CHEM 440
Biochemistry I
J. D. Cronk   Syllabus [ Previous | Next ] Pick a lecture:
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Lecture 31. Citric acid cycle

Monday 29 November 2010

The fate of pyruvate, a key metabolic intermediate. Conversion of pyruvate to acetyl CoA by the pyruvate dehydrogenase complex {PDH complex}. A key coenzyme, thiamine pyrophosphate (TPP) cofactor: TPP chemistry, structure, and role in the PDH mechanism. PDH complex: Structure and function. Enzymes of the citric acid cycle: structure, function, and mechanism. Stoichiometry of the citric acid cycle. Regulation of acetyl CoA production by PDH and the citric acid cycle.

Reading: Voet, Voet, and Pratt; Ch.17, pp.566-587.
31. Summary

Lecture 31 Summary

Amphibolic nature of the citric acid cycle. Anaplerotic reactions and the example of pyruvate carboxylase. The glyoxylate cycle.

Intermediates of the citric acid cycle serve as precursors for various biosynthetic products. This "bleeding off" of intermediates is what makes the activity of pyruvate carboxylase essential. For example, succinyl CoA is the starting material for heme biosynthesis. The intermediates α-ketoglutarate and oxaloacetate can undergo transamination to form glutamate and aspartate, respectively.

Glyoxylate cycle

In plants and certain microorganisms, acetyl CoA can be reformed into succinate. The net synthesis of succinate from two molecules of acetyl CoA takes place in what is called the glyoxylate cycle. The cycle formally uses three enzymes from the citric acid cycle, citrate synthase, aconitase, and malate dehydrogenase. The enzymes isocitrate lyase [EC 4.1.3.1] and malate synthase [EC 2.3.3.9] are unique to the cycle.

 
 

Learning objectives

Page updated 07-20-10

References

  1. Howard BR, Endrizzi JA, Remington SJ. (2000) Crystal structure of Escherichia coli malate synthase G complexed with magnesium and glyoxylate at 2.0 A resolution: mechanistic implications. Biochemistry 39: 3156-3168.
 
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[ E-mail: cronk@gonzaga.edu ]