Physiology Membrane Lecture 2 - Membrane Transport?

Question 1

What is meant bye there term that the plasma membrane is selectively permeable?

Answer 1

Its is impermeable to some molecules and ions but permeable to others.

Question 2

What two properties influence wether a particle can permeate the plasma membrane without assistance?

Answer 2

1. Solubility of the particle in lipid

2. Size of the particle

Question 3

What are the two types of driving forces of membrane transport

Answer 3

Passive and active

Question 4

What is passive membrane transport?

Answer 4

When no energy is needed

Question 5

What is active membrane transport?

Answer 5

Requires the cell to expend energy (ATP) to produce movement

Question 6

What two forces drive molecules that can passively penetrate membrane?

Answer 6

1. Diffusion down a concentration gradient
2. Movement along an electrical gradient!

Molecules and ions can be affected by on or both of these forces!

Question 7

When is a dynamic equilibrium reached?

Answer 7

When diffusion in both directions is equal

Question 8

What is Fick’s Law of Diffusion?

Answer 8

It predicts the rate of diffusion across a lipid bilayer

Question 9

What factors affect Fick’s Law of Diffusion?

Answer 9

1. The magnitude of the concentration gradient. (The bigger the concentration the bigger the rate)
2. The surface area of the membrane across which diffusion is taking place. (The larger the surface area the larger the rate)
3. The lipid solubility of the substance. (The more lipid soluble the larger the rate)
4. The molecular weight of the substance. ( Smaller particle diffuse more easily)
5. The distance through which diffusion must take place. (Normally relatively constant for cell membranes)

Question 10

What is the equation for Fick’s Law of Diffusion?

Answer 10

Q = deltaC x A x P

Q = net rate of diffusion
deltaC = concentration gradient
A = surface area of membrane
P = permeability

Question 11

Give an example of movement of an ion by the electrical gradient.

Answer 11

cations (positively charged) tend to move towards negatively charged areas

Question 12

What generates an electrical gradient?

Answer 12

A difference in charge between two adjacent areas

Question 13

Even when an electrical gradient exist between ICF and ECF why might movement not occur?

Answer 13

Movement may not occur as only ions that can permeate the membrane will move along the gradient.

Question 14

What is osmosis?

Answer 14

It is the net diffusion of water down its own concentration gradient, from high to low!

Question 15

What are aquaporins?

Answer 15

Water channels

Question 16

Water molecule are polar so very soluble in lipids so how do they permeate the plasma membrane more readily than expected?

Answer 16

Water molecules are small enough to slip between the fatty acids of the lipid bilayer

Question 17

What is osmolarity?

Answer 17

It is the concentration of osmotically active particles present in a solution e.g. An increase in water decreases the solute concentration so osmolarity decreases.

Question 18

What is tonicity?

Answer 18

It is the effect a solution has on cell volume e.g. Isotonic, hypertonic and hypotonic!

Question 19

What does isotonic mean?

Answer 19

Two solution having the same osmotic pressure e.g. A red blood cell in a isotonic solution will have no net movement of water.

Question 20

What does hypertonic mean?

Answer 20

One fluid having a higher osmotic pressure than the other e.g. a red blood cell in a hypertonic solution will have a decrease of cell volume as water will move from inside the cell to outside the cell causing it to shrink.

Question 21

What does hypotonic mean?

Answer 21

One fluid having a lesser osmotic pressure than the other e.g a red blood cell in a hypotonic solution will have an increase in cell volume as water will move inside the cell causing it to swell.

Question 22

What is carrier mediated transport?

Answer 22

When a substance binds onto a specific carrier which undergoes a conformational change (shape change) which transports the substance

Question 23

What are the three important characteristics that determine the kind and amount of material transferred across the membrane?

Answer 23

1. Specificity - Each carrier is specialised to transport a specific substance or a few closely related chemical compounds e.g. Cysteinuria
2. Saturation - Transport maximum (™). Only a certain amount of substrate can be moved at at time e.g. Renal glucose re-absorption
3. Competition - When two substrates, both using the same transport, are present e.g. An amino acid carrier can transport both Gly and Ala. The presence of both diminishes the rate of transfer for either.

Question 24

Describe the characteristic of carrier mediated transport: Specificity!

Answer 24

Each carrier is specialised to transport a specific substance or a few closely related chemical compounds. E.g. Cysteinuria

Question 25

Describe the characteristic of carrier mediated transport: Saturation!

Answer 25

Saturation - Transport maximum (™). Only a certain amount of substrate can be moved at at time e.g. Renal glucose re-absorption

Question 26

Describe the characteristic of carrier mediated transport: Competition!

Answer 26

When two substrates, both using the same transport, are present. An amino acid carrier can transport both Gly and Ala. The presence of both diminishes the rate of transfer for either.

Question 27

Which method is faster and more efficient, facilitated diffusion (career mediated) or simple diffusion?

Answer 27

Facilitated diffusion is has a greater rate and reachers saturation first. This means it is more efficient.

Question 28

What are the two forms of carrier mediated transport?

Answer 28

1. Facilitated diffusion

2. Active transport

Question 29

Describe the carrier mediated transport: facilitated diffusion!

Answer 29

Facilitated diffusion uses a carrier to facilitate (assist) the transfer of a substance across the membrane ‘downhill’ from high to low concentration.
Does not require energy!

Question 30

Describe the carrier mediated transport: active transport!

Answer 30

Active transport requires the carrier to expend energy to transfer a substance ‘uphill’ against a concentration gradient. Requires the input of energy!

Question 31

What are the two forms of active transport?

Answer 31

1. Primary active transport

2. Secondary active transport

Question 32

Describe primary active transport!

Answer 32

Energy (usually hydrolysis of ATP) is directly required to move a substance against its concentration gradient. E.g. NaK pump! or the Ca pump found in the plasma membrane of nerve terminals

Question 33

Describe secondary active transport!

Answer 33

Energy is required, but it is not used directly to produce ‘uphill’ movement. The carrier does not split ATP – instead it moves a molecule ‘uphill’ by using secondhand energy stored in the form of an ion concentration gradient (usually a Na+ gradient (as there are always more Na+ outside the cell than inside) or another existing concentration gradient)

Question 34

Describe the Na+ K+ Pump!

Answer 34

More complicated primary active transporter.
Found in the plasma membrane of all cells.
Transports 3x Na+ out of the cell for every 2x K+ in.

Question 35

What are the three important roles for the Na+ K+ pump?

Answer 35

1. Helps establish Na+ and K+ concentration gradients across the plasma membrane of all cells.
2. Helps regulate cell volume by controlling concentration of solutes inside the cell.
3. The energy used to drive the pump indirectly serves as the energy source for secondary active transport.

Question 36

What is the definition of secondary active transport?

Answer 36

Definition: The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (typically Na+).

Question 37

What are the two mechanism of secondary active transport?

Answer 37

1. Symport (co-transport)

2. Antiport (exchange or counter transport)

Question 38

Describe the secondary active transport: symport or co-transport!

Answer 38

The solute and ion (Na+) move in the same direction across the plasma membrane. E.g. glucose absorption at the apical membrane of enterocytes

Question 39

Describe the secondary active transport: anti port or exchange or countertransport!

Answer 39

The solute and ion (Na+) move in opposite directions across the plasma membrane (Na+ into, solute out of the cell). E.g. cells exchange Na+ and H+ by means of antiport, important in regulation of intracellular pH.

Question 40

What is energy required for in vesicular transport?

Answer 40

It is required for vesicle formation and movement within the cell (active).

Question 41

What are the two types of vesicular transport?

Answer 41

1. Endocytosis

2. Exocytosis

Question 42

What is endocytosis?

Answer 42

‘Pinching off’ of membrane to engulf substance. Moving substances inside cell from outside.

Question 43

What is exocytosis?

Answer 43

A vesicle fuses with the plasma membrane, releasing its contents to the ECF.
E.g Secretion of enzymes, protein hormones and a way of adding carriers, channels or receptors to the plasma membrane (E.g. GLUT4 & insulin) It is the Moving of substances from inside the cell to outside the cell.