Q1. Phospholipids in a bilayer can move in some directions easily, while they mo

Question

Q1.

Phospholipids in a bilayer can move in some directions easily, while they move in other directions only very rarely.

Determine which type(s) of phospholipid movement are LEAST likely to happen within a bilayer:

(Select all that apply.)

A. Lateral diffusion

B. Rotation

C. Flip-flop

Q2. Write the correct order of FRAP experiments:

1. Wait

2. Shine an intense laser at a specific region of a membrane

3. Observe fading of the photobleaching

4. Observe photobleaching of the membrane

5. Add fluroscent label to the phospholipid bilayer

Q3. 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.

Q4. Which of the following is a characteristic of eukaryotes but NOT of prokaryotes?

A. The cell is surrounded by a plasma membrane that is a phospholipid bilayer.

B. DNA serves as the genetic material

C. The genetic material is surrounded by its own phospholipid bilayer, distinct from the phospholipid bilayer that surrounds the cell.

D. Organisms can be single-celled

Q5.

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

Explanation / Answer

1. C. Flip-flop (Studies show that flip flop movement is rare, once a month in the sample. One of the main reason is energy requirement is more.)

2. Add fluroscent label to the phospholipid bilayer > Shine an intense laser at a specific region of a membrane > Observe photobleaching of the membrane > Wait > Observe fading of the photobleaching.

5>2>4>1>3

This experiment is performed to observe the movement of proteins in phospholipid bilayer.

3. B. The membrane stays dark after photobleaching , meaning that the labeled phospholipids diffuse into the bleached region. (The labelled proteins move by lateral diffusion to the bleached part and lose its colour.)

4. C. The genetic material is surrounded by its own phospholipid bilayer, distinct from the phospholipid bilayer that surrounds the cell. (This is false as Prokaryotes don't have any membrane for genetic material.)

5.

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, Cytoplasm. As the enzyme 2 is more active in pH range of 7-8 and cytoplasm i.e region A has pH 7.

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

2. B, Nucleus. As the enzyme 1 is more active in pH range of 2-3 and nucleus i.e region B has pH 2.

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

2. NO, Prokaryotes dont have separate nucleus the genetic material is present in the cytoplasm itself. The pH of cytoplasm of Prokaryotes is around 7.2 - 7.8 and hence only enzyme 2 will have full activity.

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