Chapter 14 - Energy Conversion

Question 1

What is the outer mitochondrial membrane, and what is its primary function?

Answer 1

It contains porins that allow molecules <5000 Da to pass freely, enabling exchange with the cytoplasm.

Question 2

Describe the function and structure of the inner mitochondrial membrane.

Answer 2

It is highly impermeable, hosts the electron transport chain (ETC), and folds into cristae to increase surface area for ATP production.

Question 3

How does the double membrane structure of mitochondria support its functions?

Answer 3

The outer membrane regulates metabolite passage, while the inner membrane facilitates ATP synthesis via the ETC and maintains a proton gradient.

Question 4

What are cristae, and why are they essential in mitochondria?

Answer 4

Cristae are folds in the inner membrane that increase surface area for ETC proteins, enhancing ATP production efficiency.

Question 5

What is cardiolipin, and what is its role in the inner mitochondrial membrane?

Answer 5

A unique phospholipid that stabilizes ETC complexes, supports cristae structure, and optimizes oxidative phosphorylation.

Question 6

Where does the TCA cycle take place, and what does it produce?

Answer 6

It occurs in the mitochondrial matrix, producing NADH, FADH₂, and GTP from acetyl-CoA oxidation.

Question 7

What is the function of acetyl-CoA in the TCA cycle?

Answer 7

It enters the TCA cycle, where it is fully oxidized to CO₂, yielding electron carriers NADH and FADH₂ for the ETC.

Question 8

What role do NADH and FADH₂ play in mitochondrial function?

Answer 8

These electron carriers transfer electrons to the ETC, fueling ATP production through oxidative phosphorylation.

Question 9

How does the TCA cycle integrate with other metabolic pathways?

Answer 9

It links with glycolysis, fatty acid oxidation, and amino acid catabolism, centralizing cellular energy metabolism.

Question 10

Describe the structure of NADH and its role in the ETC.

Answer 10

NADH is a derivative of niacin (Vitamin B3) that donates electrons to Complex I, initiating the ETC and proton pumping.

Question 11

What is FADH₂, and how does it function in the ETC?

Answer 11

FADH₂ is derived from riboflavin (Vitamin B2) and donates electrons at Complex II, indirectly contributing to proton pumping.

Question 12

What is the role of Complex I in the ETC?

Answer 12

It oxidizes NADH, transfers electrons to CoQ, and pumps 4 H⁺ into the intermembrane space.

Question 13

Describe the function of Complex II in the ETC.

Answer 13

It oxidizes FADH₂ and transfers electrons to CoQ but does not pump protons, contributing fewer ATP per molecule.

Question 14

What is the function of Complex III in the ETC?

Answer 14

Complex III receives electrons from CoQ and pumps 4 H⁺ via the Q cycle, transferring electrons to cytochrome c.

Question 15

How does Complex IV contribute to ATP synthesis?

Answer 15

It transfers electrons from cytochrome c to O₂, forming H₂O, and pumps 2 H⁺ per electron pair, completing the ETC.

Question 16

What is ubiquinone (CoQ), and what is its role in the ETC?

Answer 16

CoQ is a lipid-soluble electron carrier that shuttles electrons between Complexes I/II and III within the inner membrane.

Question 17

Explain the role of cytochrome c in the ETC.

Answer 17

It is a mobile protein that transfers electrons from Complex III to Complex IV, essential for continuing the electron flow.

Question 18

Why is oxygen essential for the ETC?

Answer 18

Oxygen is the final electron acceptor in Complex IV, forming H₂O and allowing continued electron transport and ATP production.

Question 19

What is chemiosmosis, and how does it contribute to ATP synthesis?

Answer 19

Chemiosmosis is the movement of protons across the inner membrane, driven by the ETC, which ATP synthase uses to produce ATP.

Question 20

Describe the structure and function of ATP synthase.

Answer 20

ATP synthase has F₀ (proton channel) and F₁ (ATP-producing) units; proton flow through F₀ drives rotation, catalyzing ATP synthesis in F₁.

Question 21

How does the H⁺ gradient across the inner mitochondrial membrane drive ATP synthesis?

Answer 21

The proton gradient created by the ETC provides potential energy that ATP synthase harnesses to convert ADP and Pi into ATP.

Question 22

Explain the rotational mechanism of ATP synthase.

Answer 22

Proton flow through F₀ rotates the complex, changing F₁’s conformation, sequentially binding ADP and Pi, synthesizing ATP, and releasing it.

Question 23

What are the main features of the mitochondrial genome?

Answer 23

It is circular, ~16.5 kb, encodes 13 proteins for oxidative phosphorylation, and has a higher mutation rate than nuclear DNA.

Question 24

Describe the process of maternal inheritance in mitochondria.

Answer 24

Mitochondrial DNA is inherited exclusively from the mother due to selective degradation of paternal mitochondria in the zygote.

Question 25

How does heteroplasmy affect mitochondrial diseases?

Answer 25

Variability in mutated vs. normal mtDNA within cells (heteroplasmy) affects the severity and expression of mitochondrial diseases.

Question 26

What is mitochondrial biogenesis?

Answer 26

The growth and division of mitochondria, involving replication, transcription, and translation of mitochondrial DNA.

Question 27

How are nuclear-encoded mitochondrial proteins imported into mitochondria?

Answer 27

Proteins are synthesized in the cytosol and imported via TOM and TIM complexes, directed by specific targeting signals.

Question 28

What role do the TOM and TIM complexes play in protein import?

Answer 28

TOM transports proteins across the outer membrane, and TIM moves them across the inner membrane or to their specific mitochondrial compartment.

Question 29

Explain the significance of targeting signals in mitochondrial protein import.

Answer 29

Targeting signals direct proteins to mitochondria, where they are recognized by import machinery, ensuring proper localization.

Question 30

How does electron leakage in the ETC lead to ROS formation?

Answer 30

Electrons can escape from ETC complexes, especially Complex I and III, forming reactive oxygen species like superoxide.

Question 31

What are superoxide dismutase (SOD) and catalase?

Answer 31

Enzymes that neutralize ROS; SOD converts superoxide to hydrogen peroxide, and catalase converts hydrogen peroxide to water and oxygen.

Question 32

How does mitochondrial DNA damage contribute to aging?

Answer 32

Accumulation of mutations in mtDNA from ROS exposure leads to mitochondrial dysfunction, which is associated with aging.

Question 33

What are uncouplers, and how do they affect ATP production?

Answer 33

Uncouplers, like DNP, disrupt the proton gradient by allowing protons to leak, causing energy to be released as heat rather than used for ATP synthesis.

Question 34

How does thermogenin (UCP1) function in brown fat?

Answer 34

UCP1 acts as a natural uncoupler in brown fat, allowing proton leakage for heat generation instead of ATP production, useful in cold environments.

Question 35

Name some poisons that inhibit the ETC and their effects.

Answer 35

Rotenone blocks Complex I, cyanide inhibits Complex IV, and oligomycin blocks ATP synthase; all inhibit ATP production, leading to cell death.

Question 36

How does cyanide inhibit the ETC?

Answer 36

Cyanide binds to cytochrome c oxidase (Complex IV), preventing electron transfer to oxygen, halting ATP synthesis and causing cellular hypoxia.

Question 37

What effect does oligomycin have on ATP synthase?

Answer 37

Oligomycin binds the F₀ unit, blocking proton flow and stopping ATP production, effectively halting cellular respiration.

Question 38

Describe the role of 2,4-dinitrophenol (DNP) as an uncoupler.

Answer 38

DNP allows protons to bypass ATP synthase, dissipating the proton gradient and increasing metabolic rate, with dangerous heat as a byproduct.

Question 39

What is the mechanism of action for carbon monoxide in ETC inhibition?

Answer 39

Carbon monoxide binds to Complex IV, preventing electron transfer