Pyruvate Oxidation (3)

Question 1

Q: What led to the endosymbiotic relationship between eukaryotes and mitochondria?

Answer 1

A: The phagocytosis of an aerobic prokaryotic cell by a eukaryotic ancestor led to the endosymbiotic relationship between eukaryotes and mitochondria observed today.

Question 2

Q: What evidence supports the endosymbiotic theory regarding mitochondria?

Answer 2

A: Mitochondria contain their own DNA and replicate within the eukaryotic cell in a manner very similar to binary fission, supporting the endosymbiotic theory.

Question 3

Q: How do mitochondria produce the enzymes they need?
A: Mitochondria contain their own ribosomes to synthesize the enzymes they require.

Answer 3

A: Mitochondria contain their own ribosomes to synthesize the enzymes they require.

Question 4

Q: What is the structure of the mitochondrion, and why is it important?

Answer 4

A: The mitochondrion has two membranes (inner and outer). The inner membrane has many cristae (folds) to increase its surface area, as reactions occur on its inner-membrane-bound proteins.

Question 5

Q: What happens to pyruvate after glycolysis?

Answer 5

A: Following glycolysis, each pyruvate molecule enters a mitochondrion with the help of a transport protein, ultimately making its way into the matrix.

Question 6

Q: What happens to pyruvate inside the mitochondrion matrix?

Answer 6

A: While inside the matrix of the mitochondrion:

1. The carboxyl group is removed, producing CO2, which is waste.
2. During the removal of the carboxyl group (oxidation of COO-), NAD+ is reduced to NADH.

3.The remaining CH3CO group (acetyl) is bonded to Coenzyme A (CoA), forming Acetyl-CoA, which is ready for the next stage of cellular respiration.

Question 7

Q: What is the Citric Acid Cycle (CAC), and what does it do?

Answer 7

A: The Citric Acid Cycle (CAC), formerly known as the Krebs Cycle, is an 8-step pathway that completes the oxidation of glucose, which is currently in the form of two acetyl groups, each attached to a CoA.

Question 8

Q: How many trips through the Citric Acid Cycle (CAC) are required for one glucose molecule?

Answer 8

A: One glucose molecule requires two trips through the Citric Acid Cycle (CAC).

Question 9

What are the steps of the Citric Acid Cycle (CAC)?

Answer 9

1. Acetyl-CoA is hydrolyzed, and the acetyl group (C2) is bonded to oxaloacetate (C4), creating citrate (C6).
2. Citrate (C6) is isomerized to isocitrate (C6).
3. Isocitrate (C6) is oxidized to α-ketoglutarate (C5), removing CO2. NAD+ is reduced to NADH.
4. α-Ketoglutarate (C5) is oxidized, removing CO2. NAD+ is reduced to NADH. The resulting succinyl group (C4) is bonded to CoA, creating succinyl-CoA.
5. Succinyl-CoA is hydrolyzed into succinate (C4). GDP is phosphorylated into GTP, which is used to phosphorylate ADP → ATP.
6. Succinate (C4) is oxidized, removing 2H, turning it into fumarate (C4). FAD is reduced to FADH2.
7. A water molecule is added to fumarate (C4), producing malate (C4).
8. Malate (C4) is oxidized to oxaloacetate (C4). NAD+ is reduced to NADH.

By this point, glucose (C6H12O6) has been fully oxidized into 6 CO2.

Question 10

Q: How many ATP have been produced during the Citric Acid Cycle, and how were they made?

Answer 10

A: 6 ATP have been produced so far (with 2 used). These 6 ATP were made via substrate-level phosphorylation, which is the transfer of phosphate from one high-energy molecule to another.

Question 11

Q: Where are the other 34 ATP molecules produced in cellular respiration?

Answer 11

A: The other 34 ATP molecules are produced through the electron transport chain (ETC) and oxidative phosphorylation, where the reduced electron carriers NADH and FADH2 are used to generate ATP.

Question 12

Question 13

Q: What is the electron transport chain (ETC)?

Answer 13

A: The electron transport chain (ETC) is a system of components embedded in the mitochondrial inner membrane that uses electrons from NADH and FADH2 to generate ATP.

Question 14

What happens in the electron transport chain (ETC) step-by-step?

Answer 14

1. NADH is oxidized to NAD+ at Complex I, depositing 2 electrons (e-) at Complex I. This provides enough energy to pump 4 protons (H+) from the matrix into the intermembrane space.
2. Coenzyme Q (Q) carries the 2 electrons from Complex I to Complex III, providing enough energy to pump 4 more protons into the intermembrane space.
3. Cytochrome c (Cyt c) carries the 2 electrons from Complex III to Complex IV, providing enough energy to pump 2 more protons into the intermembrane space.
4. Every 4 electrons that arrive at Complex IV are combined with O2 and 4 protons in the matrix to make 2H2O. The intermembrane space now has a high concentration of protons (H+). The ATP synthase enzyme uses the energy produced by protons traveling down the concentration gradient to phosphorylate ATP.

Question 15

How does FADH2 contribute to the electron transport chain (ETC)?

Answer 15

A: FADH2 enters the ETC at Complex II, which does not pump any protons (H+). Coenzyme Q (Q) transports the 2 electrons from Complex II to Complex III, and cytochrome c (Cyt c) transports them to Complex IV. This results in a total of 6 protons being pumped into the intermembrane space from FADH2.

Question 16

Q: What is oxidative phosphorylation?

Answer 16

A: Oxidative phosphorylation is the production of ATP using electron transport to create an electrochemical gradient, followed by chemiosmosis across the mitochondrial inner membrane.

Question 17

How does ATP synthase function in ATP production?

Answer 17

A: ATP synthase acts like a turbine, facilitating the diffusion of H+ through the mitochondrial inner membrane. Every 4 H+ that move through it provide enough energy to phosphorylate 1 ATP.

Question 18

Q: How many ATP can be made from 1 NADH in the electron transport chain?

Answer 18

A: NADH provides enough energy to pump 10 H+ into the intermembrane space. Since each ADP requires 4 H+ to phosphorylate, approximately 3 ATP can be made from 1 NADH.

Question 19

Q: How many ATP can be made from 1 FADH2 in the electron transport chain?

Answer 19

A: FADH2 provides enough energy to pump 6 H+ into the intermembrane space. Since each ADP requires 4 H+ to phosphorylate, approximately 2 ATP can be made from 1 FADH2.

Question 20

Why is cellular respiration thermodynamically favored?

Answer 20

A: Cellular respiration is thermodynamically favored because:

1st Law of Thermodynamics: Energy is neither created nor destroyed; it is transformed from glucose into ATP and heat.
2nd Law of Thermodynamics: The entropy of the universe increases as energy is released in the form of heat and as complex molecules are broken into simpler ones.

Question 21

What are the three main purposes of oxidative phosphorylation in biology?

Answer 21

A: Oxidative phosphorylation serves three main purposes:

1. It is the primary method of ATP generation in aerobic organisms.
2. It recycles NAD+ and FAD, enabling glycolysis and the citric acid cycle to continue.
3. It consumes O2, reducing its potentially harmful effects at high concentrations.

Question 22

symptoms of oxygen toxicity

Answer 22

Question 23

Q: How does shivering help humans stay warm in colder temperatures?

Answer 23

A: Shivering generates heat through muscle contractions, which require ATP. This engages the cellular respiration pathway, producing heat as a byproduct.

Question 24

Q: What happens to the energy from cellular respiration that is not stored as chemical energy?

Answer 24

A: Not all of the energy from cellular respiration is captured and stored as chemical energy; some of it is released as heat.

Question 25

Q: What is non-shivering thermogenesis and how does it help in heat production?

Answer 25

A: Non-shivering thermogenesis is heat production that is not associated with muscle activity. It occurs in human infants and some animals, where specialized tissues, like brown adipose tissue, generate heat to maintain body temperature.

Question 26

Q: What is the role of uncoupling protein (UCP1) in brown adipose tissue?

Answer 26

A: Brown adipose tissue contains special mitochondria that express uncoupling protein (UCP1). This protein allows protons to leak across the mitochondrial inner membrane, uncoupling electron transport from ATP synthesis and generating heat instead of ATP.

Question 27

Q: How does UCP1 in brown adipose tissue generate heat?

Answer 27

A: UCP1 allows H+ in the intermembrane space to re-enter the mitochondrial matrix without generating ATP. Instead, the energy from this proton movement is released as heat, contributing to thermogenesis.