produce carbon dioxide

___ is made on the 5th reaction of citric acid cycle

GTP - Guanosine triphosphate

a starting material to produce acetyl CoA

Oxaloacetate

All of the chemical reaction of the citric acid cycle, takes place in the ______

mitochondrial matrix

• involved in catalyzing reaction that involves FAD

• located on the integral part of the inner mitochondrial membrane

• The only enzyme happens in the mitochondrial membrane

Succinate dehydrogenase

Reactions of the Citric Acid Cycle
What is Step 1?

Formation of Citrate

Reactions of the Citric Acid Cycle
What is Step 2?

Formation of Isocitrate

Reactions of the Citric Acid Cycle
What is Step 3?

Oxidation of Isocitrate and Formation of CO2: involves oxidation–reduction as well as decarboxylation

Reactions of the Citric Acid Cycle
What is Step 4?

Oxidation of Alpha-Ketoglutarate and Formation of CO2

Reactions of the Citric Acid Cycle
What is Step 5?

Thioester bond cleavage in Succinyl CoA and Phosphorylation of GDP

Reactions of the Citric Acid Cycle
What is Step 6?

Oxidation of Succinate

Reactions of the Citric Acid Cycle
What is Step 7?

Hydration of Fumarate

Reactions of the Citric Acid Cycle
What is Step 8?

Oxidation of L-Malate to Regenerate Oxaloacetate

2 important types of reaction:
Identify which reaction - produced FADH2 and NADH

Oxidation reaction

2 important types of reaction:
Identify which reaction - reaction wherein a carbon chain is shortened by a removal of carbon atom as carbon dioxide

Decarboxylation reaction

Enzyme used in Step 1: Formation of Citrate

citrate synthase

Two parts to the reaction in Step 1: Formation of Citrate

1. condensation of acetyl CoA and oxaloacetate to form citryl CoA

2. hydrolysis of the thioester bond in citryl CoA to produce CoA—SH and citrate

Enzyme used in Step 2: Formation of Isocitrate

aconitase

Step 2: Formation of Isocitrate
- Citrate is converted to cis form aconitate and cis aconitate will be converted into _____

Hint: Citrate is converted to its less symmetrical isomer

isocitrate

Enzyme used in Step 3: Oxidation of Isocitrate and Formation of CO2

isocitrate dehydrogenase

Reactants involved in Step 3: Oxidation of Isocitrate and Formation of CO2

NAD+ and isocitrate

Enzyme used in Step 4: Oxidation of Alpha-Ketoglutarate and Formation of CO2

a-ketoglutarate dehydrogenase complex

Reactants involved in Step 4: Oxidation of Alpha-Ketoglutarate and Formation of CO2

NAD, CoA—SH, and a-ketoglutarate

An aggregate of 3 enzyme called aketoglutarate dehydrogenase complex

Catalase

Products of Step 4: Oxidation of Alpha-Ketoglutarate and Formation of CO2

CO2, NADH, and the C4 species succinyl CoA

Enzyme used in Step 5: Thioester bond cleavage in Succinyl CoA and Phosphorylation of GDP

succinyl CoA synthetase

Reactants used in Step 5: Thioester bond cleavage in Succinyl CoA and Phosphorylation of GDP

Succinyl CoA, GDP, free phosphate group (Pi)

Product of Step 5: Thioester bond cleavage in Succinyl CoA and Phosphorylation of GDP

Succinate molecule

Enzyme used in Step 6: Oxidation of Succinate

succinate dehydrogenase

Reactants of Step 6: Oxidation of Succinate

Succinate and FAD

Product of Step 6: Oxidation of Succinate

Fumarate

only produces the trans isomer of this unsaturated diacid

Succinate dehydrogenase enzyme

Enzyme used in Step 7: Hydration of Fumarate

Fumarase

Reactants of Step 7: Hydration of Fumarate

Fumarate and H2O

Product of Step 7: Hydration of Fumarate

L-Malate

Enzyme used in Step 8: Oxidation of L-Malate to Regenerate Oxaloacetate

Malate dehydrogenase

Reactants of Step 8: Oxidation of L-Malate to Regenerate Oxaloacetate

L-Malate and NAD+

Product of Step 8: Oxidation of L-Malate to Regenerate Oxaloacetate

Oxaloacetate

When ATP supply is ____, ATP inhibits citrate synthase (Step 1 of Citric acid cycle)

High

When ATP levels are ___, ADP activates citrate synthase

Low

Similarly, ADP and NADH control isocitrate dehydrogenase:

• ____ acts as an inhibitor

NADH

Similarly, ADP and NADH control isocitrate dehydrogenase:

• ____ as an activator

ADP