Chapter 19 (Citric Acid Cycle)

Question 1

Synthase

Answer 1

Uses a compound with a high energy bond to make another high energy bond

Question 2

Citrate Synthase

Step 1

Answer 2

Condensation of Acetyl-CoA with Oxaloacetate to produce Citrate
Requires: H2O
Produces: CoA-SH
Irreversible

Question 3

Citrate Synthase is a ___ enzyme and is inhibited by high concentrations of:

Answer 3

allosteric

NADH and Succinyl-CoA

Question 4

The pro-S arm of Citrate is ___ and the pro-R arm is ___

Answer 4

Acetyl-CoA (top)

OAA (bottom)

Question 5

We cannot oxidize a ___ alcohol

Answer 5

tertiary (found on the middle C of Citrate)

Question 6

Aconitase

Step 2

Answer 6

The dehydration and rehydration of Citrate (moves -OH group) to produce Isocitrate
Reversible

Question 7

Citrate is ___ because it has no stereocenters

Isocitrate is ___ and has ___ stereocenters

Answer 7

achiral
chiral
2

Question 8

Why does only one stereoisomer form when making Isocitrate (out of a possible 4)

Answer 8

Because of the Fe-S cluster that helps orient the reaction (always happens on pro-R arm)

Question 9

Isocitrate Dehydrogenase

Step 3

Answer 9

Isocitrate goes through oxidative decarboyxlation to become alpha-Ketoglutarate
Requires: NAD+
First production of: NADH+H and CO2
(similar to 6-phosphogluconate DH)
Irreversible

Question 10

The CO2 eliminated during Isocitrate Dehydrogenase began the Citric Acid Cycle as ___ not ___

Answer 10

OAA

Acetyl-CoA

Question 11

Isocitrate Dehydrogenase is a ___ enzyme and is inhibited by high concentrations of:
Is activated by high concentrations of:

Answer 11

allosteric
ATP and NADH
ADP and NAD+

Question 12

A ___ does not need TPP (although a ___ does)

Answer 12

Beta-decarboxylation

Alpha-decarboxylation

Question 13

Alpha-Ketoglutarate is the ___ to Glutamate

Answer 13

Keto acid

Question 14

Alpha-Ketoglutarate Dehydrogenase

Step 4

Answer 14

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

Question 15

We can add ___ to a C=C to create a hydroxyl group

Answer 15

water

Question 16

Succinyl CoA Synthetase

Step 5

Answer 16

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

Question 17

Synthetase

Answer 17

Same as a Synthase except it requires a nucleotide

Question 18

Succinate is symmetrical so

Answer 18

we cannot tell the difference between arms when tracing radio labels (becomes 1/2)

Question 19

Succinate Dehydrogenase

Step 6

Answer 19

Dehydration of Succinate into Fumarate (trans-form)
Requires: FAD
Produces: FADH2
Reversible

Question 20

Succinate Dehydrogenase contains a ___ prosthetic group that is covalently bonded to a ___ residue which releases its gained electrons into the ___

Answer 20

FAD
His (always attached)
electron transport chain (FADH2)

Question 21

When we go from C-C to C=C we need ___

Answer 21

FAD

Question 22

All reactions of the Citric Acid Cycle occur in the ___, all the enzymes are ___ except for ___ because it is ___

Answer 22

mitochondrial matrix
water soluble proteins
Succinate Dehydrogenase
bound in the membrane

Question 23

Fumarase

Step 7

Answer 23

Hydration of the double bond in Fumarate to form L-Malate
Requires: H2O
Reversible

Question 24

Malate Dehydrogenase

Step 8

Answer 24

The oxidation of L-Malate to form Oxaloacetate
Highly endergonic reaction (+29.7 kJ/mol)
Requires: NAD+
Produces: NADH+H
Reversible

Question 25

Under equilibrium conditions the concentration of Oxaloactetate will be (greater/less) than that of Malate, why?

Answer 25

less

because malate can leave the mitochondria and go on to gluconeogenesis

Question 26

No Acetyl-CoA means a favor toward (Malate/OAA)

Answer 26

Malate

Question 27

There is NO net production of ___

Answer 27

OAA
2 carbons in
2 carbons out

Question 28

From glucose through glycolysis to the TCA cycle what is the net production of ATP

Answer 28

32 ATP
Although it does vary based on what shuttle is used
For this number NADH = 2.5xATP
FADH2 = 1.5xATP