Module 2

Question 1

What are the functions of a cell membrane?

Answer 1

• act as a physical barrier separating the intracellular and extracellular fluid, and separating the cell from the environment.
• controls entry, elimination, and release of molecules and substances.
• contains proteins that allow for responding or interacting with the external environment.
• provides structural support.

Question 2

What is the cell membrane composed of?

Answer 2

Lipids, proteins, and a small amount of carbohydrates.

Question 3

What are the three types of lipids found in the cell membrane?

Answer 3

Phospholipids, sphingolipids, and cholesterol.

Question 4

What are integral proteins? What are their roles?

Answer 4

Integral proteins include transmembrane proteins and lipid anchored proteins.
They have roles as: membrane receptors, cell adhesion molecules, channels, carriers, pores, pumps, enzymes, and mediators of intracellular signalling.

Question 5

What are peripheral proteins? What are their roles?

Answer 5

Peripheral proteins attach to integral proteins and are loosely attached to the phospholipid head.
Their roles include: participating in intracellular signalling and forming the submembraneous cytoskeleton.

Question 6

What are lipid anchored proteins commonly associated with?

Answer 6

Commonly associated with sphingolipids instead of phospholipids.

Question 7

What are lipid rafts? What are they abundant in?

Answer 7

Lipid rafts help to form the structure of cells. They are abundant in proteins important for cell signal transduction.

Question 8

What is a glycoprotein? What does it do?

Answer 8

A glycoprotein is a protein with carbohydrate attached.

It forms a protective coat, and acts as a structural, transport, or immunologic molecule, and a hormone.

Question 9

What is a glycolipid? What does it do?

Answer 9

A glycolipid is a lipid with a carbohydrate attached.

It serves as a recognition site for cell to cell interactions.

Question 10

Where is cholesterol located in the cell membrane? What does it do?

Answer 10

Cholesterol is positioned between phospholipid heads to add flexibility and help make the membrane impermeable to small water-soluble molecules.

Question 11

What are the concentrations of Na+, K+, Cl-, HCO3-, and proteins in the intracellular fluid?

Answer 11

Low concentrations of Na+, Cl-, and HCO3- (less than 20mmol/L)
High concentrations of K+ and proteins (more than 100mmol/L)

Question 12

What are the concentrations of Na+, K+, Cl-, and HCO3- in the interstitial fluid?

Answer 12

Low concentrations of K+ and HCO3- (less than 30mmol/L)

High concentrations of Na+ and Cl- (more than 100mmol/L)

Question 13

What are the concentrations of Na+, K+, Cl-, HCO3-, and proteins in the plasma?

Answer 13

Low concentrations of K+ and HCO3- (less than 20mmol/L)

High concentrations of Na+, Cl-. and proteins (more than 70mmol/L)

Question 14

What is osmolarity? How does it differ from molarity?

Answer 14

Osmolarity describes the number of particles in solution.
Differs from molarity in the sense that it focuses on osmotically active individual particles as opposed to entire molecules.

Question 15

What does it mean when a solution is isosmotic?

Answer 15

The solutions have identical osmolarities.

Question 16

What does it mean when a solution is hyperosmotic?

Answer 16

It describes the solution with the higher osmolarity.

Question 17

What does it mean when a solution is hyposmotic?

Answer 17

It describes the solution with the lower osmolarity.

Question 18

What is tonicity?

Answer 18

Tonicity describes a solution and how that solution would affect cell volume if a cell were placed in the solution and allowed to come to equilibrium.

Question 19

What is the difference between tonicity and osmolarity?

Answer 19

Tonicity depends on the concentration of non-penetrating solutes, whereas osmolarity depends on both penetrating and non-penetrating solutes.

Question 20

What is diffusion?

Answer 20

The movement of molecules from an area of higher concentration to an area of lower concentration.

Question 21

What does the rate of diffusion across a membrane depend on to be faster?

Answer 21

The rate of diffusion is faster if:

• the membrane’s surface area is larger
• the membrane is thinner
• the concentration gradient is larger
• the membrane is more permeable to the molecule

Question 22

What does a membrane’s permeability to a molecule depend on?

Answer 22

• the molecule’s lipid solubility
• the molecule’s size
• the lipid composition of the membrane

Question 23

What are channel proteins made of? What do they create?

Answer 23

Made of membrane spanning protein subunits that create a cluster of cylinders with a pore through the centre

Question 24

What are carrier proteins? What do they do?

Answer 24

Carrier proteins are large complex proteins that change conformation to move molecules that cannot pass through channels. (slow process)

Question 25

What is facilitated diffusion? In what direction does it move? is energy required?

Answer 25

Diffusion that uses channels or carrier proteins. Molecules move down their concentration gradient. No energy is required.

Question 26

What is active transport? Does it require energy?

Answer 26

Transport that moves molecules against their concentration gradients: from an area of low concentration to an area of high concentration. It requires energy.

Question 27

What is primary active transport? How many Na+ move out? How many K+ move in?

Answer 27

Transport where the energy used to move the molecule comes directly from hydrolyzing ATP (ATPase). 3 Na+ out, 2 K+ in

Question 28

What is secondary active transport? In what direction can it move?

Answer 28

Transport that uses the potential energy stored in the concentration gradient of one molecule to push another molecule against their concentration gradient. Can move in the same direction (symport) or in the opposite direction (antiport).

Question 29

What does specificity refer to?

Answer 29

The ability of a transporter to move one molecule or a closely related group of molecules.

Question 30

What is meant by competition when referring to movement of molecules?

Answer 30

A carrier may move several members of a related group of substances but these substances compete with one another.

Question 31

What is meant by saturation?

Answer 31

The rate of transport depends on the concentration and the number of transporters. Transport normally increases with increasing concentration until the transport maximum is reached.

Question 32

What is vesicular transport?

Answer 32

Macromolecules that cannot fit through a carrier or channel use phagocytosis, endocytosis, or exocytosis with vesicles created from the cell membrane.

Question 33

What is phagocytosis? Does it require energy?

Answer 33

Phagocytosis creates vesicles using the cytoskeleton. It requires ATP.

Question 34

What is endocytosis? Does it require energy?

Answer 34

Endocytosis is transport into a cell. It indents the membrane and the vesicles are much smaller than in phagocytosis. Requires ATP.

Question 35

What is exocytosis? Does it require energy?

Answer 35

Exocytosis is transport out of a cell. It can occur continuously or intermittently when initiated by some sort of signal. Requires ATP and can be regulated by Ca^2+

Question 36

What is transcellular transport?

Answer 36

Transport across epithelial cells. Requires energy.

Question 37

What is paracellular transport?

Answer 37

Transport between tight junctions. Does not require energy.

Question 38

What is transcytosis?

Answer 38

Transport of larger substances. Requires energy.

Question 39

What is membrane potential?

Answer 39

The electrical disequilibrium that exists between the extracellular fluid and the intracellular fluid.

Question 40

What is an electrochemical gradient?

Answer 40

The combination of electrical and concentration gradients.

Question 41

What is the equilibrium potential?

Answer 41

The membrane potential that exactly opposes the concentration gradient in any given concentration gradient of a single ion.

Question 42

What two factors influence a cell's membrane potential?

Answer 42

The concentration gradients of different ions across the membrane and the permeability of the membrane to those ions.