Membrane transport

Question 1

What types of molecules can move by simple diffusion across a pure lipid bilayer?

Answer 1

1. Gases (O2, CO2)2. Small, uncharged polar molecules

Question 2

What factors affect rate of diffusion through channels?

Answer 2

1. Permeability2. Selectivity3. Concentration gradient

Question 3

What is carrier-mediated facilitated diffusion (uniport)?

Answer 3

Protein-mediated transport of a single type of molecule down a concentration gradient across a cellular membrane

Question 4

What main differences make uniport different than simple diffusion?

Answer 4

1. Transport rate is higher 2. There is a maximal transport rate Vmax3. Transport is reversible - follows concentration gradient4. Transport is specific

Question 5

What factors determine the rate of initial transport of glucose?

Answer 5

1. Glucose concentration gradient2. Glucose transporter number 3. Affinity of glucose binding to the transporter

Question 6

What is Fick’s law of diffusion?

Answer 6

Rate of diffusion is proportional to (SA x conc grad x mem perm) / membrane thickness

Question 7

What is the equation for membrane permeability?

Answer 7

Lipid solubility / molecular size

Question 8

What are properties of primary active transport?

Answer 8

1. Expenditure of energy and may be inhibited by metabolic inhibitors2. Active transport (but not carrier-mediated diffusion) can transport uncharged substance against a concentration gradient and can transport ions against an electrochemical gradient

Question 9

What are ABC transporters?

Answer 9

1. ATP binding cassettes2. All ABC proteins have a common ATP binding domain 3. Some hydrolyze aTP4. Some use ATP to regulate function 5. Some act as ion channel or regulate ion channels6. Examples: CFTR, MDR

Question 10

What is secondary active transport?

Answer 10

1. Transport of a substance up its concentration gradient is coupled with the downhill movement of another substance rather than a metabolic process2. One substance must move down its electrochemical gradient3. Energy lost by substance moving down gradient is captured and used to transport another substance against its own gradient

Question 11

What are examples of symporters?

Answer 11

1. Two Na / one glucose 2. Na / K / Cl cotransporter3. K / Cl cotransporter4. Na / neurotransmitter cotransporter

Question 12

What are examples of antiporters?

Answer 12

1. Na / Ca exchanger2. Na / H+ exchanger

Question 13

What are the similarities between the membrane transport pathways?

Answer 13

1. Involves a transport protein2. Can only handle small molecules like ions, glucose, amino acids

Question 14

What are properties of fluid phase endocytosis?

Answer 14

1. Uptake of material from extracellular fluid2. No receptors3. Some use clathrin 4. Inefficient way to transport a specific substance

Question 15

What are properties of receptor mediated endocytosis?

Answer 15

1. Clathrin dependent2. Forms coated pits from clathrin

Question 16

What is the main difference between receptor mediated endocytosis and fluid phase endocytosis?

Answer 16

Specificity