6. Carbohydrate 4 Flashcards
What happens to pyruvate before it enters the TCA cycle?
• it is transported from the cytoplasm to the mitochondrial matrix across the mitochondrial membrane
• the pyruvate combines with coenzyme A to form acetyl coenzyme A in the presence of pyruvate dehydrogenase
(CH3COCOOH + CoA + NAD+ —-> CH3CO~CoA + CO2 + NADH + H+)
What is the function of a coenzyme
Helps enzymes perform their function - coenzyme A carry two atoms in an activated form
How do we know a reaction is unidirectional?
When CO2 is released
Is the convention f pyruvate to acetyl CoA reversible is irreversible?
Irreversible so is a key regulator
Describe the structure of pyruvate dehydrogenase?
PDH is a large multi-enzyme complex (5 enzymes)
What does pyruvate dehydrogenase require?
The different enzyme activities require various cofactors (FAD,
thiamine pyrophosphate and lipoic acid). B-vitamins provide
these factors, so reaction is sensitive to Vitamin B1 deficiency.
What is pyruvate dehydrogenase activated by?
- pyruvate
- CoASH
- NAD
- ADP
- insulin
- dephosphorylation
What is pyruvate dehydrogenase inhibited by?
acetyl-CoA
NADH
ATP
citrate
phosphorylation
describe an overview of the Tricarboxylic Acid (TCA) cycle
• Mitochondrial • A single pathway – • Acetyl (CH3CO-) converted to 2CO2 • Oxidative (requires NAD+, FAD) • Some energy produced (as ATP/GTP) • (Also produces precursors for biosynthesis)
describe the steps in the Tricarboxylic Acid (TCA) cycle
- acetyl CoA(2C) combines with oxaloacetate(4C) to form citrate (6C).
- the citrate (6C) is converted to another 6C molecule.
- it is then converted to isocitrate(6C) which is converted to a 5C molecule by releasing CO2 and reducing NAD to NADH
- the 5C is converted to a 4C molecule by addition of CoA and release of CO2 and reduction of NAD to NADH
- the 4C is converted to another 4C molecule by converting GDP to GTP(substrate level phosphorylation) and release of CoA.
- the 4C is converted to another 4C by reduction of FAD to FADH2
- the 4C is converted to another 4C by addition of H2O
the 4C is converted to another 4C by reduction of NAD to NADH. this 4C then can combine with another acetyl CoA
what are the products of the TCA cycle for each glucose molecule?
6 NADH
2 FADH2
2 GTP
can the TCA cycle be regulated?
yes, there are two steps that are irreversible.
which 2 steps are regulated?
- the conversion of the 6C molecule to 5C molecule by release of CO2 and reduction of NAD to NADH
- the conversion of the 5C molecule to 4C molecule by release of CO2 and reduction of NAD to NADH
which enzyme is involved in the conversion of the 6C to 5C?
Isocitrate dehydrogenase
which enzyme is involved in the conversion of the 5C to 4C?
a-ketoglutarate dehydrogenase
what stimulates Isocitrate dehydrogenase
ADP
what inhibits Isocitrate dehydrogenase
NADH, ATP
what inhibits a-ketoglutarate dehydrogenase?
NADH, ATP, succinyl-CoA