Chapter 7: Membrane Structure and Function

Question 1

What is the plasma membrane?

Answer 1

surrounds the cell and controls all inbound and outbound traffic

Question 2

Selective Permeability

Answer 2

allowing some substances to cross it more easily than others

Question 3

Why is the plasma membrane selectively permeable?

Answer 3

the ability of the cell to discriminate in its chemical exchanges is fundamental life

Question 4

amphipathic

Answer 4

it has both a hydrophilic region and a hydrophobic region

Question 5

Fluid Mosaic Model

Answer 5

accepted model of cell membrane structure as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids

Question 6

What can impact the fluidity of the cell membrane?

Answer 6

a. cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinders solidification by disrupting the regular packing of phospholipids
b. temperature at which membrane solidifies depends on types of lipids — unsaturated hydrocarbon tails remains fluid at low temperatures

Question 7

Peripheral Proteins

Answer 7

membrane proteins that aren’t embedded in the lipid bilayer; they are loosely bound on the surface or exposed to integral proteins

Question 8

Integral Proteins

Answer 8

membrane proteins that penetrate the hydrophobic interior of the lipid bilayer

Question 9

What are six functions of cell surface membrane proteins?

Answer 9

a. Transport
b. Enzymatic activity
c. Signal transduction
d. Cell-cell recognition
e. Intercellular joining
f. Attachment to the cytoskeleton and ECM

Question 10

How do cells recognize each other?

Answer 10

Cells recognize other cells by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane

Question 11

How do glycoproteins and glycolipids form?

Answer 11

a. Membrane proteins and lipids are synthesized in association with the ER; carbohydrates are added to the transmembrane proteins (glycoproteins).
Next inside the Golgi apparatus, the glycoproteins undergo further carbohydrate modification, and lipids acquire carbohydrates, becoming glycolipids.

Question 12

The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when?

Answer 12

It is determined as the membrane is being built by the endoplasmic reticulum and Golgi apparatus. As vesicle fuse with the plasma membrane, the secretory proteins are released from the cell, and positions the carbohydrates of membrane glycoproteins and glycolipids on the outside (extracellular) face of the plasma membrane.

Question 13

Membranes have distinct inside and outside faces (TorF)

Answer 13

True

Question 14

Which type of molecules can pass through the membrane easily?

Answer 14

Nonpolar molecules are hydrophobic like the inner lipid bilayer, and can cross membrane easily

Question 15

Transport Proteins

Answer 15

transmembrane protein that allows hydrophilic substances can avoid contact with the lipid bilayer by passing through. (transport protein is specific for the substance it translocates, allowing only a certain substance to cross the membrane)

Question 16

What are channel proteins?

Answer 16

Some transport proteins function by having a hydrophilic channel that certain polar molecules or atomic ions us as a tunnel through the membrane

Question 17

What are aquaporins?

Answer 17

Transport protein that greatly facilitates (increasing the rate) the passage of water molecules through the membrane

Question 18

What are carrier proteins?

Answer 18

Transport proteins that hold onto their passengers and change shape in a way that shuttles them across the membrane

Question 19

What is diffusion?

Answer 19

the random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated. [PASSIVE TRANSPORT]

Question 20

What is a concentration gradient?

Answer 20

The region along which the density of a chemical substance increases or decreases unaffected by the concentration gradients of other substances (driven by potential energy)

Question 21

What is osmosis?

Answer 21

The diffusion of free water across a selective permeable membrane, whether artificial or cellular

Question 22

How does osmosis work?

Answer 22

Tight clustering of water molecules around hydrophilic solute molecules makes some of the water unavailable to cross membrane. As a result, the solution with a higher solute concentration has a lower free water concentration. Water diffuses across the membrane from the region of higher free water concentration (lower solute concentration) to that of lower free water concentration (higher solute concentration).

Question 23

Isotonic solution

Answer 23

Water diffuses across the membrane, but at the same rate in both directions (no net movement), because environment has same concentration across the membrane.

Question 24

Hypertonic solution

Answer 24

Solution has higher concentration than the cell; the cell (higher free water concentration/lower solute concentration) will lose water, shrivel and possibly die.

Question 25

Hypotonic solution

Answer 25

Solution has lower concentration than the cell; the cell (lower free water concentration/higher solute concentration) will swell and lyse (burst) because water will enter the cell faster than it leaves.