Citric Acid Cycle

Question 1

What two processes use an enzymatic activity called pyruvate dehydrogenase complex to convert pyruvate from glycolysis to acetyl coA for the citric acid cycle?

Answer 1

Oxidative decarboxylation (in higher cells) and non-oxidative decarboxylation (in yeast).

Question 2

Pyruvate dehydrogenase complex is in what organelle and requires what from the cytoplasm to be transported in?

Answer 2

Is in the mitochondrion and requires pyruvate from the cytoplasm.

Question 3

What are the names of the three units in the pyruvate dehydrogenase complex?

Answer 3

-Pyruvate decarboxylase (E1) -Dihyrolipoamide transacetylase (E2) -Dihyrolipoamide dehydrogenase (E3)

Question 4

What does the E1 of pyruvate dehydrogenase complex do?

Answer 4

It decarboxylates pyruvate, and starts its oxidation (oxidative decarboxylation of pyruvate) using TPP

Question 5

What does E2 of pyruvate dehydrogenase complex do?

Answer 5

Oxidation ends in E2 and the reactive molecule (acetyl group) is passed to CoA to make Acetyl CoA using Lipoamide

Question 6

What does E3 of pyruvate dehydrogenase complex do?

Answer 6

handles electrons (via FAD) and regenerates the enzyme (oxidized form of lipoamide).

Question 7

What are the five coenzymes used by the pyruvate dehydrogenase complex?

Answer 7

-TPP (Thiamine pyrophosphate) -Lipoamide -NAD -FAD -Coenzyme A (also called CoAsh/CoA)

Question 8

The reaction catalyzed by pyruvate dehydrogenase complex is similar to what? and why?

Answer 8

Similar to alpha-keto-glutarate dehydrogenase complex of citric acid cycle because both involve alpha-keto acids.

Question 9

Describe the reaction mech in aerobic higher organisms in pyruvate dehydrogenase complex.

Answer 9

-Bind pyruvate by an ionized TPP -decarboxylation -transfer to lipoamide -linkage of acetyl group to CoA/CoASH to form acetyl-CoA

Question 10

After acetyl CoA is formed in the reaction mechanism in the pyruvate dehydrogenase complex, what happens to the electrons in the system?

Answer 10

-electrons are transferred from the oxidation of FAD (forming FADH2). -electrons are transferred from FADH2 to NAD+ to form NADH and return FADH2 to FAD.

Question 11

How is the reaction mechanism in pyruvate dehydrogenase complex different in yeast formation?

Answer 11

It stops at the decarboxylation step to form acetealdehyde without loss/gain of electrons. There is no reduction/oxidation.

Question 12

What happens to acetealdyhyde is yeast?

Answer 12

It is converted to ethanol.

Question 13

When oxygen is present in yeast, does fermentation occur?

Answer 13

No, activities of E2 and E3 catalyze reactions just like animal cells and produce acetyl CoA.

Question 14

Where does oxidation mostly occur? What do byproducts of this of oxidation result in?

Answer 14

-Mitochondria -Damaged mitochondia

Question 15

Where does citric acid cycle occur? How many carbons are added from acetyl coA and how many carbons released?

Answer 15

-mitochondial matrix -two carbons are added from acetyl CoA and two carbons are released as carbon dioxide.

Question 16

How many NADH and FADH2 are produced in the citric acid cycle? What other molecule is produced?

Answer 16

three NADH and one FADH2 are produced. Another higher energy phosphate (GTP in animals, ATP is plants/bacteria) are produced per acetyl CoA.

Question 17

One molecule of glucose yields how many acetyl CoAs for the Citric acid cycle?

Answer 17

two acetyl CoAs

Question 18

When do the two carbons from acetyl CoA at the beginning of the cycle become oxidized to CO2?

Answer 18

Not until the beginning of the second time around the cycle.

Question 19

What are the two main parts of the citric acid cycle?

Answer 19

• release of CO2
• conversion to oxaloacetate

Question 20

Describe the first part of the beginning of citric acid cycle:

Answer 20

-The enzyme citrate synthase catalyzes joining of (4C) oxaloacetate and (2C) acetyl CoA -Makes a activated intermediate (6C) Citryl CoA -Intermediate then becomes (6C) Citrate.

Question 21

Is the first part of the citric acid cycle very favorable? Why and what does it help do?

Answer 21

Yes it is, due to the breaking of thioester bond in acetyl CoA. This favorability pulls the unfavorable reaction preceding it.

Question 22

Describe the second part of the beginning of the citric acid cycle:

Answer 22

The enzyme aconitase rearranges the (6C) citrate to make an intermediate cis-Aconitate that then becomes (6C) isocitrate.

Question 23

What inhibits aconitase and what has it been used for?

Answer 23

Aconitase is inbihited by fluorocitrate. Fluoroacetate is a poison (used to kill cayotes) that can be used by citrate synthase to make fluorocitrate.

Question 24

How many electrons come off total in citric acid acid? What is it more efficient than?

Answer 24

8 e- come off in pairs via 4 reduced electron carriers and GTP. It is more efficient than glycolysis.

Question 25

What is the next step after isocitrate is produced (2 things produced) ? What enzyme is used?

Answer 25

The enzyme dehydrogenase catalyzes the first decarboxylation and produces NADH and alpha ketoglutarate (5C since CO2 released).

Question 26

Why is alpha ketoglutarate an important intermediate?

Answer 26

It is involved in anaplerotic reaction related to transamination.

Question 27

What is the mechanism of the enzyme acting on alphaketo glutarate (alpha keto gluterate dehydrogenase complex) vitually identical to?

Answer 27

Identical to the mechanism in the pyruvate dehydrogenase complex and involves the same coenzymes.

Question 28

What are the products of the mechanism of alpha ketogluterate dehydrogenase complex?

Answer 28

(4C in middle) Succinyl-CoA and NADH

Question 29

What is the enzyme of the product of the only substrate level phosphorylation in the citic acid cycle after the step where Succinyl CoA is produced?

Answer 29

The enzyme succinyl-CoA synthetase used to produce GTP and (4C) succinate.

Question 30

After succinate is produced, what enzyme is used for the next step and what is the product?

Answer 30

Succinate dehydrogenase (contains a covalently linked FAD electron carrier). The products are FADH2 and fumarate.

Question 31

The reaction from succinate to fumarate using succinate dehydrogenase has what sort of energetic favorability and what is the consequence of this?

Answer 31

allows for the reaction to have a delta G0' of zero and the reaction is reversible to produce succinate.

Question 32

After fumerate is produced, what is used and produced for the next step?

Answer 32

Water is added to fumarate (catalyzed by fumerase) to make L-malate.

Question 33

What happens after L-malate is created? Is it energetically favorable?

Answer 33

-malate dehydrogenase yields NADH and oxaloacetate. It is energeically unfavorable and is the only bump in the citric acid cycle.

Question 34

How is the bump/energetically unfavorable reaction overcome?

Answer 34

By the pulling of citrate synthase reaction that makes oxaloacetate concentrations low.

Question 35

What happens after (4C) L-malate is created?

Answer 35

It uses malate dehydrogenase to produce (4C) oxoaloacetate.

Question 36

What is the most important way that the citric acid cycle is regulated? Why?

Answer 36

The amount of NAD+ and FAD that is available. They are essential for the citric acid cycle and for the pyruvate dehydrogenase complex complex reaction?

Question 37

When all NADHs and FADH2s are converted to ATP how many ATPs are yielded per molecule of glucose? How does this compare to that yielded by glycolysis under anaerobic conditions?

Answer 37

Yields 30-38 ATP per glucose compared to the 2 from glycolysis.

Question 38

When NAD+ levels are high is the citric acid cycle favored or not?

Answer 38

It is favored. When NADH is high, it stops because NAD+ is not as abundant.

Question 39

Why is oxygen a limiting reagent in the citric acid cycle?

Answer 39

Oxygen is required for converstion of NADH to NAD+ later on.

Question 40

What is the difference between glycolysis and citric acid cycle when it comes to oxygen needs?

Answer 40

Glycolysis can use fermentation to get around needing oxygen while citric acid cycle cannot. It needs NAT+ in three of its reactions.

Question 41

What is sensitive to arsenite and mercury due to the fact that the compounds react with sulfur atoms in lipoamide of this complex? What is the treatment?

Answer 41

- pyruvate dehydrogenase because has lipoamide in E3 of pyruvate dehydrogenase complex. - Can be treated with BAL which extracts arsenite from lipoamide since it also contains sulfurs that bind to arsenite.

Question 42

What are anaplerotic reactions? Two things that are important for this in citric acid cycle?

Answer 42

Reaction involved in "filling up" of the intermediates of metabolism, which are needed for multipurposes. -oxaloactate and alpha ketoglutarate

Question 43

Examples of anaplerotic reaction: Example of its correction:

Answer 43

- oxaloacetate used by making asparitc acid and must be replenished - Conversion of glutamic acid to alpha ketoglutarate to then convert this to oxaloacetate.

Question 44

What are citric acid cycle intermediates involved in?

Answer 44

metabolism of amino acids, fatty acids, mucleotides, and sugars.

Question 45

What are the other metabolic pathways of oxaloacetate?

Answer 45

- converted to glucose in gluconeogenisis - converted to aspartate by transmination - converted to citrate in the citric acid cycle

Question 46

What is the Glycoxylate cycle? What does it not do?

Answer 46

- pathway like citric acid cycle used in plants and bacteria and produces less NADH. - Does not do decarboxylation

Question 47

Two additional enzymes and their roles in glyoxylate cycle:

Answer 47

- isocitrate lyase catalyzes cleavage of isocitrate to glycoxylate and succinate - malate synthase catalyzes linkage of avetyl-CoA to glyoxylate to form malate

Question 48

The bypassing of decarboxylation in the glycoxylate cycle allow for what in plants and bacteria?

Answer 48

Allows them to make glucose in net amounts (more glucose) and not as much ATP.

Question 49

If plant cells need energy what will the run? If plant cells have enough energy what will they run?

Answer 49

- Citric acid cycle that will make more ATP and make fatty acids. - Glycoxylate cycle where they can make glucose instead of fatty acids (this is why plants dont get fat).