Pyruvate Dehydrogenase and TCA: Theory Questions from Lecture Notes Flashcards
There are 2 ways that pyruvate can be metabolized: Explain them both briefly.
- Anaerobic conditions: pyruvate can be converted into either lactate or ethanol
- Aerobic conditions: pyruvate undergoes pyruvate dehydrogenase in order to be able to enter the TCA cycle
Pyruvate is converted to _______ which heads to the TCA cycle
Acetyl CoA
DNA —> mRNA
transcription
mRNA —> enzyme
translation
enzyme —> amino acid
turnover
mRNA —> nucleotides
turnover
Enzymes can undergo 4 different things: What are they?
- Association with regulatory protein
- Sequestration (compartmentation)
- Allosteric regulation
- Covalent modification
What 2 things does the fate of pyruvate depend on?
- presence/absence of O2
2. the type of organism
How does pyruvate get converted into lactate?
Through muscle
How does pyruvate get converted into ethanol?
Through yeast (production of ethanol releases CO2)
What enzyme converts pyruvate to lactate?
Lactate dehydrogenase
What are the cofactors when pyruvate is converted into lactate?
NADH + H+ —> NAD+
Describe the anaerobic metabolism of pyruvate in the muscle (lactate is being produced)
When available O2 is low, it is necessary to reoxidize NADH to NAD+ to keep glycolysis going.
The delta G is negative.
This occurs in skeletal muscle.
Lactate converted back to pyruvate in other tissues with high O2 (heart).
Describe Fermentation, the anaerobic metabolism of pyruvate in yeast (ethanol is being produced)
This has been exploited by the brewing industry to produce ethanol for beer, wine, or even to fuel cars
Yeast start using up the O2 in the medium but once it runs out they switch to fermentation
CO2 is released during process
NAD+ is produced to allow glycolysis to proceed
What enzyme converts pyruvate to acetaldehyde? (irreversible)
pyruvate decarboxylase
What are the cofactors when pyruvate is converted to acetaldehyde?
CO2 is lost
What enzyme converts acetaldehyde to ethanol? (reversible)
alcohol dehydrogenase
What are the cofactors when acetaldehyde is converted to ethanol?
NADH + H+ —-> NAD+
When alcohol is metabolized what is the toxic byproduct?
acetaldehyde (this is responsible for the hangover)
*Ethanol is metabolized in the liver that is why alcoholics have liver problems.
What is the process called when pyruvate is aerobically metabolized ?
Pyruvate dehydrogenase
What 3 major enzymes are a part of PDH?
E1: pyruvate decarboxylase (uses ATP)
E2: dihydrolipoate transacetylase (uses lipoic acid)
E3: dihydrolipoate dehydrogenase (NADH-FADH2 oxidoreductase)
Briefly explain the process of PDH
When oxygen levels are normal, oxidative phosphorylation can occur to produce NAD+ and pyruvate is metabolized more completely to produce NADH.
The NADH that is produced is then reoxidizes via the ETC (irreversible reaction).
Where does PDH occur in eukaryotes and bacteria?
Eukaryotes: mitochondria
Bacteria: cytosol
List some of the cofactors involved in PDH
FAD in E3 NAD Lipoic acid in E2 TPP in E1 CoA
What vitamins are required for PDH?
Riboflavin (B2) for FAD
Niacin (B3) for NAD
Pantothenate (B5) for CoA
Thiamine (B1) for TPP
Describe the PDH complex
-large complex
-12 subunits
-5X as big as one ribosome and can be seen with a microscope
When P is present, it is inactive
When P is not present, it is active
See slide 20
You can only enter TCA as ______
Acetyl CoA
You can only leave TCA as _______
CO2
