19. Pyruvate dehydrogenase Flashcards
what happens to pyruvate after glycolysis
sometimes it will build fatty acids or sterols, but often it moves forward towards cellular respiration
what are the three major stages of pyruvate in cellular respiration
- pyruvate oxidized into 2C acetyl CoA
- acetyl CoA oxidized to CO2
- reduced electron carriers transfer their electrons to O2 to produce H2O
is pyruvate to acetyl CoA reversible or irreversible
irreversible
what enzyme converts pyruvate to acetyl CoA
pyruvate dehydrogenase
is pyruvate to acetyl CoA endergonic or exergonic
highly exergonic
describe the type of reaction of pyruvate to acetyl CoA
oxidative decarboxylation and dehydrogenation
other than the enzyme, what is requires to convert pyruvate to acetyl CoA
CoA-SH, NAD+, TPP, lipoate, FAD
other than acetyl CoA, what is produced when pyruvate is converted to acetyl CoA
NADH and CO2
what are the 5 coenzymes needed for pyruvate to acetyl CoA conversion
TPP, FAD, NAD+, lipoate, CoA
which of the coenzymes from pyruvate to acetyl CoA are found in vitamins (and list the vitamins)
thiamine in TPP = B1
riboflavin in FAD = B2
niacin in NAD+ = B3
pantothenate in CoA = B5
what is the role of lipoate
acts as a long arm, swinging between multiple enzyme sites
describe the structure of lipoate
attached by an amide linkage to a lysine of E2
what are two other names for lipoate
lipoyl group or lipollysine
describe the structure of acetyl CoA
acetate is linked to CoA by an -SH group
what type of molecule is acetyl CoA
thioester
T or F: thioesters have a high acyl group transfer potential
true
what does it mean for thioesters to have a high acyl group transfer potential
later, donation of acetate will release lots of free energy and be favorable
describe the carbons/functional groups of pyruvate
3C, ketone and a carb acic
describe the carbons/functional groups of acetate
2C, carb acid
what are the 3 enzymes of pyruvate dehydrogenase complex
pyruvate dehydrogenase (E1), E2, E3
how many consecutive reactions occur in the PDH complex
5
describe step one of the PDH reactions
on E1, the C1 of pyruvate is released as CO2, and C2 is attached to the coenzyme TPP as a hydroxyethyl group
describe step two of the PDH reactions
still on E1, the hydroxyethyl is oxidized to a carboxylic acid to form acetate. The two electrons removed from hydroxyethyl are used to reduce lipoate thiols from S-S to two -SH group. Acetate is esterified to one of the -SH groups of lipoyllysine, which is attached to E2
describe step three of the PDH reactions
on E2, the acetate group is trans esterified from the -SH of lipoate to the -SH of CoA. Lipoyllysine is now fully reduced
describe steps four and five of the PDH reactions
the oxidation of pyruvate drives the formation of the high energy acetyl CoA. Steps 4 and 5 now simply need to regenerate oxidized lipoate
step 4 on E3: electrons passed from lipoyllysine to FAD
step 5 on E3: electrons passed from FADH2 to NAD+
