Q1 . The data from FRAP experiments provide experimental support for membrane fl

Question

Q1. The data from FRAP experiments provide experimental support for membrane fluidity. Why?Select ONE option:

A. The membrane stays dark after photobleaching, meaning that the unlabeled phospholipids diffuse into the bleached region.

B. The membrane stays dark after photobleaching , meaning that the labeled phospholipids diffuse into the bleached region.

C. The membrane recovers its fluorescence after photobleaching, meaning that the labeled phospholipids diffuse into the bleached region.

D. The membrane recovers its fluorescence after photobleaching,meaning that the unlabeled phospholipids diffuse into the bleached region.

Q2.

Consider the simplified schematic of a eukaryotic cell shown below.

Region A indicates the cell’s cytoplasm; Region B indicates the inside of an organelle. The pH of the cytoplasm is 7, and the pH of organelle B is 2. (“pH” is a measure of the acidity of a solution.)

The optimum pH range for each enzyme is shown below. Consider the activity of two enzymes, enzyme 1 and enzyme 2 (an enzyme is a protein that enables chemical reactions to proceed more quickly).

Part 1. In which region of the cell (A or B) will the purple enzyme (enzyme 2, right-most curve) be most active?

1. A

2. B

Part 2. In which region (A or B) will the blue enzyme (enzyme 1, left-most curve) be most active?

1. A

2. B

Part 3. Imagine if both enzymes were present in the same prokaryotic cell. Could both enzymes have full activity?

1. YES

2. NO

Q3.

Eukaryotic cells tend to be 10-1,000 times larger than prokaryotic cells, which it means that it takes much longer for molecules to diffuse from one side of the cell to the other (just as getting across a large warehouse takes longer than getting across a small room). However, biological processes happen just as quickly in eukaryotic cells as they do in prokaryotic cells.

PART 1. From the choices below, which reason best explains why biological processes in eukaryotic cells happen just as quickly as in prokaryotic cells, despite being so much larger? Select ONE option:

A. The reactants and enzymes required for a particular biological process are concentrated in a particular organelle

B. The reactants and enzymes required for a particular biological process are distributed randomly throughout the eukaryotic cell

PART 2.  If we remove a process that occurs in an organelle and have that biological process happen in the cytoplasm of a eukaryotic cell instead, would you predict it would occur: Select ONE option:

A. Faster

B. Slower

C. At the same speed

Q4.

The wear and tear of daily cellular activity requires continuous replacement of aged dysfunctional proteins with newly synthesized proteins. These two processes are essential for maintaining cellular function and maximizing the lifespan of the cell. Protein synthesis occurs more efficiently in neutral pH while protein degradation occurs more efficiently in acidic pH.

Which cells provide the best conditions to carry out both processes?

Select ONE option:

A. Prokaryotes, because they can only have one compartment with a neutral pH.

B. Eukaryotes, because they have specialised membrane-bound organelles with acidic pH.

C. Prokaryotes, because they can live in an acidic environment.

D. Eukaryotes, because they have only one compartment that alternates between neutral and acidic pH.

Explanation / Answer

Q.1. Option C: The membrane recovers its fluorescence after photobleaching, meaning that the labeled phospholipids diffuse into the bleached region.

FRAP stands for Fluorescence Recovery After Photobleaching. During FRAP experiment, Lipid bilayer membrane is photolabelled by fluorophores. The property of fluorophore is that they absorb light of a particular wavelength and emits light of higher wavelength. During the experiment, a light of very high intensity is flashed on a fixed spot of the membrane, which leads to loss of the ability of fluorophore to emit light.This results in a dark spot in the membrane. Rest of the membrane is labelled with fully functional fluorophores. As the Brownian motion sets in, the functional fluorophores diffuse in the dark spot and after sometime, the dark spot vanishes. If the membrane had been non-fluid, the dark spot would have been intact. Fading of the spot proves the membrane fluidity. Photo bleached spot doesnot diffuse into normal area because the spot has been fixed already rendering it non-diffusible.

References:

Q.2.      Part1. 1 (Enzyme will be most active in the cytoplasm of the cell denoted by ‘A’)

Explanation: Clear from the graph shown here the % activity of the enzyme 2 is highest in the environment where pH is near 7(neutral) and in highly acidic (pH<7) or highly basic (ph>7) environment it’s activity diminishes.

            Part2. 2 (Enzyme will be most active in the organelle of the cell denoted by ‘B’)

Explanation: Clear from the graph shown here the percentage activity of the enzyme 1 is highest in the environment where pH is two (acidic), as the pH increases the activity starts reducing, and goes to near zero.

            Part3. 2 (No, Both Enzymes can’t have the full activity in the same prokaryotic cell)

Explanation: Both enzyme cannot have full functionality in a prokaryotic cell because the prokaryotic cells do not possess any organelle and thus have one uniform environment. Both the enzyme given here have properties suitable to two completely different environment. This is the reason why only one of them will be functional in any given environment (pH=2 or pH=7). Although both the enzymes will be inactive at pH>7(basic)

Q.3.      Part 1. Option A (The reactants and enzymes required for a particular biological process are concentrated in a particular organelle).

Explanation: One of the most characteristic feature of eukaryotic cell is division of labor and it provides the ability to handle each task very efficiently. Different tasks are handled by different specialized organelle. Reactants and enzymes are concentrated in different organelle and enables cells to perform quick reactions.

Reference: https://www.nature.com/scitable/topicpage/eukaryotic-cells-14023963

Part 2. B. Slower.

Explanation: The increased volume of the eukaryotic cells will definitely reduce the concentration and will cause slow reactions. Large size will make it more time consuming for the molecules to come together and slow the reaction. Generally, a cell enters in a cell division phase when it reaches a certain size and the reaction starts getting affected.

Q.3. B. Eukaryotes, because they have specialized membrane-bound organelles with acidic pH.

Explanation: Eukaryotic cells have lysosomes, a specialized compartment that has very low pH and helps in protein degradation. While protein synthesis happens in Endoplasmic Reticulum with the help of Ribosomes. Prokaryotes do not have such abilities and thus are less efficient as compared to eukaryotic cells when comes to many cell associated functions.

Refence: Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. Protein Degradation. https://www.ncbi.nlm.nih.gov/books/NBK9957/

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