Module 5: Aerobic Respiration and Mitochondria

Question 1

What do anaerobes do?

Answer 1

They capture and utilize energy by oxygen-independent
metabolism like glycolysis and fermentation.

Question 2

What do aerobes do?

Answer 2

They use oxygen to extract more energy from organic
molecules

Question 3

In eukaryotes where does the utilization of oxygen as a means of energy take place?

Answer 3

Mitochondria.

Question 4

What is mitochondrial fusion?

Answer 4

Mitochondria fusing with one another.

Question 5

What is mitochondrial fission?

Answer 5

Mitochondria splitting into two.

Question 6

How is mitochondrial fission induced?

Answer 6

By contact with thin tubules from the Endoplasmic reticulum (ER), which can encircle the mitochondrion like a noose.

• The ER tubules initiate constriction, which is then completed through the action
  of soluble proteins that are recruited to the outer surface of the mitochondrion
  from the cytosol.

Question 7

What are often associated with fatty acid-containing oil droplets from which they derive raw materials for ATP production?

Answer 7

Mitochondria are often associated with fatty acid-containing oil droplets from which they derive raw materials to be oxidized in order to make ATP.

Question 8

Besides ATP production, what other functions are associated with mitochondria?

Answer 8

Mitochondria are also the sites of synthesis of numerous substances, including certain amino acids and heme groups.

Question 9

How do mitochondria contribute to cellular activities?

Answer 9

Mitochondria play a vital role in the uptake and release of calcium ions, which are essential triggers for cellular activities.

Question 10

What role do mitochondria play in regulating cellular events?

Answer 10

Mitochondria regulate events involved in cell death, which plays an enormous role in the life of all multicellular animals.

Question 11

What are the two major domains of the inner mitochondrial membrane?

Answer 11

The two major domains of the inner mitochondrial membrane are the inner boundary membrane domain and the outer domain.

Question 12

What is the role of the inner boundary membrane domain in mitochondria?

Answer 12

The inner boundary membrane domain is rich in proteins responsible for the import of mitochondrial proteins.

Question 13

What is found in the outer domain of the inner mitochondrial membrane?

Answer 13

The outer domain of the inner mitochondrial membrane consists of invaginated membranous sheets called cristae.

Question 14

What is the function of the outer mitochondrial membrane?

Answer 14

The outer mitochondrial membrane serves as an outer boundary for the mitochondrion.

Question 15

What is the primary function of the cristae in mitochondria?

Answer 15

The cristae house the machinery needed for aerobic respiration and ATP formation.

Question 16

How is the mitochondrion divided into different aqueous compartments?

Answer 16

The mitochondrion is divided into two aqueous compartments: the Matrix, which is within the interior of the mitochondrion, and the Intermembrane space, which is located between the outer and inner mitochondrial membranes.

Question 17

What does the mitochondrial matrix contain?

Answer 17

The mitochondrial matrix contains ribosomes, circular DNA for manufacturing its own RNAs and proteins, and mitochondrial DNA (mtDNA), which encodes 12 proteins, 12S & 16S rRNAs, and 22 tRNAs.

Question 18

What is the significance of mitochondrial DNA (mtDNA)?

Answer 18

Mitochondrial DNA (mtDNA) is thought to be the legacy from a single aerobic bacterium and is a relic found in all eukaryotic cells. It encodes essential proteins for the inner mitochondrial membrane.

Question 19

What is ATP, and what is its role in the cell?

Answer 19

ATP (adenosine triphosphate) is the energy currency of the cell. It is composed of adenine, ribose, and three phosphate groups. ATP releases energy through dephosphorylation, becoming ADP (adenosine diphosphate), and is used to perform cellular work.

Question 20

What is the function of electron carriers in cellular pathways?

Answer 20

Electron carriers bind and transport high-energy electrons between compounds in metabolic pathways. Examples of electron carriers include Nicotinamide adenine dinucleotide (NAD) and Flavin adenine dinucleotide (FAD+). NAD+ is the oxidized form, while NADH is the reduced form, and these molecules play roles in oxidation and reduction reactions within cells.

Question 21

What is glycolysis, and where does it occur?

Answer 21

Glycolysis is the first pathway used in the breakdown of glucose to extract energy, and it occurs in the cytosol of the cell.

Question 22

How does glycolysis split a six-carbon glucose molecule?

Answer 22

Glycolysis splits a six-carbon glucose molecule into two three-carbon sugars, known as pyruvate.

Question 23

What is the net gain of ATP molecules produced during glycolysis?

Answer 23

Glycolysis requires the investment of two ATP molecules in the first half but produces four ATP molecules during the second half, resulting in a net gain of two ATP molecules per molecule of glucose for the cell.

Question 24

What is fermentation, and when does it occur?

Answer 24

Fermentation is an anaerobic process that regenerates NAD+ from glucose. It occurs in the cytosol and is employed in situations where there is insufficient oxygen supply, such as in muscle cells.

Question 25

What is the first step in oxidative metabolism, and where does it take place?

Answer 25

The first step in oxidative metabolism is glycolysis, which occurs in the cytoplasm (cytosol) of the cell.

Question 26

What is the TCA cycle, and what is its role in aerobic respiration?

Answer 26

The Tricarboxylic Acid (TCA) cycle, also known as the Krebs or citric acid cycle, is a crucial part of aerobic respiration. It harnesses the chemical energy of acetyl coenzyme A (acetyl CoA) into reducing power in the form of nicotinamide adenine dinucleotide (NADH). It involves the oxidation of acetyl groups and the regeneration of oxaloacetate.

Question 27

How are high-energy electrons generated during the TCA cycle utilized?

Answer 27

High-energy electrons generated during the TCA cycle are transferred to electron carriers such as NADH and FADH2. These carriers then pass the electrons through the mitochondrial electron transport chain to ultimately produce ATP.

Question 28

How is ATP formed in mitochondria through oxidative phosphorylation?

Answer 28

ATP formation in mitochondria through oxidative phosphorylation involves the controlled movement of protons (H+) across the inner mitochondrial membrane. The energy released as electrons are passed through the electron transport chain is used to pump protons into the intermembrane space. The movement of protons back into the mitochondrial matrix through ATP synthase is coupled with the synthesis of ATP, a process known as chemiosmosis.

Question 29

What is the role of reduced coenzymes like NADH and FADH2 in ATP formation?

Answer 29

Reduced coenzymes like NADH and FADH2 carry high-energy electrons that are used in the electron transport chain to generate ATP. These electrons are transferred through a series of electron carriers to create an electrochemical gradient, which is used to synthesize ATP.

Question 30

How does the glycerol phosphate shuttle transfer electrons into the intermembrane space?

Answer 30

The glycerol phosphate shuttle transfers electrons from cytosolic NADH to dihydroxyacetone phosphate (DHAP), forming glycerol-3P. Glycerol-3P then shuttles the electrons into the intermembrane space, where glycerol-3-phosphate dehydrogenase (GSPDH) transfers them to FAD, making FADH2. This process helps move electrons to the electron transport chain for ATP generation.

Question 31

What is the final step of the Electron Transport Chain (ETC) in mitochondria?

Answer 31

The final step of the ETC is the successive transfer of electrons from reduced cytochrome c to oxygen.

Question 32

What complex catalyzes the reduction of oxygen (O2) in the ETC, and what is its role?

Answer 32

Complex IV, also known as cytochrome oxidase, catalyzes the reduction of oxygen (O2) in the ETC. It acts as a redox-driven proton pump, contributing to the establishment of the proton-motive force.

Question 33

How many protons are consumed and translocated when one molecule of O2 is reduced in the ETC?

Answer 33

When one molecule of O2 is reduced in the ETC, 8 protons are involved in the process. Four protons are consumed to form two molecules of water, and four protons are translocated to the intermembrane space.

Question 34

What are the two components of the proton gradient that contribute to the proton-motive force?

Answer 34

The two components of the proton gradient that contribute to the proton-motive force are the concentration gradient between the matrix and intermembrane space (creating a pH gradient) and the separation of charge across the membrane (creating an electric potential or voltage).

Question 35

What is the role of the proton-motive force (Δp) in mitochondria?

Answer 35

The proton-motive force (Δp) in mitochondria is responsible for various processes, including ATP synthesis. It is also involved in driving the uptake of ADP and Pi into the mitochondria in exchange for ATP and H+ ions, respectively.

Question 36

What is the structure of ATP synthase, and what are its subunits?

Answer 36

ATP synthase consists of two main components: the F1 particle, which is the catalytic subunit containing three catalytic sites for ATP synthesis, and the F0 particle, which attaches to the F1 and is embedded in the inner mitochondrial membrane. The base of ATP synthase contains a channel through which protons are conducted.

Question 37

What are the other roles of the proton-motive force besides ATP synthesis?

Answer 37

Besides ATP synthesis, the proton-motive force in mitochondria is involved in driving the uptake of ADP and Pi, as well as facilitating the transport of calcium ions into the mitochondrion. It is also important for mitochondrial fusion and other energy-requiring processes.

Question 38

How is the proton-motive force visualized, and what dye is used for this purpose?

Answer 38

The proton-motive force can be visualized using a fluorescent dye called JC-1, which exhibits a color change from green to orange in response to changes in membrane potential, allowing researchers to visualize the force.

Question 39

Learning Objective 1:
Describe the origin, structure, and functions of the membranes and matrix of the mitochondrion.

Answer 39

The mitochondrion is an organelle with a double membrane structure. The outer mitochondrial membrane acts as the outer boundary, while the inner mitochondrial membrane is folded into structures called cristae. These cristae provide a large surface area for aerobic respiration and ATP formation. Within the mitochondrion, there are two aqueous compartments: the Matrix (located in the interior) and the Intermembrane space (between the outer and inner membrane). The matrix contains ribosomes, circular DNA, and various enzymes for metabolic processes, while the inner membrane houses the electron transport chain and ATP synthase.

Question 40

Learning Objective 2:
Outline the function of glycolysis, fermentation, the TCA cycle, and oxidative phosphorylation.

Answer 40

Glycolysis is the initial step in glucose metabolism that occurs in the cytosol. It breaks down glucose into two three-carbon pyruvate molecules and produces a net gain of two ATP molecules per glucose molecule.
Fermentation is an anaerobic process that regenerates NAD+ from glucose. It happens in the cytosol and is used when there’s insufficient oxygen. In muscle cells, fermentation can lead to the formation of lactate.
The TCA cycle (Tricarboxylic Acid Cycle) is a key component of aerobic respiration, occurring in the mitochondrial matrix. It generates NADH, FADH2, and ATP by oxidizing acetyl CoA derived from glucose or other substrates.
Oxidative phosphorylation is the process of ATP formation using the proton-motive force generated by the electron transport chain. High-energy electrons from NADH and FADH2 are transferred through a series of protein complexes, driving proton translocation across the inner mitochondrial membrane. The energy from proton flow back into the matrix via ATP synthase is used to synthesize ATP.

Question 41

Learning Objective 3:

Explain how the transport of electrons down the respiratory chain leads to the formation of a proton gradient.

Answer 41

The transport of electrons down the respiratory chain involves several protein complexes embedded in the inner mitochondrial membrane. As electrons move through these complexes, they lose energy. This energy loss is coupled with the active transport of protons (H+ ions) from the matrix to the intermembrane space. The movement of protons against their concentration gradient establishes a proton gradient. This proton gradient includes a pH gradient (ΔpH) due to differences in proton concentrations and an electric potential (Ψ) across the membrane. The combined proton gradient is referred to as the proton-motive force (Δp), and it represents stored energy that can be used for ATP synthesis.

Question 42

Learning Objective 4:

Explain how translocation of protons can establish a proton-motive force.

Answer 42

The translocation of protons (H+ ions) from the mitochondrial matrix to the intermembrane space during electron transport establishes a proton-motive force (Δp). This force results from two components:

1. Concentration Gradient (ΔpH): Protons are actively pumped against their concentration gradient, creating a difference in proton concentration (pH gradient) between the matrix and intermembrane space. This creates potential energy.
2. Electric Potential (Ψ): Simultaneously, the movement of positively charged protons generates an electric potential (voltage) across the inner mitochondrial membrane. This also contributes to potential energy.