Question 1

Which of the following types of molecules can pass most easily through a biological membrane by simple diffusion? Give an example.

Accepted Answer

Small, nonpolar molecules such as $$O_2$$

Question 2

Which of the following best explains why ions such as $$Na^+$$ and $$Cl^-$$ cannot pass through the lipid bilayer without a transporter?

Accepted Answer

They are repelled by the hydrophobic core of the membrane

Question 3

Aquaporin is an example of which type of membrane transporter?

Accepted Answer

Uniport

Question 4

Which of the following statements about aquaporin is TRUE?

Accepted Answer

It is an integral membrane protein that facilitates passive transport of water.

Question 5

A mutation changes a critical arginine residue in the pore of aquaporin to alanine. What is the most likely effect on intracellular pH?

Accepted Answer

Intracellular pH may decrease due to increased proton leakage.

Question 6

Refer to the hydropathy plot shown. If there are 6 major peaks above the threshold, what does this suggest about the structure of the protein?

Accepted Answer

It is a polytopic membrane protein with 6 transmembrane helices.

Question 7

The molecule shown in the second image is best classified as:

Accepted Answer

A sterol (cholesterol)

Question 8

Which of the following is a correct order of steps in the insulin signaling pathway?

Accepted Answer

Insulin binds receptor → receptor dimerizes and autophosphorylates → SH2 domains bind → SOS activates GEF → GDP is released from Ras → GTP binds Ras → kinase cascade is initiated

Question 9

Why is rapid inactivation of G-proteins by GTP hydrolysis essential for cell survival?

Accepted Answer

It prevents continuous signaling that could lead to uncontrolled cell growth and cancer.

Question 10

Which of the following is a feature of signal transduction regulation?

Accepted Answer

Desensitization, where prolonged exposure to a signal decreases receptor responsiveness.

Question 11

Facilitated diffusion through a biological membrane is:

Accepted Answer

Driven by a difference of solute concentration across the membrane.

Question 12

Carbohydrate residues attached to membrane lipids are almost always:

Accepted Answer

Positioned on the extracellular side of the membrane.

Question 13

Arrange the following fatty acids in order of increasing melting point: palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:3).

Accepted Answer

Linoleic acid, oleic acid, palmitic acid, stearic acid

Question 14

How do G proteins become activated?

Accepted Answer

GDP is exchanged for GTP.

Question 15

The steroid hormones testosterone and beta-estradiol are derived from which lipid molecule?

Accepted Answer

Cholesterol

Question 16

Which compound is NOT a type of membrane lipid?

Accepted Answer

Triacylglycerol

Question 17

Which statement represents a difference between active and passive transport?

Accepted Answer

Active transport requires an external energy source.

Question 18

Which statement concerning fatty acids is true?

Accepted Answer

Lipases release fatty acids from storage so they can be used as fuel.

Question 19

Which statement describes a general feature of the lipid bilayer in all biological membranes?

Accepted Answer

Individual lipid molecules are free to diffuse laterally on the surface of the bilayer.

Question 20

The ion channel that opens to allow $$Na^+$$ and $$Ca^{2+} to $$pass in response to acetylcholine binding is an example of a _____ signal transduction system.

Accepted Answer

Ligand-gated

CHEM 3660 Biochemistry I Exam III Study Guidance

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