Fate of Pyruvate

Question 1

Where does pyruvate dehydrogenase occur

Answer 1

the mitochondrial matrix

Question 1

Under aerobic conditions, pyruvate is oxidized to ________ _______ by __________________ __________________

Answer 1

oxidized to acetyl CoA via pyruvate dehydrogenase

Question 2

How does pyruvate cross the mitochondrial membrane

Answer 2

via a transporter

Question 3

Why is pyruvate dehydrogenase important in metabolism

Answer 3

it is the linking pathway between glycolysis and the citric acid cycle

Question 4

What makes up the pyruvate dehydrogenase complex

Answer 4

pyruvate + CoASH = acetyl CoA + CO2
with 5 coenzymes: NAD+, FAD, TPP, pyrophosphate, and lipoate

Question 5

What are the 5 coenzymes used in the pyruvate dehydrogenase complex

Answer 5

NAD+
FAD
TTP
pyrophosphate
lipoate

Question 6

How is pyruvate converted to acetyl CoA (using CoASH as a cofactor)

Answer 6

ketone (of pyruvate) is oxidized to an acid (of acetyl CoA) which forms a thioester

Question 7

Why does NADH need to be transferred to the mitchondria following glycolysis

Answer 7

it needs to be reoxidized by the electron transport chain, which happens in the mitchondria, since glycolysis happens in the cytosol, NADH has to be moved into the mitochondria

Question 8

What shuttle systems are required to bring reducing equivalents (NADH and FADH2) across the mitochondrial membrane

Answer 8

malate-aspartate shuttle
OR
glycerol 3-phosphate shuttle

dependant on the tissue at hand

Question 9

What tissues is the malate-aspartate shuttle system specific to

Answer 9

liver, kidneys, heart

Question 10

What tissues is the glycerol 3-phosphate shuttle system specific to

Answer 10

skeletal muscle and brain

Question 11

How does the malate-aspartate shuttle work

Answer 11

oxaloacetate is converted to malate by oxidizing NADH+H to NAD+ so it can cross the membrane, then on the other side of the membrane malate is converted back to oxaloacetate by reducing NAD+ back to NADH+H to be sent to ETC
(then oxaloacetate is converted to aspartate to cross back over membrane, converted back to oxaloacetate to oxidize the next NADH+H molecule)

Question 12

How does the glycerol 3-phosphate shuttle work

Answer 12

dihydroxyacetone phosphate is converted to glycerol 3-phosphate via the oxidization of NADH+H to NAD+, and then glycerol 3-phosphate is converted back to dihydroxyactetone phosphate via reduction of FAD to FAH2 and the cycle continues

*reducing equivalents from NADH are passed onto FADH2 and delivered to coenzyme Q in the ETC

Question 13

Under anaerobic conditions, animals convert pyruvate to _______________

Answer 13

lactate

Question 14

When does pyruvate reduced to lactate always occur

Answer 14

in red blood cells (don’t have mitochondria therefore no oxygen)

Question 15

How is pyruvate converted to lactate

Answer 15

NADH works as a cofactor and is oxidized to NAD+ via the lactate dehydrogenase enzyme, causing pyruvate to gain 2 H+ and become lactate

Question 16

When does the Cori cycle occur

Answer 16

in recovery from strenuous exercise

Question 17

What occurs in the Cori cycle

Answer 17

some of the lactate produced in muscles is transported to the liver via the blood

Question 18

What does the liver do to lactate in the Cori cycle

Answer 18

gluconeogenesis - converts lactate back to glucose

Question 19

Where does the newly synthesized glucose in the Cori cycle go

Answer 19

back to the muscles to replenish muscle glycogen stores used in the exercise

Question 20

Yeast and other microorganisms convert pyruvate into __________________ under anaerobic conditions

Answer 20

ethanol

Question 21

What is the two step process of converting pyruvate to ethanol

Answer 21

1. pyruvate loses CO2 via pyruvate decarboxylase to become acetaldehyde
2. acetaldehyde is converted to ethanol via alcohol dehydrogenase (using NADH as a cofactor)

Question 22

What is important about using NADH as a cofactor to convert pyruvate to ethanol

Answer 22

NADH is oxidized to NAD+ so it can be recycled back up into glycolysis and continue anaerobically