L2 Cell Membrane Transport

Question 1

What are all the types of molecules that pass through the membrane?

Answer 1

1. Hydrophobic
2. Small molecules
3. Large molecules
4. Ions

Question 2

What molecules are allowed to pass through the membrane by membrane proteins?

Answer 2

Membrane proteins allow polar and charged molecules to pass through the membrane.

Question 3

What are the two major membrane transport processes?

Answer 3

Passive transport and Active transport.

Question 4

Which processes uses passive transport? What is the energy source of passive transport?

Answer 4

1. Process - Simple and Faciliated diffusion
2. Energy source - Concentration Gradient

Question 5

Which direction does the solute move in relation to its electrochemical gradient?

Answer 5

Moves down the electrochemical gradient

Question 6

What is the type of solute and transport protein involved in osmosis?

Answer 6

Solute is water and transport proteins are aquaporins.

Question 7

What is the type of solute and transport protein involved in facilitated diffusion?

Answer 7

Solutes are large and charged ion such as glucose, amino acids, they require channel proteins to pass through the membrane

Question 8

What is the type of solute and transport protein involved in simple diffusion?

Answer 8

Solutes are: small uncharged molecules like O2, CO2 and lipids. No transport proteins are involved

Question 9

Which processes use active transport? What is the energy source, the direction of solute in relation to its electrochemical gradient?

Answer 9

1. Process - Primary (Direct) and secondary (Indirect)
2. Energy source is ATP
3. Solutes move against their electrochemical gradient that means from a lower concentration to higher concentration.

Question 10

What type of solute and transport proteins are involved in active transport?

Answer 10

1. Types of solute are ions (Sodium, potassium and calcium), nutrients (Glucose, amino acids) and larger molecules (Proteins).
2. Transport proteins - Carrier proteins and ion pumps eg. NaK Pump.

Question 11

What is the difference between primary and secondary active transport?

Answer 11

Primary needs ATP
Secondary uses the energy stored in the electrochemical gradient.

Question 12

What does passive transport depend on?

Answer 12

Concentration Gradient.

Question 13

Explain simple diffusion

Answer 13

Movement of substances from a high concentration to a low concentration

Question 14

What is Flux (Jx) and what does it depend on?

Answer 14

Flux- how fast solute X moves across a cell membrane. Flux depends on permeability coefficient of X and difference in concentration of X between ICF and ECF.

Question 15

What do transmembrane proteins do and what are they made up of?

Answer 15

Transmembrane protein move hydrophilic solutes in and out of the membrane. They are composed of membrane - spanning alpha - helical domains

Question 16

What does topology mean?

Answer 16

Topology is how protein move in and out of the membrane.

Question 17

What are the types of transmembrane proteins?

Answer 17

1.Pore ( Non-gated channel)
2. Channel (Gated-pore)
3. Carrier
4. Pump

Question 18

How do transmembrane proteins transport substances?

Answer 18

Transmembrane proteins create hydrophilic permeation pathways through the membrane

Question 19

What does the hydrophilic permeation pathways consist of?

Answer 19

They consist of amphipathic helices with alternating hydrophobic and hydrophilic amino acids

Hydrophobic faces the lipid membrane and hydrophilic creates a central pore.

Question 20

What do pores do and what are the driving forces?

Answer 20

Pores allow faciliated diffusion (Passive Transport)
The driving force is the electrical chemical gradient

Question 21

What do channels do and what are the driving forces?

Answer 21

Channels allow faciliated diffusion (Passive transport) and the driving force is the electrochemical gradient.

Question 22

What is the major difference between pores and channels?

Answer 22

Pores are always open and channels have gated ion channels.

Question 23

What are the types of channels?

Answer 23

The types of channels are:
1. Voltage gated
2. Ligand gated intracellular
3. Ligand gated extracellular
4. Mechanical gated

Question 24

What does each channel have?

Answer 24

Each channel has:
1. A moveable gate
2. A sensor (ligand, voltage or mechanical)
3. A selectivity filter
4. An open channel pore.

Question 25

What do carriers do and what are the driving forces? Give examples of carriers?

Answer 25

Carriers allow faciliated diffusion and the driving force is the electrochemical gradient. Eg. GLUT

Carriers never have a continous transmembrane path

Question 26

Carrier’s faciliated diffusion is slow. Why is that?

Answer 26

Binding and confrontational changes
Limited number of binding sites competition for binding sites.

Question 27

What other components do carriers use to mediate active transport?

Answer 27

They use pumps, co transporters and exchangers.

Question 28

What do cotransporters do? E.g.?

Answer 28

Co transporters move both solutes in the same direction using the energy provided by the electrochemical gradient. Eg. Na+ glucose cotransporter.

Symporters - same direction

Question 29

What do exchangers do? Eg?

Answer 29

Exchangers move solute in the opposite direction using the driving solute whose electrochemical gradient provides the energy. eg. Na+/Ca2+ exchangers.

Antiporters - opposite directions

Question 30

Flux (Jx) can be limited by 2 factors. What are these factors?

Answer 30

Number of carriers in the membrane
Speed by which the carrier can cycle through the steps

Question 31

How can carriers mediate active transport?

Answer 31

They mediate active transport through the use of pumps, cotransporters and exchangers

Question 32

What types of protein carriers do primary and secondary active transport use?

Answer 32

Primary active transport - pumps
Secondary active transport - cotransporters and exchangers