Topic 4: TCA Cycle

Question 1

What does sodium fluoroacetate do to the TCA Cycle?

Answer 1

It binds with OAA to make Fluorocitrate which in turn irreversibly binds to the ACONITASE enzyme at Step 2.

will see Apprehension, restless, wandering, circling seizures, straining to urinate and defecate, Hyperthermia, vomiting, vocalization, rapid rigor mortis

Question 2

What are cofactors of PDH?

Answer 2

NAD+, CoA, Mg++, Thiamine-PP, Lipoic Acid, FAD

Question 3

What vitamins are necessary for PDH?

Answer 3

Thiamine/B1 (for Thiamine-PP), Riboflavin/B2 (for FAD), Niacin/B3 (for NAD), Pantothenic Acid/B5 (for CoA)

Question 4

What’s unique about enzymatic reactions yiedling CO2?

Answer 4

They are energetically irreverisble.

Question 5

What steps of the TCA Cycle yield CO2?

Answer 5

Step 3) Isocitrate dehydrogenase

Step 4) Alph-ketoglutarate dehydrogenase

Question 6

How is PDH turned off?

Answer 6

PDH Kinase with phosphorylate it turning it OFF.

Activated by ATP, Acetyl CoA, NADH (it can tell that PDH has made enough products for the time being)
Deactivated by ADP, CoA-SH, pyruvate, NAD+ (it can tell PDH has work to do)

Question 7

How is PDH turned

Answer 7

PDH Phosphatase will take of phosphate turning it ON.

Activated by Insulin and epinephrine/adrenaline

Question 8

What are some PDH Poisons?

Answer 8

ARSENITE (from Arsenic) screws with disulfide bond on lipoic acid, thereby screwing with anything that uses it, hence PDH.

MERCURY does the same thing.

They ALSO INHIBIT a-KDH at Step 4 in TCA Cycle.

Question 9

What inihibits PDH?

Answer 9

NADH and Acetyl CoA are feedback inhibitors. (Dual action of inhibiting PDH while activating PDH Kinase to deactivate the enzyme entirely)

Question 10

What is Step 1 of TCA Cycle?

Answer 10

Oxaloacetate with Acetyl CoA via Citrate Synthase makes Citrate

Yields CoA-SH and uses H2O.

Inhibited by ATP, Citrate, Fatty Acyl CoA

Question 11

What is Step 2 of TCA Cycle?

Answer 11

Citrate via Aconitase makes Isocitrate

Inhibited by Fluoroacetate

Question 12

What is Step 3 of TCA Cycle?

Answer 12

IsoCitrate via isocitrate dehydrogenase makes alpha-ketoglutarate

Yields NADH and CO2

Inhibited by ATP and NADH

Question 13

What is Step 4 of TCA Cycle?

Answer 13

alpha-ketoglutarate via Alpha-ketoglutarate dehydrogenase makes Succinyl-CoA

Yields NADH and CO2.

Requires Thiamine. Anaplerotic potential

Inhibited by ATP, NADH, Succinyl-CoA, As, and Hg

Question 14

What is Step 5 of TCA Cycle?

Answer 14

Succinyl-CoA via Succinate Thiokinase makes Succinate.

Yields ATP/GTP and CoA-SH. Uses H20.

Question 15

What is Step 6 of TCA Cycle?

Answer 15

Succinate via succinate dehydrogenase makes Fumarate.

Yields FADH2.

This is the enzyme that is the same as Complex 2 in ETC.

Inhibited by OAA. (Malonate too but not normally present in the body, experimentally administered in the past to study TCA Cycle)

Question 16

What is Step 7 of TCA Cycle?

Answer 16

Fumarate via fumarase makes Malate.

Uses H2O.

Question 17

What is Step 8 of the TCA Cycle?

Answer 17

Malate via Malate dehydrogenase makes Oxaloacetate.

Yields NADH. Only enzyme that can work both ways going from OAA to Malate if need be.

Question 18

What are the 5 major outcomes of the TCA Cycle?

Answer 18

1) Major source of carbon dioxide in the body
2) Major source of NADH and FADH2
3) Conversion of excess energy and intermediates to synthesis of glucose and fatty acids
4) Provides precursors for proteins and nucleic acids
5) Its components control directly or indirectly other enzyme systems

Question 19

What intermediates have anaplerotic potential?

Answer 19

Oxaloacetate, alpha-ketoglutarate, Succinyl-CoA (different from Succinate, don’t mix them up), Fumarate

Question 20

What is the rate limiting concentration of the TCA Cycle?

Answer 20

Oxaloacetate.

Question 21

How is TCA Cycle primarily regulated?

Answer 21

Availability of: Oxaloacetate, Acetyl CoA, NAD+, FAD, ADP/GDP, Pi

Also linked to ETC. If the ETC is screwed then so is the TCA Cycle. ATP/ADP Ratio and availability of O2.

Question 22

What would you expect to see in a PDH Deficiency?

Answer 22

elevated Lactate, Pyruvate and Alanine.

Leads to chronic lactic acidosis.

Severe neurological deficits

Question 23

What would you expect to see with Fumarase deficiency?

Answer 23

Encephalopathy and dystonia (abnormal muscle tone).

Abnormal amounts of fumarate in urine.

Autosomal recessive gene.

Question 24

What would you expect to see with a Succinate-DH deficiency?

Answer 24

encephalopathy

Question 25

What is Milk Sickness (aka sick stomach, puking illness, trembles, slows) caused by?

Answer 25

Tremetol, which is a compound found in snakeroot and rayless goldenrod.

Inhibits CITRATE SYNTHASE – Step 1 of TCA Cycle.

Fat soluble and concentrates in milk. Neonates super susceptible

Question 26

What would you expect to see from Milk Sickness/Tremetol toxicity?

Answer 26

KETOACIDOSIS – muscle damage with pain and weakness, ataxia, stiff gait, trembling, constipation, vomiting, salivation, tremors, hepatic necrosis, death