01.29 - Lee - Citric Acid Cycle

01.29 - Lee - Citric Acid Cycle - Krebs Cycle Sir Hans...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Krebs Cycle Sir Hans Krebs 1900-1981 The Citric Acid Cycle Tricarboxylic Acid Cycle 1 2 Glucose NADH NADH FADH 2 O 2 H 2 O NAD + FAD ADP ATP Krebs Cycle 2CO 2 Pyruvate Acetyl CoA CO 2 GDP GTP Mitochondrion Energy Metabolism - mitochondrial oxidation Glucose to pyruvate - no oxygen involved. From pyruvate, one CO 2 is formed when it is converted to acetyl CoA. Acetyl CoA is oxidized to CO 2 by the Krebs Cycle. Here a large amount of the energy of oxidation is trapped by transfer of reducing equivalents (hydrogens) or electrons to NAD and FAD. Energy Metabolism 3
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Glucose Pyruvate In the KREBS CYCLE the two carbon fragment is cleaved and oxidized to CO 2 . CH 3 -C- C O CH 3 -C S-CoA O 2 CO 2 Krebs cycle Acetyl CoA CO 2 Stage 1: Pyruvate to Acetyl CoA. Pyruvate is decarboxylated and oxidized to an acetic acid thioester. Note: the carbons of glucose do not react with molecular oxygen but end up as CO 2 . OH O 4 Pyruvate + CoA + NAD + Acetyl CoA + CO 2 + NADH Pyruvate undergoes oxidative decarboxylation. PDH is localized in the mitochondria. Pyruvate dehydrogenase complex The Pyruvate Dehydrogenase Reaction 5 Pyruvate is readily decarboxylated to acetaldehyde and CO 2 . CH 3 -C-C O OH O CH 3 -C-H + CO 2 O CH 3 -C-S-CoA O CH 3 -C-OH O Oxidation Reaction 1. Reaction 2. The enzyme PDH carries out the basic two step chemical reaction at the right but the product is acetyl CoA. The Pyruvate Dehydrogenase Reaction: A Two Step Process - Decarboxylation and Oxidation. 6
Background image of page 2
Conversion of pyruvate to ethanol - fermentation. reminder Pyruvate is decarboxylated, and then reduced to ethanol; chemically we can think of the PDH reaction as one where pyruvate is decarboxylated and the aldehyde is then oxidized to acetic acid. CH 3 -C-H O CH 3 -C-OH O CH 3 -CH-OH O H Acetaldehyde H 2 0 -2H dehydrogenase Second reaction: acetaldehyde is oxidized - an acetaldehyde dehydrogenase. 7 8 •Pyruvate dehydrogenase is an example of a multi-enzyme complex. •There are three subunits, each with its own catalytic function. •These are called E1, E2 and E3. •The complex contains multiple copies of each. –In E. coli, the complex contains 24 E1, 24 E2 and 12 E3. The Pyruvate Dehydrogenase Enzyme Complex 9
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Mammalian PDH is similarly complex, but contains two additional regulatory enzymes, a kinase and a phosphatase. 10 Enzyme Bound Cofactors of PDH: Thiamine pyrophosphate (TPP) 11 Enzyme Bound Cofactors of PDH - Lipoamide and FAD: 12
Background image of page 4
Decarboxylation of pyruvate by the E1 enzyme •Pyruvate is bound to TPP on the E1 enzyme (pyruvate dehydrogenase) •E1 decarboxylates pyruvate - the hydroxyethyl-TPP can be looked upon as acetaldehyde that is bound to TPP. 13 •Next, the E1 enzyme transfers the hydroxyethyl-TPP to the lipoamide that is bound to the E2 enzyme. The disulfide of lipoamide is reduced in this process, while the hydroxethyl group is oxidized to an acetyl group (can be looked upon as oxidation of a bound aldehyde to acetic acid). By using these cofactors, pyruvate is decarboxylated and oxidized to an enzyme bound thioester of acetic acid.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 19

01.29 - Lee - Citric Acid Cycle - Krebs Cycle Sir Hans...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online