Term
| 1. What is special about Acetyl Co-A |
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Definition
1. Most pathways metabolize fuel sources into the 2 C acetyl part of acetyl Coenzyme A.
- Pyruvate, AAs, FAs, etc all get turned into Acetyl Co-A
2. Aceyl Co-A has many fates and can enter many pathways depending on what the cell needs
3. Acetyl Co-A is the substrate for the TCA |
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Term
2. What happens in the TCA cycle? And what is the main goal?
2.2. What is the goal of the TCA cycle |
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Definition
1. Acetyl Co-A is oxidized to CO2 and H2O
2. Energy of Acetyl Co-A oxidation is conserved through the transfer of electrons to NAD+ and FAD, forming NADH and FADH2.
- This is the main goal of the TCA cycle |
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Term
| 3. What is the outcome of the TCA cycle |
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Definition
1. 3 NADH (1 NADH = 2.5 ATP)
2. 1 FADH2 (1 FADH2 = 1.5 ATP)
3. 1 GTP
4. 2 CO2 molecules (but these are not energy containing compounds)
This results in 9 ATP (after the ETC) and 1 GTP (10 high energy phosphate molecules) for each acetyl group |
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Term
4.1 What is the first step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
4 C Dicarboxylic acid oxaloacetate (OAA) and the acetyl group of Acetyl Co-A condensed to the 6 C Tricarboxylic Acid Citrate
Substrate- 1) OAA & 2) Acetyl Co-A
Product- 1) Tricarboxylic Acid Citrate
Enzyme- 1) Citrate Synthase |
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Term
4.2 What is the second step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Citrate is isomerized to Isocitrate by Aconitase
Substrate- Citrate
Product- Isocitrate
Enzyme- Aconitase |
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Term
4.3 What is the third step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Isocitrate is dehydrogenated to ɑ-Ketoglutarate.
Substrate- Isocitrate
Product- ɑ-Ketoglutarate
Enzyme- Isocitrate Dehydrogenase |
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Term
4.4 What is the fourth step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
ɑ-Ketoglutarate and CoASH react with ɑ-Ketoglutarate dehydrogenase to form Succinyl Co-A
- ɑ Carbon loses CO2
- ɑ Carbon forms bond with Coenzyme A
- NAD+ à NADH (caused by enzyme)
Substrate- 1) ɑ-Ketoglutarate & 2)CoASH
Product- Succinyl Co-A
Enzyme- ɑ-Ketoglutarate dehydrogenase |
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Term
| As electrons move through the TCA Cycle, what happens? |
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Definition
| As electrons move, cofactors are oxidized and reduced |
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Term
4.5 What is the fifth step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Succinyl Co-A and GDP + Pi react with the help of Succinate Thiokinase to form Succinate
- CoASH and GTP are released
- This is an example of substrate level phosphorylation without the use of O2
Substrate- Succinyl Co-A, GDP, Pi
Product- Succinate
Enzyme- Succinate Thiokinase |
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Term
| In the TCA cycle, what energy makes the GTP |
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Definition
| The energy of the Succinyl Co-A thioester bond is used to generate GTP from GDP + Pi |
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Term
| What is substrate phosphorylation |
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Definition
| The formation of a high energy phosphate compound without the use of O2 |
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Term
4.6 What is the sixth step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Succinate is oxidized to Fumarate through Succinate Dehydrogenase
- FAD à FADH2 (1 e- & 1 H+ from each methylene group)
Substrate- Succinate
Product- Fumarate
Enzyme- Succinate Dehydrogenase (Part of the ETC) |
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Term
4.7 What is the seventh step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Water adds across the double bond of Fumarate (with the help of Fumarase) to form Malate
Substrate- Fumarate & H2O
Product- Malate
Enzyme- Fumarase |
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Term
4.8 What is the eighth step of the TCA cycle?
Substrate
Product
Enzyme |
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Definition
Malate is dehydrogenated by Malate Dehydrogenase to Oxaloacetate
Substrate- Malate
Product- Oxaloacetate
Enzyme- Malate Dehydrogenase |
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Term
| 8. What cofactors are essential for TCA function |
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Definition
1. TPP
2. FAD/FMN
3. NADH+
4. Coenzyme A
5. Lipoate
6. Minerals (magnesium, sulfur, and phosphorus) |
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Term
| 5. Why is it important to have tightly coupled reactions in the TCA Cycle |
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Definition
| This allows the cycle to continue moving. The -∆G of certain reactions pull the +∆G forward |
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Term
| 6. What enters the TCA Cycle and what happens to it |
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Definition
Acetyl Co-A enters the TCA cycle. The 2 Carbons come from the acetyl group.
The acetyl is added to Oxaloacetate to form the 6 C Citrate |
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Term
| 7. How do carbon leave the TCA Cycle? |
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Definition
2 Carbons in and 2 Carbons out in the form of 2 CO2 molecules.
- CO2 leaves at the 3rd step (from isocitrate to a-ketoglutarate)
- CO2 leaves at the 4th step (from a-ketoglutarate to Succinyl Co-A)
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Term
What reactions of the TCA have large -∆G?
What does this mean about these reactions? |
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Definition
Formation of
- Citrate
- a-Ketoglutarate
- Succinyl Co-A
These are virtually irreversible because the products from these reactions are used in other reactions |
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Term
| What is the role of Thymine Pyrophosphate (TPP) |
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Definition
- It decarboxylates (kicks a CO2 off of) a-ketoglutarate and takes electrons in the process (it is an electron carrier)
- It passes the electrons to other electron carriers, and the electrons ultimately turn NAD+ to NADH
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Term
| What is substrate level phosphorylation |
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Definition
| The formation of a high energy phosphate compound without the use of O2 |
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Term
| What reactions have +∆G? What does this cause |
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Definition
The accumulation of
- Malate
- Citrate
This causes OAA levels to be low, which controls Acetyl Co-A entry into the TCA cycle |
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Term
| What molecules easily leave the TCA and what do they go on to do? |
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Definition
- (1) Citrate- FA synthesis
- (3) a-Ketoglutarate- AA synthesis
- (4) Succinyl CoA- Heme synthesis
- (7) Malate- Gluconeogenesis
- (8) OAA- AA synthesis
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Term
| Anaplerotic reactions provide the TCA with intermediates. Which one is most important? Why does this happen? |
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Definition
- Pyruvate + CO2 forms OAA
- This happens if OAA is low due to malate accumulation or if Acetyl Co-A levels are high and PDH is turned off (preventing pyruvate from being converted to Acetyl Co-A and entering TCA cycle)
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