bmsc 230 module 6 citric acid cycle

What are other common names for the citric acid cycle?

TCA cycle and Krebs cycle

What is the citric acid cycle?

completes the breakdown of glucose

Where does the TCA cycle occur?

mitochondrial matrix

What does acetyl CoA combine with in the citric acid cycle?

Oxaloacetate to make a 6 Carbon intermediate

Net reaction of TCA cycle?

acetyl CoA + 3NAD+ + FAD + GDP + Pi + H20 --> 3NADH + FADH2 + GTP + CoA + 2CO2

What are the products of TCA?

3 NADH
1 FADH2
1 GTP
2 CO2

What is oxidative phosphorylation?

Uses energy released by the electron transport chain to power ATP synthesis.

Where are the enzymes for the TCA cycle?

all are floating in mitochondrial matrix except one is bound to the inner mitochondrial matrix

Step 1 of TCA cycle? Cofactors?

Oxaloacetate --> Citrate

Cofactors: Acetyl CoA --> + CoA

What enzyme catalyzes step 1 of TCA cycle?

Citrate Synthase

What kind of reaction is step 1 of TCA cycle?

Condensation

Step 2 of TCA cycle? Cofactors?

Citrate --> Isocitrate

Cofactors: H2O --> H20

What enzyme catalyzes step 2 of TCA cycle? what happens?

aconitase. removes water molecule and reattch at different carbon

What kind of reaction is step 2 of TCA cycle?

Dehydration, rehydration

Step 3 of TCA cycle? Cofactors?

isocitrate --> alpha-ketoglutarate

Cofactors: NAD+ --> NADH + CO2

What enzyme catalyzes step 3 of TCA cycle?

isocitrate dehydrogenase

What kind of reaction is step 3 of TCA cycle?

oxidative and decarboxylation

Step 4 of TCA cycle? Cofactors?

alpha-ketoglutarate --> succinyl-coA

Cofactors: NAD+ + CoA --> NADH + CO2

What enzyme catalyzes step 4 of TCA cycle?

alpha-ketoglutarate dehydrogenase complex

What kind of reaction is step 4 of TCA cycle?

Oxidative decarboxylation

Step 5 of TCA cycle? Cofactors?

succinyl-CoA --> succinate

Cofactors: ADP + Pi --> ATP + CoA

What enzyme catalyzes Step 5 of TCA cycle?

succinyl-CoA synthetase

What kind of reaction is step 5 of TCA cycle?

substrate level phosphorylation

Step 6 of TCA cycle? Cofactors?

succinate --> fumarate

Cofactors: FAD --> FADH2

What enzyme catalyzes step 6 of TCA cycle?

Succinate dehydrogenase

What kind of reaction is step 6 of TCA cycle?

Dehydrogenation

Step 7 of TCA cycle? Cofactors?

fumarate --> malate

Cofactors: H20

what enzyme catalyzes step 7 of TCA cycle?

fumarase

what kind of reaction is step 7 of TCA cycle?

hydration

Step 8 of TCA cycle? Cofactors

malate --> oxaloacetate

Cofactors: NAD+ --> NADH

What enzyme catalyzes step 8 of TCA cycle?

Malate Dehydrogenase

What kind of reaction is step 8 of TCA cycle?

Dehydrogenation

One turn of the TCA cycle

-two carbons enter
(acetyl CoA)
-2 carbons leave via 2 CO2 from oxaloacetate
-3 NADH
-1 FADHS
-1 GTP = ATP
-Oxaloacetate regenerated

what does the oxidation of glucose yield?

2 pyruvate

How many ATP does NADH yield?

2.5 ATP

How many ATP does FADH2 yield?

1.5 ATP

What regulates the TCA cycle?

1. phosphorylation of pyruvate dehydrogenase

2. TCA cycle enzymes. the two irreversible reactions

what reactions are not reversible in TCA cycle?

-isocitrate dehydrogenase
-alpha-ketoglutarate dehydrogenase

activators and inhibitors of isocitrate dehydrogenase

Activators: ADP

Inhibitors: ATP and NADH

Inhibitors of alpha-ketoglutarate dehydrogenase

ADP, Succinyl CoA, NADH

What can Citrate be used for other than the TCA cycle?

Fatty acids and sterols

What can alpha-ketoglutarate be used for other than the TCA cycle?

Glutamate --> other amino acids --> Purines

What can Succinyl CoA be used for other than the TCA cycle?

Porphyrins, heme, chlorophyll

What can Oxaloacetate be used for other than the TCA cycle?

Amino acids

What are anaplerotic reactions?

Reactions that replenish citric acid cycle intermediates

Anaplerotic carboxylase reaction in TCA cycle

Pyruvate carboxylase (idk)

Pyruvate undergoing carboxylation to make oxalaoacetate

What does fluoroacetate do to the TCA cycle?

inhibits aconitase and the formation of isocitrate

Why is the inhibition of aconitase detrimental?

blocks the TCA cycle
accumulation of Citrate and energy depletion
seizures

What is the glyoxylate cycle?

It is similar to the citric acid cycle but bypasses the two decarboxylation steps, allowing the synthesis of carbohydrates from fats

When is the glyoxylate cycle highly active in oil seed plants?

During germination because it helps synthesize energy before they can photosynthesize

Where does the glyoxylate cycle occur?

glyoxysomes

Glyoxylate cycles main function?

produce succinate to be converted to oxaloacetate and then into glucose

Step 1 of glyoxylate cycle? Cofactors?

oxaloacetate --> Citrate

Cofactors: Acetyl CoA + H20 --> CoA

What enzyme catalyzes step 1 of glyoxylate cycle?

Citrate Synthase

Step 2 of glyoxylate cycle? Cofactors?

Citrate --> Isocitrate

Cofactors: H20 --> H20

What enzyme catalyzes step 2 of glyoxylate cycle? What happens?

Aconitase. Removes water molecule and reattach at different carbon

What kind of reaction is step 2 of the glyoxylate cycle?

Dehydration, Rehydration

Step 3 of glyoxylate cycle?

Isocitrate --> Succinate + Glyoxylate

What happens to the succinate produced in the glyoxylate cycle?

Goes into the mitochondria and enters the citric acid cycle

What enzyme catalyzes step 3 of the glyoxylate cycle?

Isocitrate lyase

What does a lyase enzyme do?

One molecules is broken down into two

Step 4 of glyoxylate cycle? Cofactors?

Glyoxylate --> Malate

Cofactors: Acetyl CoA + H20 --> CoA

What enzyme catalyzes step 4 of the glyoxylate cycle? what happens?

Malate Synthase. Glyoxylate condenses with acetyl CoA

Step 5 of the glyoxylate cycle? Cofactors?

Malate --> Oxaloacetate

Cofactors: NAD+ --> NADH + H+

What enzyme catalyzes step 5 of the glyoxylate cycle? what happens?

Malate dehydrogenase. Malate is oxidized

What reactions are bypasses in the glyoxylate cycle?

Isocitrate dehydrogenase and the alpha-ketoglutarate dehydrogenase reactions

What does one cycle of the glyoxylate cycle use and produce?

2 Acetyl CoA and produces 1 succinate

What 4 pathways are involved in conversion of fat to glucose in plants?

1. Fatty Acid Oxidation to generate Acetyl CoA (glyoxysomes)
2. Glyoxylate cycle (Glyoxysome)
3. TCA cycle (mitochondria)
4. Gluconeogenesis (Cytoplasm)

Glyoxylate cycle and Citric Acid cycle overall reactions?

(Lipid Body) TAG--> FA --(Glyoxysome)--> Acetyl CoA--> Succinate-- (Mtio) --> Malate --(Cytoplasm)--> Oxaloacetate --> Glucose

What are the two different enzymes in the glyoxylate cycle compared to the TCA cycle?

Isocitrate lyase and Malate synthase