Week 6-August 5

Week 6-August 5 - Week 6 August 5 2011 The Organic...

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Week 6 August 5, 2011 The Organic Chemistry of Life The famous poster “Biochemical Pathways” by G. Michal: (Go and see this poster in the basement of the Cabot Science Library, near the stairs.) Every biological process involves the breaking and forming of chemical bonds; these are chemical transformations (mostly organic chemistry). How is organic chemistry in the cell different from organic chemistry in the lab? Tonight, we’ll give you a tour of a few of these amazing transformations . . . 167
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Week 6 August 5, 2011 Bread and Beer Nearly all organisms get energy from glycolysis , the transformation of glucose into pyruvate: O HO HO HO OH OH glycolysis 2 glucose O O O pyruvate In yeast, pyruvate is converted into ethanol and CO 2 : O O O OH + CO 2 in yeast What use does the yeast have for ethanol and CO 2 ? What use do we have for ethanol and CO 2 ? How might the yeast accomplish this transformation? 168
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Week 6 August 5, 2011 Decarboxylation of Pyruvate with Thiamine The decarboxylation of pyruvate requires thiamine as a cofactor , in the form of a TPP ylide: SN Me R R' H TPP (Thiamine diphosphate) B: Me R R' TPP ylide Show how the TPP ylide can catalyze the decarboxylation of pyruvate. This reaction is the source of the CO 2 that makes bread rise and makes beer bubbly: O O O H + CO 2 O Me R R' pyruvate acetaldehyde Note how the TPP ylide turns a tough ! -decarboxylation into an easy " -decarboxylation. 169
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Week 6 August 5, 2011 Formation of Ethanol from Acetaldehyde with NADH The transformation of acetaldehyde into ethanol requires the cofactor NADH. Propose a mechanism: H O + N O H 2 N R H H N O H 2 N R + OH H NADH NAD + acetaldehyde ethanol What is the “orgo lab” equivalent of NADH? The reverse process, oxidation of ethanol to acetaldehyde, is catalyzed by an enzyme in your liver, liver alcohol dehydrogenase (LADH). This enzyme requires the cofactor NAD + . Why? What is the “orgo lab” equivalent of NAD + ? 170
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Week 6 August 5, 2011 Biosynthesis of Acetyl CoA Pyruvate is also the source of acetyl coenzyme A , a thioester that is the crucial building block for a huge number of biomolecules. The overall transformation involves the TPP ylide and a disulfide that is known as lipoamide . Let’s propose a mechanism: O O O SCoA O SN Me R R' HSCoA + pyruvate acetyl CoA S S R lipoamide + SH SH R dihydrolipoamide Why are thioesters like acetyl CoA so useful in biological systems?
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This note was uploaded on 07/28/2011 for the course CHEM S20 taught by Professor Evan during the Spring '11 term at Belhaven.

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Week 6-August 5 - Week 6 August 5 2011 The Organic...

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