L2 Cell Membrane Transport

Question 1

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

Answer 1

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

Question 2

What are 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

What process does passive transport use? What is the energy source, the direction of solute in relation to its electrochemical gradient?

Answer 4

1. Process - Simple and Faciliated diffusion
2. Energy source - Concentration Gradient
3. Direction - Down the electrochemical Gradient.

Question 5

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

Answer 5

1. Simple Diffusion: Solutes are small uncharged molecules like O2, CO2 and lipids, they can pass through the membrane,
2. Faciliated Diffusion: Solutes are large and charged ion such as glucose, amino acids, they require channel proteins to pass through the membrane
3. Osmosis: Solute is water and transport proteins are aquaporins.

Question 6

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

Answer 6

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 7

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

Answer 7

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 8

What is the difference between primary and secondary active transport?

Answer 8

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

Question 9

Passive transport depends on?

Answer 9

Concentration Gradient.

Question 10

Explain Simple diffusion

Answer 10

Movement of substances from a high concentration to a low concentration

Question 11

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

Answer 11

How fast the solute X moves can be described as its flux, flux depends on permeability coefficient of X and difference in X between ICF and ECF.

Question 12

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

Answer 12

Transmembrane protein move hydrophilic solutes in and out of the by single or multi pass, they are composed of membrane spanning alpha - helical domains and classed as integral membrane proteins.

Question 13

What does Topology mean?

Answer 13

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

Question 14

What are the types of transmembrane proteins?

Answer 14

Pore ( Non-gated channel), Channel (Gated-pore), carrier and pump.

Question 15

How do transmembrane proteins transport substances?

Answer 15

Transmembrane proteins create hydrophilic permeation pathways through the membrane

Question 16

What do the hydrophilic permeation pathways consist of?

Answer 16

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

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

Question 17

What do pores do and what are the driving forces?

Answer 17

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

Question 18

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

Answer 18

Channels allow faciliated diffusion (Passive Transport) and the driving force is the electrochemical gradient. E.g. Potassium ion channels.

Question 19

What is the major difference between pores and channels?

Answer 19

Pores are always open and channels have gated ion channels.

Question 20

What are the types of channels?

Answer 20

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

Question 21

What does each channel have?

Answer 21

Each channel has a moveable gate, a sensor (ligand, voltage or mechanical), a selectivity filter and an open channel pore.

Question 22

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

Answer 22

Carriers allow faciliated diffusion (Passive Transport) and the driving force is the electrochemical gradient. Eg. GLUT, they never have a continuous transmembrane path.

Question 23

Carrier’s faciliated diffusion is slow why is that?

Answer 23

Binding and confrontational changes, limited number of binding sites and competition for binding sites.

Question 24

What other components do carriers use to mediate active transport?

Answer 24

They use pumps, co transporters and exchangers.

Question 25

What do co transporters do? E.g.?

Answer 25

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 26

What do exchangers do? Eg?

Answer 26

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

Antiporters - opposite directions