c430 TCA +PDH
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1. What is the central area of metabolism for all macronutrients?
2. What is the purpose of TCA cycle?
3. What are characteristics of a multienzyme complex? (2)
1. TCA cycle
2. Produce electron carriers to produce energy via oxidative phosphorylation in ETC
3. (1) at least one enzyme that is noncovalently associated w/ multienzyme complex and (2) catalyzes at least two sequential rxns
1. What must happen before glyc can continue into TCA?
2. What are advantages of a multienzyme complex? (3)
- 1. Increases collisions (having 5 seq rxns in same location increases changes of rxn)
- 2. Decreases side rxns (prevents charged organic molecules from floating off)
- 3. Allows for coordinate control (regulation)
- - One place on multi-enzyme unit turns all rxns off! efficient.
1. How many enzymes does PDH have? Name them.
2. How many cofactors needed? Name them. Which come from vitamins?
3. dG of rxn? What is the basic name for this rxn?
4. Write rxn
1. Multiple copies of 3 enzymes: PDH, dihydrolipoyl transacetylase, and dihydrolipoyl DH
2. TPP (B1), FAD(B2), NAD (B3), CoA (B5) and lipoate.
3. dG = -33.4 kJ/mol; oxidative decarboxylation.
What is this structure? Identify the separate parts.
What is the mechanism of PDH? (5)
1. How many rxns in TCA?
2. Describe first step (enzyme, substrate, product, dG)
3. Can you explain dG?
4. What is it inhibited by? (3) What else do these things inhibit?
- 1. 8
- 2. Citrate synthase: Acetyl CoA + OAA + H2O --> Citrate (6C) + CoA-SH
dG = -32.2 kJ/mol
3. CoA is high energy molecule, so this condensation rxn releases a lot of energy
Also true of DHs and enzymes with large free energy releases.
1. Describe the second rxn in TCA (how does cellular condition differ from standard conditions)
2. Describe third reaction in TCA. What happens? How is this rxn pulled to form its product? No dG
1. Aconitase (citrate --> isocitrate) - isomerase; dG = -13.3 kJ/mol, but in cell, its reversible.
2. Isocitrate dehydrogenase - isocitrate + NAD+ --> a-ketoglurate + CO2
Produces NADH; forms product b/c isocitrate is rapidly consumed in the next step. has Iron.
1. What is fourth enzyme of TCA? Describe rxn.
2. How is the energy from the rxn conserved?
3. What is this rxn similar to?
1. Oxidation of a-ketoglutarate to succinyl CoA + CO2: a-ketoglutarate DH complex
A-ketoglutarate + CoA-SH + NAD+ ---> succinyl CoA + NADH + CO2 (dG = -33.5 kJ/mol)
2. Energy from oxidation of a-ketoglutarate is conserved in the formation of the thioester bond in succinyl CoA
3. PDH - same structure, function, homologous enzymes, and uses same cofactors.
1. Describe 5th rxn of TCA
2. What should the free energy change be? What is the energy change? Why?
3. What is an important product? How is it formed?
1. Succinyl CoA Synthetase:
Succinyl CoA + GDP+Pi ---> Succinate + GTP + CoA-SH
2. Should be -36 kJ/mol, but it's -2.9 kJ/mol because the energy released is used to drive synthesis of phosphoanhydride bond in GTP/ATP
1. Describe 6th rxn.
2. What other role does the enzyme have?
3. What is dG?
4. What does it create? (short-term) and eventually?
1. Succinate DH: succinate + FAD--> Fumarate + FADH2
2. Complex II in ETC
3. dG = 0 freely revresible
4. FADH2 and eventually, each succinate will lead to 1.5 ATP molecules per pair of electrons.
1. Name all 8 enzymes of the TCA cycle
2. Why is hydrolysis of CoA so important at beginning?
2. B/c this makes the forward rxn highly xergonic. Large negative free energy change is needed b/c [OAA] is usually very low.
7th TCA rxn
1. Describe (dG)
2. What type of rxn is this?
3. What type of transition state does it have?
- 1. Fumarase: Fumarate + H2O --> Malate
- dG = -3.8 kJ/mol (reversible)
Last step of TCA (8)
2. What is dG? Why does it go forward?
L-malate + NAD+ --> OAA + NADH + H+
2. dG = + 29.7 kJ/mol because in cell, OAA is continually removed by highly exergonic citrate synthase, keeping [OAA] low, pushing rxn forward.
1. Name all 8 enzymes & accompanying reactions.
2. Note which steps produce NADH, FADH2, and GTP
3. Which steps release CO2? (2)
1. What activates PDH? Inhibits it? (4,4)
2. What activates Citrate synthase? Inhibits it?
3. What activates Isocitrate? Inhibits it? (2)
4. What activates a-ketoglutarate? (1) What inhibits it? (2)
1. AMP, CoA, NAD+, Ca2+; ATP, Acetyl CoA, NADH, fatty acids
2. ADP; citrate, ATP, succinyl CoA, NADH
3. Ca2+, ADP; ATP
4. Activated by Ca2+, inhibited by succinyl CoA, NADH.
Name all steps that create ATP and say how many ATP are (potentially) created
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