Johnson - Metabolism (Link and Krebs) Flashcards
what is the first step in link and which enzyme catalyses it?
Pyruvate +TPP —> hydroxyethyl-TPP + CO2
catalysed by pyruvate decarboxylase
what is the second step in link and which enzyme catalyses it?
Hydroxyethyl-TPP and lipoamide form acetyl-dihydrolipoamide. This reacts with CoA forming acetyl CoA and a reducing lipoamide. This is catalysed by dihydrolipoyl transacetylase
what is the third step in link and which enzyme catalyses it?
The reducing lipoamide is oxidised (donates 2H+ and 2e-) by FAD (bound to enzyme dihydrolipoyl dehydrogenase) forming FADH2. FADH2 is oxidised by NAD+ forming NADH + H+ (NAD+ holds 2e- and 1H+)
what is the first step in krebs and which enzyme catalyses it?
Acetyl-CoA + H2O + oxaloacetate —> citrate + CoA
(2H from acetyl-CoA and 2H from H2O to make citrate)
catalysed by citrate synthase
what is the second step in krebs and which enzyme catalyses it?
citrate —> isocitrate
aconitase (aconitate intermediate)
what is the third step in krebs and which enzyme catalyses it?
isocitrate —> alpha-ketoglutarate + CO2
(uses NAD+)
isocitrate dehydrogenase
what is the fourth step in krebs and which enzyme catalyses it?
alpha-ketoglutarate + CoA —> CO2 + succinyl-CoA
(uses NAD+)
alpha-ketoglutarate dehydrogenase
what is the fifth step in krebs and which enzyme catalyses it?
succinyl-CoA + H2O + ADP + Pi —> ATP + succinate + CoA
succinyl-coA synthetase
what is the sixth step in krebs and which enzyme (and cofactor) catalyses it?
Succinate ---> fumarate succinate dehydrogenase (uses FAD)
what is the seventh step in krebs and which enzyme catalyses it?
fumarate + H2O —> Malate
fumarase
what is the eighth step in krebs and which enzyme catalyses it?
malate ---> oxaloacetate malate dehydrogenase (uses NAD+)
describe the structure of the pyruvate dehydrogenase complex
made of 3 enzymes; pyruvate decarboxylase (PD), dihydrolipoyl transacetylase & dihydrolipoyl dehydrogenase. approximately 60 polypeptide chains
what is the key linkage in acetyl-CoA?
thioester linkage, the hydrolysis of which is energetically favourable.
which part of acetyl-CoA is oxidised in krebs?
acetyl fragment
how does the pyruvate dehydrogenase complex increase efficiency?
uses substrate channeling instead of products diffusing to next active site they are passed (increases reaction rate and efficiency as well as decreasing unwanted side reactions) the lipoamide cofactor ‘fishes’ for hydroxyethyl substrate (carries it from e1 to e2 to e3)
are fats more or less reduced than sugars? what is the significance of this upon oxidation?
fats are more reduced than sugars therefore they generate more energy when oxidised
what does a lipase do?
breaks down fats into glycerol and 3 f/a’s
how does glycerol enter glycolysis?
glycerol —> DHAP
how do fatty acids enter glycolysis?
f/a beta-oxidation
f/a’s activated by linkage to Acetyl-CoA (requires ATP –> AMP + Pi) and then transported into mitochondria. 4 enzymes then oxidise the f/a-CoA one carbon unit at a time. The -ve deltaG reactions are coupled to NADH and FADH2 formation
describe the types of functional groups and linkage that must be present in order for C-C cleavage to occur
C-C cleavage between:
adjacent carbons, with a carbonyl next to one of the carbons
an alpha-hydroxyketone (hydroxyl on alpha C)
