TCA Cycle

Question 1

Where does the TCA cycle occur?

Answer 1

All reactions occur in mitochondria

Question 2

What are the products of the TCA cycle?

Answer 2

• NADH
• FADH2 -> ETC (ATP)
• GTP
• CO2

Question 3

What is Citrate synthesised from?

Answer 3

• Acetyl CoA (2C)

- Oxaloacetate (4C)

Question 4

What enzyme synthesises citrate?

Answer 4

Citrate Synthase

Question 5

What can inhibit citrate synthase?

Answer 5

ATP

Question 6

What does citrate inhibit?

Answer 6

PFK1

Question 7

What does citrate activate?

Answer 7

ACoA carboxylase (fatty acid synthesis)

Question 8

What is used for gluconeogenesis in the fasting state?

Answer 8

Oxaloacetate

this lowers the amount able to be used for TCA cycle

Question 9

How is ketone synthesis triggered in the fasting state?

Answer 9

Oxaloacetate used for gluconeogenesis

• Less acetyl coA used for TCA cycle, build up
• Excess acetyl coA converted into ketones

Question 10

What is isocitrate to citrate?

Answer 10

An isomer

Question 11

What enzyme converts citrate to isocitrate?

Answer 11

Aconitase

Question 12

What does fluoroacetate (rat poison) inhibit?

Answer 12

Aconitase

- Citrate -> Isocitrate

Question 13

What is the rate-limiting step of the TCA cycle?

Answer 13

• Isocitrate
  -> Co2 NADH
  -> Alpha-ketoglutarate
  (Enzyme: Isocitrate Dehydrogenase)

Question 14

What enzyme converts Isocitrate to alpha-ketoglutarate?

Answer 14

Isocitrate Dehydrogenase

- Rate-limiting step

Question 15

What inhibits alpha-Ketoglutarate?

Answer 15

• ATP

- NADH

Question 16

What activates alpha-Ketoglutarate?

Answer 16

• ADP

- Ca2+

Question 17

What are the irreversible steps of the TCA cycle?

Answer 17

Citrate synthase (oxaloacetate -> Citrate)

Isocitrate dehyrogenase
(Isocitrate -> alpha-ketoglutinate)

alpha ketoglutinate dehydrogenase
(a-KG -> Succinyl CoA)

Question 18

What enzyme converts alpha ketoglutarate to Succinyl-CoA?

Answer 18

alpha-KetoGlutinate Dehydrogenase

Question 19

What inhibits alpha-KetoGlutinate Dehydrogenase ?

Answer 19

• Succinyl-CoA (product)

- NADH

Question 20

What stimulates alpha-KetoGlutinate Dehydrogenase ?

Answer 20

Ca2+

Question 21

What is taken off of alpha ketoglutarate and added to it to make Succinyl-CoA?

Answer 21

• CoA added

- CO2 and NADH taken off

Question 22

What is taken off of Succinyl-CoA to make Succinate?

Answer 22

• CoA

- GTP

Question 23

What enzyme converts succinyl-CoA into Succinate?

Answer 23

Succinyl-CoA synthase

Question 24

What enzyme converts Succinate to fumarate?

What is significant?

Answer 24

Succinate dehydrogenase

• Embedded in mitchondrial membrane
• Function as complex II electron transport

Question 25

What molecule is also produced from Succinate dehydrogenase?

Answer 25

FADH2 (FAD+ the other way)

Question 26

What other pathways (other than TCA) can produce fumarate?

Answer 26

- Urea cycle - Purine synthesis (formation of IMP) - Amino acid breakdown (phenylalanine, tyrosine)

Question 27

What converts malate into fumarate?

Answer 27

Fumarase

Question 28

What converts Malate into NADH and Oxaloacetate?

Answer 28

Malate dehydrogenase

Question 29

What are the 2 major functions of malate/

Answer 29

- Transfer of NADH into mitochondria | - Transfer of oxaloacetate OUT of mitochondria

Question 30

How does malate transfer NADH?

Answer 30

Oxaloacetate -> Malate NADH-> NAD+ (electrons donated to malate) - Malate then transported into mitochondria - Malate converted to oxaloacetate making a molecule of NADH from NAD+

Question 31

How is oxaloacetate replinshed in the cytosol when used in malate shuttle?

Answer 31

Oxaloacetate converted to aspartate (Glut-> a-KG) - Aspartate then shuttled across - Aspartate trnasfered to OAA (glut-> a-KG)

Question 32

Describe how oxaloacetate can be transfered out of the mitochondria to participate in gluconeogensis?

Answer 32

OAA -> Malate (NADH -> NAD+) - Malate transfered out of mitochondria - Malate converted to OAA (NAD+ -> NADH)

Question 33

What is citrate also used for?

Answer 33

Fatty acid synthesis

Question 34

What is alpha-Ketoglutarate also used for?

Answer 34

Amino acid synthesis

Question 35

What is Oxaloacetate also used for?

Answer 35

- Amino acid synthesis | - Glucose

Question 36

What can succinyl coA be used for other than TCA cycle?

Answer 36

Heme synthesis

Question 37

What can Succinyl-CoA be synthesised from?

Answer 37

- Methylmalonyl coA (from odd chain fatty acids and branched chain amino acids) - a-KG (TCA cycle)

Question 38

What are all the inhibitors of the TCA cycle?

Answer 38

- ATP - NADH - Acetyl-CoA - Citrate - Succinyl CoA Signs of high energy

Question 39

What is the TCA cycle activated by?

Answer 39

Ca2+ and ADP