Q1. Tetramethylrhodamine (TMR) is a positively-charged fluorescent dye that easi

Question

Q1.

Tetramethylrhodamine (TMR) is a positively-charged fluorescent dye that easily crosses lipid membranes. It specifically labels mitochondria in living cells, but it does not label the mitochondria of dead cells. The difference in labeling is directly due to: Select ONE option:

A. differences in the reduction of complex I in the ETC.

B. the loss of the pH gradient across the inner mitochondrial membrane.

C. differences in the levels of ATP between the two cells.

D. differences in the levels of pyruvate between the two cells.

Q2.

What would happen to the (i) magnitude of the mitochondrial proton gradient, (ii) rate of mitochondrial oxygen consumption, and (iii) rate of acetyl-CoA oxidation in cells treated with the ATP synthase inhibitor oligomycin? Select ONE option:

A. (i) increase, (ii) increase, (iii) increase

B. (i) increase, (ii)decrease, (iii) increase

C. (i) decrease, (ii)decrease, (iii) decrease

D. (i) decrease, (ii)increase, (iii) increase

E. (i) increase, (ii) decrease, (iii) decrease

Q3.

Where might you expect to find mutations that lead to mitochondrial disease (i.e., diseases that are a consequence of mitochondrial dysfunction)? Select ONE option:

A. Nuclear DNA

B. Mitochondrial DNA

C. Both

Q4.

Which of these tissues are most likely to display significant defects in patients with a mitochondrial disease?

(Select all that apply.)

A. Cartilage

B. Heart

C. Bone

D. Neural

E. Adipose

Q5.

Barth Syndrome is characterized by dysfunctional mitochondria with a lower capacity to produce ATP. Barth syndrome patients experience difficulty walking and exercising. Why do Barth patients have these impairments?

(Select all that apply.)

A. Because ATP is required for skeletal muscle contraction.

B. Because ATP is required for the pumping of blood by the heart.

C. Because ATP is required for the release of oxygen by red blood cells.

D. Because ATP is required for absorbing oxygen by red blood cells.

Q6.

Bongkrekic acid is a mitochondrial toxin produced by bacteria in fermented coconuts. It blocks the inner membrane protein responsible for transporting ATP from the mitochondrial matrix to the cytosol. Bongkrekic acid also inhibits ADP import from the cytosol into the matrix for phosphorylation. Which of the following will occur in a cell exposed to bongkrekic acid?

(Select all that apply.)

A. Most ATP in the cell will be produced by glycolysis because the mitochondria are inhibited.

B. The mitochondrial membrane potential will decrease due to decreased ETC proton pumping.

C. Respiration will decrease because the ATP synthase will lack ADP as the reactant.

D. Mitochondrial ATP levels will decrease.

Q7.

Experiment 1. Two sets of cells are subjected to a FRAP experiment. One cell has a lipid bilayer that includes cholesterol, which makes it less fluid; and the other cell has a membrane made purely of phospholipids. The results are shown below. Which curve, A or B, was obtained from cells with a membrane that includes cholesterol?

Select ONE option:

1. A

2. B

Experiment 2. Membrane fluidity decreases as the temperature cools. If you conducted two FRAP experiments with the same cell, one experiment at warm temperature, and the other at a cooler temperature, which of the FRAP curves below best represents the cell at the warmer temperature?

Select ONE option:

1. A

2. B

Q8.

Transport along a microtubule is especially important in delivering mitochondria from the cell body of a motor neuron to the end of an axon, where there is a high energy demand for neurotransmission. Miro is an adaptor protein that binds mitochondria to the motor proteins responsible for carrying mitochondria along microtubules.

Part 1. What symptom(s) would you expect to see in a patient carrying a deletion to the miro gene?

(Select ALL that apply.)

A. Difficulty walking because the sciatic nerve, which is the longest cell in the body, will be impaired.

B. Vision loss due to impairment of short retinal neurons

C. Deficiencies in neurons across entire nervous system, regardless of size.

Part 2. Disrupting which of the following processes would result in similar symptoms?

(Select ALL that apply.)

A. Microtubule organization

B. Motor protein interaction with microtubules

C. Actin filament oligomerization

Q9.

The two organelles that are responsible for post-translational modifications of proteins are the ------------ and the --------------

Select ONE option for the FIRST blank:

A. Nucleus

B. Smooth ER

C. Rough ER

D. Lysosome

Select ONE option for the SECOND blank:

A. Nucleus

B. Smooth ER

C. Rough ER

D. Lysosome

Q10.

Mitochondrial fission is important for healthy mitochondrial function. Mitochondrial fission allows for old, defective components from one mitochondrion to be replaced with new ones. Mitochondrial fission facilitates this replacement of old mitochondrial parts by isolating them in small membrane-bound vesicles that are then degraded by the cell.

What is the expected consequence for mitochondrial energy production in a pathological condition where mitochondrial fission is reduced?

Select ONE option:

A. The rate of mitochondrial replacement will increase and ATP levels will increase.

B. The rate of mitochondrial replacement will decrease and ATP levels will decrease.

Explanation / Answer

1. Tetramethylrhodamine (TMR) is a red-orange, cationic, or positively charged dye. It is used for the analysis of the change in membrane potential of mitochondria, in live and dead cells, by using flow cytometry, spectrophotometry or fluorescent microscopy techniques.

The mechanism of oxidative phosphorylation occurs in mitochondria of live cells. Electrons are transported across various components of electron transport chain (ETC), resulting in series of oxidation-reduction reactions within the membrane bound complexes in mitochondria (complex I, II, II, IV). Complex I, aids in pumping of proton in the intramembranous mitochondrial space. This creates an electrochemical gradient across mitochondrial membrane and a relative negative charge is created. Thus, TMR, being positively charges has affinity towards mitochondria of live cells.

Hence, Correct option is A

2. ATP synthase complex, designated as F0F1- ATP synthase, is located within the mitochondrial cristae. They help in back flow of proton, creating free energy to generate ATP. ATP synthase is composed of two parts: a) Coupling factor 1 (F1)- which contains the catalytic subunit of ATP synthase. b) Coupling factor 0 (F0) – which act as a proton channel between mitochondrial matrix and intramembranous mitochondrial space. Oligomycin binds to F0 part and inhibit actions of ATP synthase. This results in decrease in cellular respiration.

Hence, Correct option is C

3. Mitochondrial diseases or disorders may be caused by mutations of genes located in mitochondrial DNA. They may also be caused due to mutation of genes that codes mitochondrial components but are located on nuclear DNA.

Hence, Correct option is C

4. Mitochondria are important for producing about 90% of energy required by cellular functions. Thus, mitochondrial disorders will affect those cells more vitally, which requires lots of energy. Almost mitochondrial diseases affect all cells, except those lacking mitochondria (like RBC). But, most affected tissues are those of muscles, heart, and brain.

Hence, Correct options are B and D.

5. Barth syndrome is a X-linked mitochondrial disorder, leading to cardiomyopathy, neutropenia or cardioskeletal myopathy. This causes the heart muscles to become weak, and they are unable to pump blood.

Hence, Correct option is B.

6. Bongkrekic acid (BA) acts as mitochondrial inhibitor by inhibiting adenine nucleotide translocase (ANT) ad not ETC.

Hence, Correct option are C and D.

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