DSA 2: Cell Membranes and Transport

Question 1

What is the most important physiological role of the cell membrane?

Answer 1

1. Selective permeability of various metabolites
2. Transport and exchange of materials (nutrients, oxygen, waste, ions)

Question 2

Describe the structure and composition of cell membrane

Answer 2

• Composed of lipids, proteins, and carbs
• Semi permeable
• hydrophilic tail and hydrophobic head

Question 3

What are the two types of phospholipids found in a membrane?

Answer 3

Glycerophospholipid and Sphingolipids

Question 4

What is the structure of a Glycerophospholipid?

Answer 4

-Glycerol backbone with 2 fatty acids and phosphate group

Question 5

What is the structure of sphingolipids?

Answer 5

Sphingosoine backbone with:

1. Hydrocarbon
2. Fatty Acid
3. Phosphate and Choline

Question 6

What is the most common Sphingolipid in the outer leaflet of the PM?

Answer 6

Sphingomyelin

Question 7

Where can you find cholesterol in cell membrane?

Answer 7

Cholesterol is embedded in lipid bilayer. The hydrocarbon side chains interact with hydrophobic tails of lipid membranes.

Question 8

What are the two types of sphingosine?

Answer 8

1. Type of phospholipid (third group is phosphate and choline)
2. Type of glycolipid (third group is a mono or oligosaccarhide - sugar)

Question 9

What is the location and function of Phosphatidylserine in the plasma membrane?

Answer 9

Phosphatidylserine is a type of sphingomyelin

In healthy cells, PS is found in the inner leaflet of bilayer. During apoptosis, PS is displayed on outer leaftlet.

**ON EXAM LAST YEAR

Question 10

What are integral membrane proteins?

Answer 10

Proteins embedded in membrane and stabilized by hydrophobic interactions with lipids.

-includes transporters, ion channels, and receptors

*If they span entire lipid bilayer and interact with both external and internal env. - polytopic transmembrane proteins

Question 11

What are peripheral proteins?

Answer 11

Proteins that are loosely bound to membrane via electrostatic interactions with lipids or proteins.

Question 12

What are lipid anchored proteins?

Answer 12

Proteins tethered to membranes via covalent attachment to a lipid

Question 13

Where can you find carbohydrates on membrane?

Answer 13

They are found extracellularly. Attached via covalently to lipids and proteins

Question 14

What is a glycocalyx and what are its functions?

Answer 14

A carbohydrate shell made up of glycolipids and glycoproteins.

1. Protection
2. Cell adhesion
3. Cell identification

Question 15

What factors influence membrane fluidity?

Answer 15

Remember membrane follows fluid mosaic model.

1. Temperature

High temp: too fluid

Low Temp: too rigid

2. Lipid Composition

Many Saturated FA: decrease fluidity

Unsaturated FA present: increase fluidity

3. Cholesterol (Balancer)

Helps rigid cell membranes by intercalating into membrane to prevent close packing

Helps fluid cell membranes by fitting in the kinks created by the tails of lipids.

Question 16

What are two types of passive transport?

Answer 16

1. Simple Diffusion
2. Facilitated Diffusion

Question 17

What sort of molecules can use Simple Diffusion?

Answer 17

Small molecules that are non-polar, or uncharged polar.

Small Nonpolar Examples

O2, N2, Ethanol, Diethylether, Benzene

Small polar uncharged Examples

Water, CO2, Urea, NH3

Question 18

What are ligand gated channels?

Answer 18

Ion channels that respond to ligands (hormonees or NT)

Allow rapid transport of ions

Question 19

What is Mimantine / Namenda?

Answer 19

Glutamate receptor antagonist (prevents opening of an ion channel)

Treats Alzheimer’s disease

*I think this was on last year exam

Question 20

What are voltage gated ion channels?

Answer 20

Ion channels that open/close in response to membrane potential

*Example: Sodium/Potassium channels in action potentials

Tetradotoxin can bind to sodium channels and inhibit them - lethal! (also anesthetics but they don’t kill you)

Question 21

What are P Type ATPases? (Primary Active Transport)

Answer 21

Energy comes from hydrolysis of ATP (breaks down to ADP+P)

Protein transporter is phosphorlyated which occurs on aspartate residue

Conformational change that facilitates transport of ions from one side to the other

Examples: Na+/K+ ATPase and Ca2+ ATPase

Question 22

What are ABC transporters?

Answer 22

ATP is also hydrolyzed but protein transporter does not get phosphorylated.

Pump out small molecules against gradient concentration

Question 23

What is secondary active transport? What are examples?

Answer 23

Unfavorable flow of one species coupled with Favorable flow of another species - gradient established

Examples: Sodium/Glucose Transporter (SGLT) and Sodium/Calcium Exchanger (NCX)

Question 24

What does SGLT move and how?

Answer 24

Sodium and Glucose

• Both are moved from intestinal lumen to epithelium of SI and renal tubules
• Sodium moves down its gradient
• Glucose moves against its gradient

Question 25

What does NCX transporter move and how?

Answer 25

Moves 3 Sodium into cell (for gradient) and 1 Calcium out of the cell (against gradient)

Question 26

What does GLUT 2 move?

Answer 26

Glucose

Galactose

Fructose

*Facilitated Diffusion

Question 27

What does GLUT 5 move?

Answer 27

Fructose

*Facilitated Diffusion