The Cell Membrane and its Transport Systems

Question 1

What are the two main types of membrane transport mechanisms?

Answer 1

1. PASSIVE
simple diffusion, facilitated diffusion, osmosis
2. ACTIVE
primary, 
secondary: 
a. cotransport/symport
b. counter-transport /antiport/exchanger

Question 2

Transport proteins - 3 main types:

Answer 2

1. pores (=FD. always open, integral, non-gated)
2. channels (=FD. single gated - eg VG, LG, mechanical gated)
3. carriers (= AT or FD, double gated)

Question 3

Integral proteins that are always open, called __________________

Answer 3

1. Pores.

eg. aquaporins

Question 4

Transport proteins with gated pore at one end, are called __________________

Answer 4

2. Channels
   • Voltage-gated, mechanical -gated, ligandgated (neurotransmitter, nucleotide, phosphorylation) nucleotide, phosphorylation)
   Eg. most ion channels

Question 5

How does Na VG channel work?

Answer 5

At resting potential, VGNC are closed. when the membrane is depolarized, conformational changes open the VGNC.

Question 6

Double gated transport proteins are called ___________________.

When ATP attaches to receptor the substrate enters due to conformational change to the protein.

Answer 6

3. Carriers

Eg. NA-K ATPase
CFTR.

Question 7

Characteristics of transport proteins

Answer 7

• exhibit saturation kinetics.

- exhibit specificity (can be inhibited by structural analogs)

Question 8

Secondary Active Transport:

Answer 8

An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients,

Question 9

Difference between primary and secondary active transport?

Answer 9

In primary active transport, the energy is derived directly from the breakdown of ATP. In the secondary active transport, the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences between the two sides of a membrane.

Question 10

What are the different types of ATPases? (Primary Active Transporters)

Answer 10

1. P type = Pi binds for short time, causes conformational change. eg. NKA, HK pump, PMCA, SERCA
2. F type = can synthesise ATP, pumps H+ ions into matrix. found in inner mitochondrial membrane
3. V-type = cannot sunthesisze ATP, found in vacuoles and vesicles. pumps H+ from cutoplasm to the organelle’s interior.
4. ABC transporters = ATP binding casettes. eg. CFTR.

Question 11

difference between P-, F-, V- and ABC?

Answer 11

The P-, F- and V-classes only transport ions, while the ABC superfamily also transports small molecules.

Question 12

What is the E1/E2 ATPase?

Answer 12

its the same as P-type ATPase

Question 13

Na-K ATPase/pump

Answer 13

3 Na+ out, 2 K+ in.

treatment for heart failure, comes from plant Digitalis.

Question 14

Which is the only primary ATer for Na+?

Answer 14

Na-K ATPase

Question 15

Which is the most important primary active transport mechanism for K+?

Answer 15

Na-K ATPase

Question 16

ABC transporter superfamily

Answer 16

may act as pumps, channels, or regulators, of:

1. ABCA1 = transports cholesterol and PSPL from macrophages etc.
2. MDRs = multidrug resistance transporters. - responsible for decreasing drug accumulation. aka P-glycoprotein. found in kidney, GI, BBB, liver. overexpressed in cancer cells.
3. CFTR

Question 17

CFTR

Answer 17

With two membrane spanning domains and two nucleotide binding domains (NBDs)
• R Domain = regulatory domain
• (1) Presence of ATP in NBD and (2) phosphorylation of Rdomain increases probability of opening the chloride channel

it is present in apical membrane of EpC’s especially in lungs.
transport Cl-

Question 18

In CF:

1) in skin Cl- cant go _________
2) in trachea Cl- cant go ________

Answer 18

1) back in

2) out

Question 19

What are the two main classes of secondary active transport?

Answer 19

1. COTRANSPORTER/SYMPORTERS
   eg SGLT in kidney tubules and intestines
2. COUNTERTRANSPORTERS/ANTIPORTERS
   eg. Na-Ca exchanger (NCX), Na-H exchnager (NHE)