19. Pyruvate dehydrogenase

Question 1

what happens to pyruvate after glycolysis

Answer 1

sometimes it will build fatty acids or sterols, but often it moves forward towards cellular respiration

Question 2

what are the three major stages of pyruvate in cellular respiration

Answer 2

1. pyruvate oxidized into 2C acetyl CoA
2. acetyl CoA oxidized to CO2
3. reduced electron carriers transfer their electrons to O2 to produce H2O

Question 3

is pyruvate to acetyl CoA reversible or irreversible

Answer 3

irreversible

Question 4

what enzyme converts pyruvate to acetyl CoA

Answer 4

pyruvate dehydrogenase

Question 5

is pyruvate to acetyl CoA endergonic or exergonic

Answer 5

highly exergonic

Question 6

describe the type of reaction of pyruvate to acetyl CoA

Answer 6

oxidative decarboxylation and dehydrogenation

Question 7

other than the enzyme, what is requires to convert pyruvate to acetyl CoA

Answer 7

CoA-SH, NAD+, TPP, lipoate, FAD

Question 8

other than acetyl CoA, what is produced when pyruvate is converted to acetyl CoA

Answer 8

NADH and CO2

Question 9

what are the 5 coenzymes needed for pyruvate to acetyl CoA conversion

Answer 9

TPP, FAD, NAD+, lipoate, CoA

Question 10

which of the coenzymes from pyruvate to acetyl CoA are found in vitamins (and list the vitamins)

Answer 10

thiamine in TPP = B1
riboflavin in FAD = B2
niacin in NAD+ = B3
pantothenate in CoA = B5

Question 11

what is the role of lipoate

Answer 11

acts as a long arm, swinging between multiple enzyme sites

Question 12

describe the structure of lipoate

Answer 12

attached by an amide linkage to a lysine of E2

Question 13

what are two other names for lipoate

Answer 13

lipoyl group or lipollysine

Question 14

describe the structure of acetyl CoA

Answer 14

acetate is linked to CoA by an -SH group

Question 15

what type of molecule is acetyl CoA

Answer 15

thioester

Question 16

T or F: thioesters have a high acyl group transfer potential

Answer 16

true

Question 17

what does it mean for thioesters to have a high acyl group transfer potential

Answer 17

later, donation of acetate will release lots of free energy and be favorable

Question 18

describe the carbons/functional groups of pyruvate

Answer 18

3C, ketone and a carb acic

Question 19

describe the carbons/functional groups of acetate

Answer 19

2C, carb acid

Question 20

what are the 3 enzymes of pyruvate dehydrogenase complex

Answer 20

pyruvate dehydrogenase (E1), E2, E3

Question 21

how many consecutive reactions occur in the PDH complex

Answer 21

5

Question 22

describe step one of the PDH reactions

Answer 22

on E1, the C1 of pyruvate is released as CO2, and C2 is attached to the coenzyme TPP as a hydroxyethyl group

Question 23

describe step two of the PDH reactions

Answer 23

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

Question 24

describe step three of the PDH reactions

Answer 24

on E2, the acetate group is trans esterified from the -SH of lipoate to the -SH of CoA. Lipoyllysine is now fully reduced

Question 25

describe steps four and five of the PDH reactions

Answer 25

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+