Citric Acid Cycle and Terminal Respiration

Question 1

What is the purpose of the citric acid cycle?

Answer 1

To generate NADH, FADH, carrying electrons for later on

Question 2

How many dehydrogenase reactions occur in the cycle?

Answer 2

4 out of the 8

Question 3

What are the net products of one cycle?

Answer 3

3 NADH, 2 Co2, 1 FADH2, 1 GTP

Question 4

What is the first step of the citric acid cycle?

Answer 4

Oxaloacetate and acetyl CoA bind, and CoA is released, forming citrate.

Question 5

How is the rate of the cycle regulated?

Answer 5

When ATP or NADH levels are high, the cycle is slowed down as we don’t need more energy.
When ADP or NAD+ levels are high, the cycle speeds up as we need energy.

Question 6

What other compound can lead to the formation of Acetyl CoA and why?

Answer 6

Fatty acids. Because when our glucose levels are low glucagon levels rise and break down triglycerides into fatty acids

Question 7

What is the role of insulin?

Answer 7

Insulin regulates our blood sugar level, breaking down sugar into Glc, Fru and Gal

Question 8

What is the role of glucagon? (2)

Answer 8

Stimulates liver to break down glycogen into glucose. Breaks down triglycerides into fatty acids

Question 9

What are other names of the citric acid cycle?

Answer 9

Krebs cycle and Tricarboxyllic acid cycle

Question 10

Where does the citric acid cycle occur?

Answer 10

Mitochondrial matrix

Question 11

How much ATP in total is formed per glucose molecule from products in the Krebs cycle?

Answer 11

24 ATP molecules. 12 in each pyruvate/Acetyl CoA

Question 12

Does the Krebs cycle produce any ATP or O2 directly?

Answer 12

No. Electron carriers use electrons taken from the cycle later to form o2 and ATP

Question 13

Which enzyme converts pyruvate to Acetyl CoA?

Answer 13

Pyruvate dehydrogenase

Question 14

Which process is the conversion of Pyruvate to Acetyl CoA a part of?

Answer 14

Neither glycolysis nor citric acid cycle

Question 15

What is the purpose of the citric acid cycle?

Answer 15

Oxidising Acetyl CoA, releasing CO2 and harvesting electrons along the way

Question 16

What stimulates/inhibits pyruvate dehydrogenase?

Answer 16

High ADP and NAD+ stimulates it. High Acetyl CoA, ATP and NADH inhibit it

Question 17

Where does inhibition of enzymes used in the cycle occur?

Answer 17

At parts of the cycle where CO2 is produced - Decarboxylation.

Question 18

Define amphibolic in terms of the cycle

Answer 18

A pathway which serves both anabolic and catabolic processes.

Question 19

What other products are formed in the cycle and how do they effect the cycle when taken out+ solution?

Answer 19

Proteins, Heme groups and nucleotide bases can be produced from the products of the cycle. However this reduces Oxaloacetate levels, so pyruvate must be converted directly to oxalacetate during gluconeogenesis to restore its levels and allow the cycle to continue.

Question 20

What occurs during terminal respiration?

Answer 20

Electrons enter oxidative phosphorylation, producing H2O and ATP

Question 21

How many protein complexes are involved in the electron transport chain?

Answer 21

4

Question 22

What occurs in complex 1 of ECT?

Answer 22

NADH gives electron to flavin mononucleotide, sending NAD+ back to other processes

Question 23

How do electrons from NADH enter the mitochondrial matrix?

Answer 23

Membrane is impermeable so G3P shuttle takes it to FAD in cell and forms FADH2

Question 24

What are the three ways in which NADH and FADH2 are synthesised?

Answer 24

Glycolysis, citric acid cycle, oxidation of fatty acids in mitochondria

Question 25

What occurs at complex II?

Answer 25

Succinate dehydrogenase enzyme takes electron from FADH2

Question 26

Where do the taken electrons from Complexes 1 and 11 go?

Answer 26

Ubiquinone - a lipid structure

Question 27

What do cytochromes do and what do they include?

Answer 27

They are proteins with heme groups and Fe2+, which accept protons and become Fe3+ before releasing them to the next complex and returning to Fe2+. Includes complex 3, cytochrome C and complex 4

Question 28

What is Complex 3 made from?

Answer 28

Cytochrome b and c1

Question 29

What is complex 4 made from?

Answer 29

Cytochrome a and a3, or known as cytochrome oxidase

Question 30

What happens to the proton gradient as electrons are pushed through the ETC?

Answer 30

Protons are pushed out the matrix, creating a gradient for them to want to come in. The membrane is impermeable, so they must go through protein channels

Question 31

How do protons return to the matrix?

Answer 31

Pass through F0 which is attached to enzyme F1, ATP synthase.

Question 32

How many molecules of ATP can be synthesised by NADH and FADH2?

Answer 32

NADH can synthesise 3 as hydrogen is released at complexes 1, 3 and 4. FADH2 can synthesise only 2 as h+ is only released at complexes 3 and 4

Question 33

What controls the rate of oxidative phosphorylation?

Answer 33

ATP rises, rate decreases. ADP rises, rate increases

Question 34

How does ADP/ATP travel in/out the cell?

Answer 34

ADP/ATP antiport

Question 35

What are the 2 ways that chemicals/drugs can affect oxidative phosphorylation?

Answer 35

Uncoupling and inhibition

Question 36

Explain uncoupling in oxidative phosphorylation

Answer 36

Alternate h+ proton pump is placed on membrane so H+ can flow back in without the ATPase or F0 pump

Question 37

Explain inhibition in oxidative phosphorylation

Answer 37

One of the complexes is inhibited, so no electrons can pass through, preventing H2O from being made and ATP cannot be synthesised. Metabolism slows down