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
Under equilibrium conditions the concentration of Oxaloactetate will be (greater/less) than that of Malate, why?
less
because malate can leave the mitochondria and go on to gluconeogenesis
No Acetyl-CoA means a favor toward (Malate/OAA)
Malate
There is NO net production of ___
OAA
2 carbons in
2 carbons out
From glucose through glycolysis to the TCA cycle what is the net production of ATP
32 ATP
Although it does vary based on what shuttle is used
For this number NADH = 2.5xATP
FADH2 = 1.5xATP
