TCA cycle for exam 2

Question 1

How much ATP is generated in the PDH and the TCA cyclefrom one glucose molecule oxidized in glycolysis?

Answer 1

PDH produces 2 NADH and 2Acetyl CoA
2.5 ATP from 1 NADH, therefore 5 ATP from PDH

TCA produces 2 GTP and 6 NADH
therefore, 15 ATP + 2 GTP

Question 2

Which rxn generates ATP directly?

Answer 2

succinyl CoA synthestase (need nucleoside diphosphate kinase)

Question 3

Which rxn generate FADH2?

Answer 3

succinate DH

Question 4

Which rxns generate NADH?

Answer 4

malate DH
alpha ketoglutarate DH
isocitrate DH

Question 5

What are the two anaplerotic rxns?

Answer 5

pyruvate ____>oxaloacetate using pyruvate carboxylase

pyruvate _____> malate using malic enzyme

Question 6

What type of regulatory mechanisms does the PDH complex use to control activity?

Answer 6

allosteric (acetyl CoA, ATP, NADH are negative effectors) (NAD+ is a positive effector)
covalent (PDH kinase phosphorylates and inactivates)(PDH phosphatase dephosphorylates and activates)

Kinase is activated by CoA, ATP, and NADH

Question 7

What is a signal that ATP is low and the PDH phosphate should be activated?

Answer 7

Mg++

Question 8

What enzymes are regulated in the TCA cycle?

Answer 8

citrate synthase

isocitrate DH, alpha ketoglutarate DH

Question 9

How is citrate synthase regulated?

Answer 9

Substrate level control - [acetyl-CoA] and [oxaloacetate] vary with the metabolic state of the cell. This slight variation can change the activity of the enzyme.

Positive effectors - hi AMP/ADP concentrations means low energy (low levels of ATP)

negative effectors = NADH, ATP, succinyl CoA
If NADH and ATP concentrations are high, that indicates a high energy supply. FADH2 not so much bc it is bound and protected in an enzyme.

Succinyl CoA is an intermediate in the cycle. Comes after the last regulated step. If we start to see an accumulation of Succ CoA, it indicates the biosynthetic precursors are high. (Also regulates alpha KTG DH too)

Question 10

How is isocitrate DH regulated?

Answer 10

Allosteric
negative effectors = ATP and NADH, increasing concentrations indicate high energy supply
positive effector = AMP/ADP concentration increasing indicate ATP levels are low.

Question 11

How is alpha ketoglutarate DH regulated?

Answer 11

Allosteric
negative effectors - NADH and succ CoA
[NADH] increase indicates a hi energy supply
Such CoA is an intermediate in the cycle, but it is also the product of this rxn. [Succ CoA] increase indicates biosynthetic precursors are high. Comes after the last irreversible step of the TCA cycle.

positive effectors = AMP/ADP, increasing levels indicates ATP levels are low