Q: A membrane protein is found to span the lipid bilayer with a single alpha helix. Approximately how many amino acids are required to span the membrane if the thickness of the hydrophobic core is 3 nm and the rise per residue in an alpha helix is 0.15 nm?

$$3 \text{ nm} \div 0.15 \text{ nm/residue} = 20$$ amino acids

Question 1

Which of the following changes would most likely increase the fluidity of a biological membrane at low temperature?

Accepted Answer

Increasing the proportion of unsaturated and shorter fatty acids in the membrane lipids

Question 2

A membrane protein is found to span the lipid bilayer with a single alpha helix. Approximately how many amino acids are required to span the membrane if the thickness of the hydrophobic core is 3 nm and the rise per residue in an alpha helix is 0.15 nm?

Accepted Answer

$$3 	ext{ nm} \div 0.15 	ext{ nm/residue} = 20$$ amino acids

Question 3

Which of the following best explains why phospholipids spontaneously form bilayers in aqueous solutions?

Accepted Answer

The hydrophobic effect drives the hydrophobic tails to avoid water, while the hydrophilic heads interact with water

Question 4

Integral membrane proteins can be removed from the membrane by which of the following treatments?

Accepted Answer

Mild detergent

Question 5

Which of the following statements about cholesterol's effect on membrane fluidity is correct?

Accepted Answer

At low temperatures, cholesterol disrupts close packing of fatty acids, increasing fluidity

Question 6

Which of the following best describes the difference between primary and secondary active transport?

Accepted Answer

Primary active transport uses ATP hydrolysis directly, while secondary active transport uses the energy stored in an ion gradient

Question 7

A transporter moves glucose into a cell using the energy stored in a sodium ion gradient. This is an example of:

Accepted Answer

Secondary active transport

Question 8

Which of the following equations correctly represents the free energy change for the movement of an ion across a membrane?

Accepted Answer

$$\Delta G = RT \ln \left( \frac{C_2$}{C_1$} \right) + zF\Delta V$$

Question 9

Which of the following is a function of membrane proteins?

Accepted Answer

Detecting signals from outside the cell

Question 10

Why do different cellular membranes (e.g., plasma membrane vs. mitochondrial membrane) have different lipid and protein compositions?

Accepted Answer

Because each membrane must perform unique functions requiring specific lipids and proteins

Question 11

Which of the following best describes the role of flippases in biological membranes?

Accepted Answer

They catalyze the movement of lipids from one leaflet of the bilayer to the other

Question 12

A mutation causes a membrane protein to lose all hydrophobic amino acids in its transmembrane domain. What is the most likely consequence?

Accepted Answer

The protein will be unable to insert into the membrane

Question 13

Which of the following is a reason why simple diffusion of polar compounds across a membrane is slow?

Accepted Answer

Polar compounds are repelled by the hydrophobic interior of the membrane

Question 14

Which of the following best explains why only transmembrane proteins with long hydrophobic chains are found in lipid rafts?

Accepted Answer

Lipid rafts are enriched in saturated fatty acids and cholesterol, which favor the inclusion of proteins with long hydrophobic domains

Question 15

Which of the following is a characteristic of facilitated diffusion?

Accepted Answer

It moves substances down their concentration gradient with the help of a protein

Question 16

Which of the following best describes the function of ABC transporters?

Accepted Answer

They use ATP hydrolysis to transport a wide variety of substrates across membranes

Question 17

A voltage-gated potassium channel opens in response to which of the following?

Accepted Answer

A change in membrane potential

Question 18

Which of the following is a plausible reason why many anti-tumor drugs are exported by multidrug transporters?

Accepted Answer

Multidrug transporters have broad substrate specificity and can pump out many hydrophobic compounds, including drugs

Question 19

Which of the following best explains why the sodium-potassium ATPase is important for animal cells?

Accepted Answer

It maintains the electrochemical gradients of sodium and potassium across the plasma membrane

Exam 4- chap 11 Membrane

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