The TCA cycle

Question 1

What is the primary function of the TCA cycle

Answer 1

To convert energy available from the oxidization of Acetyl-CoA into 3 molecules of NADH, 1 FADH2 and 1 GTP during each turn
**produces 24 ATP

Question 2

What is the first thing to *enter the TCA?

Answer 2

Citric acid

Question 3

Where is the location of where the TCA takes place?

Answer 3

All cells with mitochondria

Question 4

What causes regulation of the TCA?

Answer 4

Supply and demand of TCA cycle
Availability of NAD and FAD as substrates
Inhibition by NADH
High-energy signals turn off
Low-energy signals turn on

Question 5

What is the role of oxaloacetate in the citric acid cycle?

Answer 5

Its 4 carbon and its what accepts 2 carbons from acetyl-CoA to create citrate which is 6 carbon (first product of TCA)

Question 6

What is created per acetyl-CoA molecule?

Answer 6

You get 3 NADH (9 ATP), 1 FADH2 (2 ATP) and 1 GTP. Since glycolysis produces 2 acetyl-CoA you get double of those.
Total energy yield = 24 per TCA turn

Question 7

what is the total energy produced from glycolysis and the TCA

Answer 7

38
Glyolysis = 8
Pyruvate to Acetly-CoA = 2 NADH = 6 ATP
TCA = 24

Question 8

What does pyruvate dehydrogenase (PDH) do?

Answer 8

It links glycolysis to the TCA cycle. it catalyzes the production of acetyl-CoA which can then ever the TCA as fuel
**the bridge between glycolysis and the TCA

Question 9

Why cant fatty acids contribute to gluconeogenesis?

Answer 9

All fatty acids are broken down to acetyl-CoA inside the mitochondria and we can not turn them into pyruvate, which means they are stuck in the mitochondria and can never be used to start the TCA

Question 10

What is an important regulation site for the TCA cycle?

Answer 10

PDH this is because it regulates the flow of pyruvate into the TCA cycle
**pyruvate dehydrogenase is an important site for regulating energy metabolism

Question 11

What is coenzyme A?

Answer 11

Its an acyl carrier biomolecule, which carries acetyl (2 carbons) or fatty acyl group during TCA cycle and fatty acid synthesis

Question 12

How is CoA synthesized?

Answer 12

Its made from pantothenic acid (vitamin B5), cysteine (amino acid) and ATP

Question 13

What is the main role of CoA?

Answer 13

It transfers fatty acids from the cytoplasm to the mitochondria and when it carries an acetyl group (2 carbon) its known as acetyl-CoA (used for adding 2 carbons and starting TCA)

Question 14

What is pyruvate dehydrogenase and where does it work?

Answer 14

Its found in the mitochondrial matrix which catalyzes the rxn of pyruvate transfering two carbons to CoA to produce acetyl-CoA. It also produces NADH and CO2

Question 15

How many subunits does PDH have ?

Answer 15

It a big complex and has three subunits E1, E2 and E3

It also has a number of cofactors, prosthetic groups and substrates

Question 16

What is TPP?

Answer 16

Its thiamine pyrophosphate

Its a prosthetic group derived from thiamine (B1) which is bound to the E1 subunit of PDH

Question 17

What is lipoic acid/lipoate/lipoaminde?

Answer 17

Prosthetic group that is covalently bound to PDH subunit E2

Question 18

What is coenzyme A?

Answer 18

Derived from vitamin B5, its transiently bound substrate that is linked to the acetyl group of pyruvate. its a coenzyme

Question 19

What is FAD?

Answer 19

Falvin adenine dinucleotide
Derived from vit B2
Its a prosthetic group permanently bound to subunit E3

Question 20

What is NAD?

Answer 20

Nicotinaminde adenine diucleotide
Derived from nicotinic acid (B3)
Transiently bound cofactor

Question 21

How many cofactors are needed in otder to a-ketoglutarate dehydrogenase catalyzed rxn in the TCA cycle?

Answer 21

You need all 5 cofactors

Question 22

What stimulates and inhibits PDH kinase?

Answer 22

High energy state (high NADH, FADH2, ATP) and accumulation of acetyl CoA

Pyruvate (end product of glycolysis) accumulation inhibits PDH

Question 23

What is a thiamine deficiency?

Answer 23

Presentation is beriberi
Lower amounts of thiamine lead to lower thiamine pyrophosphate (TPP) and impaired activity of pyruvate dehydrogenase (PDH) as well as a-ketoglutarte dehydrogenase (of TCA cycle) and transketolase
**very dmging to the heart and brain which have large energy requirements

Question 24

Where is acetyl-CoA mainly present?

Answer 24

In the mitochondria and can not come out to cytoplasm freely

Question 25

What are the three irreversible steps of the TCA cycle?

Answer 25

Citrate synthase

Isocitrate dehydrogenase

a-ketoglutarate dehydrognease

***All blocked in high energy state

Question 26

How is citrate synthase regulated in the TCA?

Answer 26

Inhibitors: ATP, NADH, citrate (product inhibition) and succinyl-CoA (mimics acetyl-CoA, a competitive inhibition)

Question 27

What activates and inhibits Isocitrate Dehydrogenase?

Answer 27

Inhibitors: ATP, NADH
Activators: ADP

Question 28

What inhibits a-ketoglutarate dehydrogenase?

Answer 28

Inhibitors: ATP/GTP, NADH, succinyl-CoA (product inhibition) and arsenic

**uses the same co-factors of pyruvate dehydrogenase

Question 29

What are anaplerotic reactions?

Answer 29

These rxns add to the pool of TCA cycle intermediates at multiple points in the cycle from various dietary precursors

Question 30

What are anabolic reactions?

Answer 30

Use the TCA cycle intermediates to make other important biomolecules