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Biochemistry II > Kreb's Cycle > Flashcards

Kreb's Cycle Flashcards

1
Q

What are some other names for the Kreb’s Cycle?

A
  • The citric acid cycle

- The TCA (tricarboxylic acid cycle)

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2
Q

What is the purpose of the Kreb’s Cycle?

A
  • Takes in fat, carbs, and protein and oxidizes them with dehydrogenase enzymes
  • NADH and FADH2 is produced, which then deliver electrons to the electron transport system to make ATP
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3
Q

When do carbohydrates enter the Kreb’s cycle? What molecule enters?

A
  • Carbs enter after running through glycolysis and a prep step
  • Acetyl CoA is the molecule that enters
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4
Q

When do fats enter the Kreb’s cycle? What molecule enters?

A
  • Fats enter after running through Beta Oxidation

- Acetyl CoA is the molecule that enters

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5
Q

When do proteins enter the Kreb’s cycle?

A

Each amino acid is unique how it enters the Kreb’s cycle

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6
Q

What does the preparation step of the Kreb’s cycle consist of?

A
  • Pyruvate is shuttled into the mitochondria
  • Pyruvate undergoes oxidative decarboxylation with the help of pyruvate dehydrogenase
  • CO2 is produced and NAD+ is converted to NADH
  • Acetyl CoA is created
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7
Q

This reaction takes place in the mitochondrial matrix and is the oxidation of fatty acids where a two carbon molecule (acetyl CoA) is cleaved off the fatty acid.

A

Beta Oxidation

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8
Q

What is the main enzyme for beta oxidation?

A

Acyl CoA dehydrogenase

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9
Q

This coenzyme consists of pantothenic acid and a terminal thiol group, it forms high energy thioester bonds with acetic acid and fatty acids, and is used in fatty acid synthesis and oxidation, pyruvate oxidation, and acetylation.

A

Coenzyme A

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10
Q

What is the entry point reaction for the Kreb’s cycle?

A

Acetyl CoA and Oxaloacetate are converted into citric acid with the help of citrate synthase, water, and the breaking off of coenzyme A

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11
Q

After the entry point reaction of the Kreb’s cycle isomerization occurs to convert citric acid into what?

A
  • Aconitase isomerizes citric acid into Cis-Aconitate (unstable intermediate) through the removal of H2O
  • When H2O is added cis-aconitate is converted into isocitric Acid
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12
Q

After citric acid is isomerized into isocitric acid, what happens next in the Kreb’s cycle?

A
  • Isocitrate dehydrogenase oxidizes isocitric acid into oxalosuccinate (unstable intermediate) through the conversion of NAD+ to NADH
  • When CO2 is removed from this reaction oxalosuccinate is converted into alpha-ketoglutarate using isocitrate dehydrogenase
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13
Q

After alpha-ketoglutarate is formed, what is the next step in the Kreb’s cycle?

A
  • alpha-keoglutarate dehydrogenase complex converts alpha-ketoglutarate to succinyl CoA
  • During this step NAD+ is converted to NADH, coenzyme A is used, and CO2 is released
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14
Q

After Succinyl CoA is formed, what is the next step in the Kreb’s cycle?

A
  • Succinate thiokinase (succinyl CoA synthetase) converts succinyl CoA to succinate
  • GTP is formed during this step and coenzyme A is used
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15
Q

How is GTP converted to ATP?

A
  • GTP + ADP GDP + ATP

- Nucleotide diophosphokinase is the enzyme utilized

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16
Q

After succinate is formed, what is the next step in the Kreb’s cycle?

A
  • Succinate dehydrogenase converts succinate to fumarate through oxidation
  • FAD is converted to FADH2
17
Q

After fumarate is formed, what is the next step in the Kreb’s cycle?

A

Fumarase converts fumarate to malate through hydration

18
Q

After malate is formed, what is the next step in the Kreb’s cycle?

A
  • Malate dehydrogenase converts malate to oxaloacetate through oxidation
  • NAD+ is converted to NADH
  • This is the final step in the Kreb’s cycle before it begins again
19
Q

What is the ultimate acceptor of electrons?

A

Oxygen

20
Q

What does anaplerotic mean?

A

Giving substrates to the Kreb’s cycle

21
Q

What does cataplerotic mean?

A

Taking substrates from the Kreb’s cycle

22
Q

These enzymes control the rate of the Kreb’s cycle, but can be influenced.

A
  • Pyruvate dehydrogenase
  • Citrate synthase
  • Isocitrate dehydrogenase
  • Alpha KG dehydrogenase
23
Q

What factors can inhibit pyruvate dehydrogenase?

A
  • High NADH/NAD+
  • High Acetyl CoA/CoA
  • High ATP/ADP
24
Q

What factors can inhibit citrate synthase?

A
  • ATP allosterically inhibits it

- Lack of oxaloacetate

25
Q

What two factors can regulate isocitrate dehydrogenase?

A
  • Energy charge (ATP inhibits, ADP stimulates)

- Redox state (NADH inhibits, NAD+ stimulates)

26
Q

What factors can regulate alpha KG dehydrogenase?

A

Energy Chage:

  • ATP inhibits
  • NADH inhibits
  • Succinyl CoA inhibits
27
Q

What are the final common products of the aerobic metabolism of carbohydrates, fats, and proteins?

A

Carbon dioxide and water

28
Q

What is the purpose of the Kreb’s cycle?

A

Make ATP and reduced compounds

29
Q

The Kreb’s cycle is the common pathway for what substances?

A
  • Fats
  • Carbohydrates
  • Proteins
30
Q

Where does the Kreb’s cycle take place?

A

Mitochondrial matrix

31
Q

The Kreb’s cycle contains numerous amounts of these reactions.

A

Oxidation/reduction reactions

32
Q

What does the Kreb’s cycle send to the electron transport chain?

A

Reduced compounds (NADH and FADH2)

33
Q

Products ____ and reactants ____ the Kreb’s cycle.

A

Inhibit; stimulate

34
Q

What are the main enzymes of the Kreb’s cycle?

A
  • Isocitrate dehydrogenase
  • Alpha ketoglutarate dehydrogenase
  • Succinate dehydrogenase
  • Malate dehydrogenase
35
Q

What products inhibit the Kreb’s cycle?

A
  • ATP
  • High energy charge
  • NADH
  • FADH2
36
Q

What reactants stimuluate the Kreb’s cycle?

A
  • ADP or AMP
  • Low energy charge
  • NAD+
  • FAD

Biochemistry II (16 decks)

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