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Metabolism > The TCA Cycle > Flashcards

The TCA Cycle Flashcards

1
Q

Where does the TCA cycle happen?

A
  • Everywhere and in all tissues requiring energy in the fed state
  • Except RBC because there are no mitochondria
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2
Q

What is the common end product of carbohydrate, fatty acid and amino acid metabolism?

A

Acetyl CoA

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3
Q

What is acetyl CoA used for the biosynthesis of in the cytoplasm?

A
  • Fatty acids
  • Ketone bodies (only in the liver)
  • Cholesterol
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4
Q

Where can it be stored for use in the TCA cycle and why?

A
  • Mitochondrial matrix

- Too big to cross inner mitochondrial matrix

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5
Q

What is acetyl CoA converted to in the TCA cycle (step 1)?

A
  • Citrate (6 carbons)
  • Combines with oxaloacetate
  • Condensation reaction
  • Citrate synthase
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6
Q

What is released in step 1 of TCA cycle?

A
  • Water

- CoA

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7
Q

What is citrate converted to in TCA cycle (step 2)?

A
  • Isocitrate (6 carbons)

- Slight modification of the structure

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8
Q

What is isocitrate converted to in TCA cycle (step 3)?

A
  • α-ketoglutarate
  • 5 carbon molecule
  • Enzyme: isocitrate dehydrogenase
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9
Q

What is released in step 3 of TCA cycle (isocitrate–> α-ketoglutarate)?

A
  • NADH (reduced from NAD+)

- One carbon dioxide molecule

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10
Q

What inhibits isocitrate dehydrogenase?

A
  • High levels of NADH or ATP in the cell
  • Slows down turning of TCA cycle
  • When active it donates electrons from isocitrate to NAD
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11
Q

What is α-ketoglutarate converted to in TCA cycle (step 4)?

A
  • Succinyl CoA
  • 4 carbon molecule
  • CoA temporarily re-introduced
  • Enzyme: α-ketoglutarate dehydrogenase
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12
Q

What is released in step 4 of the TCA cycle (α-ketoglutarate –> succinyl CoA)?

A
  • NADH (reduced from NAD)

- Carbon dioxide molecule

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13
Q

What is succinyl CoA converted to in TCA cycle (step 5)?

A
  • Succinate
  • CoA quickly lost
  • No enzyme
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14
Q

What is released in step 5 of the TCA cycle (succinyl CoA–> succinate)?

A
  • CoA

- GTP (GDP + Pi)

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15
Q

What is succinate converted to in TCA cycle (step 6)?

A
  • Fumarate
  • 4 carbon molecule
  • Enzyme: succinate dehydrogenase
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16
Q

What is released in step 6 of the TCA cycle (succinate to fumarate)?

A
  • FADH (reduced from FAD)
17
Q

What is fumarate converted to in TCA cycle (step 7)?

A
  • Malate- 4 carbons
  • Enzyme: Fumarase
  • Fumarate + water
18
Q

What is malate converted to in the TCA cycle (step 8)?

A
  • Oxaloacetate
  • 4 carbon
  • Enzyme: malate dehydrogenase
19
Q

What is released in step 8 of TCA cycle (malate to oxaloacetae)?

A
  • NADH (Reduced from NAD+)
20
Q

What happens to all the NADH/FADH molecules released from TCA cycle?

A
  • Become electron donors in the electron transport chain
  • One molecule of FADH2
  • 3 molecules of NADH (each accepting 2 electrons)
21
Q

What are the two major flavin redox coenzymes?

A
  • Flavin adenine dinucleotide (FAD)

- Flavin mononucleotide (FMN)

22
Q

How many electrons and protons do FAD and FMN accept?

A
  • 2 electrons
  • 2 protons
  • For molecules undergoing metabolism
23
Q

What vitamin do FAD and FMN both contain

A
  • Riboflavin-5’-phosphate

- Produced from vitamin B2 (riboflavin)

24
Q

What is meant by ‘anaplerotic reactions’?

A
  • Filling up reactions

- Intermediates of the TCA cycle solely for use of the TCA cycle

25
Q

What other reactions is oxaloacetate used for?

A
  • Amino acids synthesis (non-essential ones as they can be formed in the body)
26
Q

What other reactions is α-ketoglutarate used for?

A
  • Amino acid synthesis

- Neurotransmitter synthesis in the brain

27
Q

What other reaction is malate used for?

A
  • Gluconeogenesis
28
Q

What other reaction is succinyl CoA used for?

A
  • Haem synthesis
29
Q

What other reaction is citrate used for?

A
  • Fatty acid synthesis
30
Q

What are glucogenic and ketogenic type amino acids?

A
  • Able to join the TCA cycle at different points

- Amino acids can go into TCA cycle and help replenish intermediates- they can be converted to convenient molecules

31
Q

What processes are glycogenic and ketogenic amino acids used for when removed from TCA cycle?

A
  • Gluconeogenesis

- Ketogenesis (by forming acetyl CoA)

32
Q

What does the ‘link reaction’ convert pyruvate into?

A

Acetyl CoA

33
Q

How can pyruvate be directly inserted into the TCA cycle?

A
  • Converted directly into oxaloacetate
  • Requires some energy
  • Pyruvate carboxylase is used for this reaction
34
Q

Describe the structure of ATP?

A
  • Adenine
  • Ribose sugar
  • 3 phosphate groups
35
Q

Describe stage 1 of fuel oxidation

A
  • Production of reduced nucleotide coenzymes during oxidation of fuels and the release of carbon dioxide
  • Reduced enzymes include NADH and FADH2
36
Q

Describe stage 2 of fuel oxidation

A
  • When electron carriers are passing electrons into electron transport chain
  • Oxygen required
  • ATP generated from free energy provided by oxidation of reduced coenzymes

Metabolism (9 decks)

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