Unit 6 - TCA

Question 1

what percentage of ATP is produced under aerobic conditions?

Answer 1

over 90% of ATP

-due to TCA and oxidative phosphorylation in mitochondria

Question 2

where are mitochondria most plentiful and where are they not?

Answer 2

most plentiful in cells with high E needs
-heart (contraction)
-kidney (transport)
-liver (biosynthesis)
not in mature erythrocytes

Question 3

how much do mitochondria count for in liver cells?

Answer 3

up to 20% of total PRO

Question 4

where does TCA happen compared to oxidative phosphorylation?

Answer 4

TCA: matrix
OP: embedded in inner membrane facing matrix

Question 5

how is heavy traffic between cytoplasm and matrix space of mitochondria controlled?

Answer 5

controlled by specific transport systems except for O2 and CO2, which diffuse thru membrane

• pyruvate enters from cytoplasm to matrix
• cotransport for “X” (from matrix to cytoplasm) and “X”H2 (from cytoplasm to matrix)
• -from NAD+ –> NADH RXN
• ATP/ADP cotransport (ATP from matrix to cytoplasm)
• Pi from cytoplasm to matrix

Question 6

is there a transport system for NADH in the matrix?

Answer 6

no
-reducing equivalents from glycolytic NADH are transferred by indirect processes to matrix space or respiratory-chain component that faces intermembrane space

Question 7

what are the 3 main functions of the TCA?

Answer 7

1. convert number of different fuels to a common mobile fuel (NADH)
2. serve as final meeting place for nearly all oxidizable substrates
3. provide intermediates for biosynthesis

Question 8

how does the mechanism of succinyl-CoA synthetase illustrate the common intermediate principle?

Answer 8

S~CoA + Pi + E E-S~P + CoA
E-S~P E~P + succinate
E~P + GDP E + GTP
(where ~ means E-rich)

E~P is phosphohistidyl to couple exergonic RXN to endergonic RxN

Question 9

what is the pyruvate dehydrogenase complex comprised of and located?

Answer 9

in the mitochondrial matrix space to oxidize pyruvate to ACoA (connecting link between glycolysis and CAC)

1. pyruvate dehydrogenase (E1)
2. dihydrolipyl transacetylase (E2)
3. dihydrolipyl dehydrogenase (E3)

Question 10

what is the importance of lipoamine’s structure?

Answer 10

it’s a swinging arm, meaning kinetics are fast

-E2 can create multiple lipoamides

Question 11

what is the main site of action for arsenite poisoning?

Answer 11

dihydrolipoamine

Question 12

why does the citrate synthetase reaction occur, even though it gives off energy?
(remember: ACoA + OAA –> citryl CoA + H2O –> citrate + CoA giving off 7.5 kcal/mol)

Answer 12

this E is used to help malate dehydrogenase (malate + NAD+ –> NADH + H + OAA)

• since very little OAA is in equilibirum with large amount of malate, it uses up E to happen (7.1 kcal/mol)
• but more malate can be a good thing in resting state, because malate can exit the cytoplasm to serve as substrate for gluconeogenesis