Chapter 19 (Citric Acid Cycle) Flashcards
Synthase
Uses a compound with a high energy bond to make another high energy bond
Citrate Synthase
Step 1
Condensation of Acetyl-CoA with Oxaloacetate to produce Citrate
Requires: H2O
Produces: CoA-SH
Irreversible
Citrate Synthase is a ___ enzyme and is inhibited by high concentrations of:
allosteric
NADH and Succinyl-CoA
The pro-S arm of Citrate is ___ and the pro-R arm is ___
Acetyl-CoA (top)
OAA (bottom)
We cannot oxidize a ___ alcohol
tertiary (found on the middle C of Citrate)
Aconitase
Step 2
The dehydration and rehydration of Citrate (moves -OH group) to produce Isocitrate
Reversible
Citrate is ___ because it has no stereocenters
Isocitrate is ___ and has ___ stereocenters
achiral
chiral
2
Why does only one stereoisomer form when making Isocitrate (out of a possible 4)
Because of the Fe-S cluster that helps orient the reaction (always happens on pro-R arm)
Isocitrate Dehydrogenase
Step 3
Isocitrate goes through oxidative decarboyxlation to become alpha-Ketoglutarate Requires: NAD+ First production of: NADH+H and CO2 (similar to 6-phosphogluconate DH) Irreversible
The CO2 eliminated during Isocitrate Dehydrogenase began the Citric Acid Cycle as ___ not ___
OAA
Acetyl-CoA
Isocitrate Dehydrogenase is a ___ enzyme and is inhibited by high concentrations of:
Is activated by high concentrations of:
allosteric
ATP and NADH
ADP and NAD+
A ___ does not need TPP (although a ___ does)
Beta-decarboxylation
Alpha-decarboxylation
Alpha-Ketoglutarate is the ___ to Glutamate
Keto acid
Alpha-Ketoglutarate Dehydrogenase
Step 4
Alpha-Ketoglutarate goes through oxidative decarboxylation to produce a Succinyl-CoA (which contains a high E thioester bond) Requires: NAD+ and CoA-SH Produces: NADH+H and CO2 Identical to PDH (same cofactors too) Irreversible
We can add ___ to a C=C to create a hydroxyl group
water
Succinyl CoA Synthetase
Step 5
The creation of Succinate through substrate level phosphorylation (proceeds through a phosphorylated His intermediate) Requires: GDP + Pi Produces: GTP + CoA-SH First energy yielding step Reversible
Synthetase
Same as a Synthase except it requires a nucleotide
Succinate is symmetrical so
we cannot tell the difference between arms when tracing radio labels (becomes 1/2)
Succinate Dehydrogenase
Step 6
Dehydration of Succinate into Fumarate (trans-form)
Requires: FAD
Produces: FADH2
Reversible
Succinate Dehydrogenase contains a ___ prosthetic group that is covalently bonded to a ___ residue which releases its gained electrons into the ___
FAD
His (always attached)
electron transport chain (FADH2)
When we go from C-C to C=C we need ___
FAD
All reactions of the Citric Acid Cycle occur in the ___, all the enzymes are ___ except for ___ because it is ___
mitochondrial matrix
water soluble proteins
Succinate Dehydrogenase
bound in the membrane
Fumarase
Step 7
Hydration of the double bond in Fumarate to form L-Malate
Requires: H2O
Reversible
Malate Dehydrogenase
Step 8
The oxidation of L-Malate to form Oxaloacetate
Highly endergonic reaction (+29.7 kJ/mol)
Requires: NAD+
Produces: NADH+H
Reversible
