Lecture 16 - link reaction and citric acid cycle

Question 1

what could happen after pyruvate

Answer 1

aerobic = gets oxd to acetyl coA (link reaction)
anarobic = converted to ethanol
or lactate
depedning on cell type

Question 2

what enzyme converts pyruvate into acetyl coa

Answer 2

pyruvate dehydrogenase
(which converts NAD+ to NADH and also decarboxylates pyruvate)

Question 3

what bond is high energy bond in Acetyl coA

Answer 3

thioester bond between acetyl group and coA
-31kJ mol

Question 4

composition of pyruvate dehydrogenase complex

Answer 4

24x E1
24x E2
12x E3
60 total proteins make up the enzymje

Question 5

function of E1

Answer 5

pyruvate oxidative decarboxylation
so removes acetyl group

Question 6

function of E2

Answer 6

transferring acetyl group to coA

Question 7

function of E3

Answer 7

cofactor regeneration

Question 8

why does pyruvate need to pass into the mitochondria

Answer 8

pyruvate dehydrogenase is in the mt

Question 9

how does pyruvate pass into mt

Answer 9

can cross outer memb easy
inner memb needs to pass through pyruvate translocase (a pyruvate/H+ symporter)

Question 10

“first” step of citric acid cycle

Answer 10

oxaloacetate (4C) added to acetyl coA (2C)
to make citrate (6C)
and CoA comes off in a condensation reaction

Question 11

what stage is the first NADH and CO2 formed and how

Answer 11

isocitrate turns to alpha-ketoglutamate
via isocitrate dehydrogenase

Question 12

what stage is the first NADH and CO2 formed and how

Answer 12

isocitrate turns to alpha-ketoglutamate
via isocitrate dehydrogenase

Question 13

when is 2nd NADH and CO2 formed

Answer 13

alpha ketoglutarate turns to succinyl-coA
via the corresponding dehydrogenase
(remember, coA added at this stage)

Question 14

at what stage does substrate level phosph occur

Answer 14

succinyl-CoA turns to succinate
via succinyl-coa synthetase
and GDP/ADP turns to GTP/ATP
and coA comes off

Question 15

what stage is FADH2 made

Answer 15

succinate to fumarate
via succinate dehydrogenase

Question 16

when is the final NADH formed

Answer 16

after fumarate hydrated to malate
malate turns back into oxaloacetate via malate dehydrogenase

Question 17

total NADH, FADH2, GTP/ATP and CO2 formed after citric acid cycle (per cycle not per glucose)

Answer 17

3 NADH
2 CO2
1 FADH2
1 ATP/GTP

Question 18

how many ATP formed from each NADH and FADH2

Answer 18

n = 2.5
f = 1.5

Question 19

total amount of ATP made from whole process from 1 glucose

Answer 19

30-32

Question 20

why is it 3 or 5 ATP made

Answer 20

the nadh from glycolysis has to pass thorugh either the
- malate-aspartate shuttle (makes 2.5)
or
- glycerol phosphate shuttle (in brown adipose tissue, makes 1.5)

Question 21

what allows NADH to be oxd in malate aspartate shuttle

Answer 21

oxaloacetate
oxides NADH and in turn gets turned into malate
malate passes through into the mito matrix and reduces another NAD+ into NADH
so overall 1 NADH passes into matrik

Question 22

what 2 things cause feedback inhibition of pyruvate dehydrogenase

Answer 22

acetyl coA inhibits E2
NADH inhibits E3

Question 23

what will allow feed forward activation of pyruvate dehydrogenase

Answer 23

lots of NAD+

Question 24

what would cause the rate of the citric acid cycle decrease

Answer 24

lots of ATP