Lecture 16 - Citric Acid Cycle 1 Flashcards
(13 cards)
Where is pyruvate from
Glycolysis generates pyruvate as its end product
Breakdown of some amino acids
The pyruvate has to be processed to remove it
Its fate depends upon the conditions
Under anaerobic conditions, what is pyruvate converted to
Lactate or
Ethanol
What is a PDHC
Pyruvate Dehydrogenase complex
multiple protein complex - 5 different coenzymes
What are the components in a PDHC
Pyruvate dehydrogenase (E1)
Dihydrolipoyl transferase (E2)
Dihydrolipoyl dehydrogenase (E3)
Other regulatory proteins
What are the PDHC coenzymes
Thiamine pyrophosphate (TTP)
Flavin adenine dinucleotide (FAD)
Nicotinamide adenine dinucleotide (NAD)
Coenzyme A (CoA)
Lipoate
What is the first step for the PDHC
The acetyl group is transferred to the TPP of the pyruvate dehydrogenase (E1)
Carbon dioxide is released
The acetyl group is not released
What is PDHC step 2
The acetyl group is esterified to the lipoate of dihydrolipoyl transacylase
The lipoate group is attached to E2 but the transfer is catalysed by E1
What is PDHC step 3
The acetyl group is transesterified to CoA (by E2)
and released as acetyl-CoA
What us PDHC step 4
The reduced lipoate is oxidized back to its starting form
The hydrogens are transferred to FAD, reducing it to FADH2 by dihydrolipoyl dehydrogenase (E3)
What is PDHC step 5
Electrons are transferred from FADH2 attached to the E3
to NAD+ forming NADH and H+
What is the PDHC mechanism
Intermediates are covalently bound – this means they cannot diffuse away
Lipoate is flexible – allows it to move to three different active sites
What does substrate channelling do
Allows several steps to proceed at a rate not limited by the free concentration of substrate
Prevents ‘side’ reactions
What does lipoate bind to
E2
