Chp 11 - Membranes

Question 1

Give 3 functions of membranes.

Answer 1

Separation of cellular compartments, responsible for generating and maintaining ion and small molecule gradients, assists with the biosynthesis and delivery of transmembrane proteins

Question 2

___________ (2) are the main structural component of all biological membranes.
The major lipid components are ______________.
They form spontaneously as a result of __________ interactions.

Answer 2

Lipid bilayers; glycerophospholipids; hydrophobic

Question 3

Give 3 classes of Membrane-Associated Proteins.

Answer 3

Integral membrane proteins (transmembrane proteins), Peripheral membrane proteins, Lipid-anchored membrane proteins

Question 4

What is the lipid-to-protein ratio of a typical membrane?

Answer 4

25-50% lipid
50-75% protein
<10% carbohydrate

Question 5

What is the major lipid components?

Answer 5

Glycerophospholipids, which form an asymmetrically bilayer ~5-6nm thick. It provides structural support, creating two distinct layers due to the hydrophobic interactions of lipid tails. Follows the fluid-mosaic model, allowing for rapid rotation and diffusion of their components.

Question 6

Describe three modes of transport mechanisms.

Answer 6

Pores and channels, facilitated diffusion, and active transport.

Question 7

What is the difference between facilitated diffusion and active transport?

Answer 7

Facilitated diffusion does not need energy and only moves substances down the gradient, while active transport needs energy to move substances against their gradient.

Question 8

What is endocytosis and exocytosis?

Answer 8

Endocytosis and exocytosis are processes for large molecule transport; endocytosis involves the cell engulfing substances into vesicles, while exocytosis releases contents outside the cell by vesicle fusion with the membrane.

Question 9

What are the enzymes that catalyze transverse diffusion of membrane phospholipids?

Answer 9

Flippase (ECM → cytosol) and floppase (cytosol → ECM) are the enzymes that catalyze transverse diffusion of certain phospholipids (normally very slow).

Question 10

Membrane fluidity is largely dependent on the flexibility of _____________ including: (3)

Answer 10

Fatty acid sidechains.
A) Increased temperature increases fluidity
B) Unsaturated fatty acyl groups do not pack as tightly, increase fluidity
C) The amount of cholesterol (20-25% mass of mammalian membrane lipids)

Question 11

List four general observations that describe membrane transport.

Answer 11

*Hydrophobic small molecules can freely diffuse across membranes
*Small ions (e.g. Na+, Cl-) cannot diffuse without assistance (H+ is significantly easier to diffuse (for an ion))
*Biological macromolecules are intermediate
*Nonpolar gases freely diffuse

Question 12

What are the three sub-classes of lipid-anchored membrane proteins?

Answer 12

Glycosylphosphatidylinositol (GPI)-anchored proteins, fatty acyl-anchored proteins, and prenyl-anchored proteins.

Question 13

Flippase process is…
Floppase process is…

Answer 13

(ECM → cytosol)
(cytosol → ECM)

Question 14

List the types of membrane transport mechanisms.

Answer 14

Simple diffusion, channels and pores, passive transport, active transport: primary and secondary.

Question 15

Passive diffusion rate or flux depends on what?

Answer 15

The magnitude of concentration gradient across the GI and vascular membrane (C1-C2), membrane surface area, membrane thickness, partition coefficient of the drug, and drug diffusion coefficient.

Question 16

For Fick’s Law of Diffusion, what does the permeability coefficient consider?

Answer 16

The partition coefficient of the drug, and drug diffusion coefficient.