Forces Acting Across the Membrane

Question 1

What two fluid compartments of the body does the cell membrane separate?

Answer 1

ECF and ICF

Question 2

How permeable is the cell membrane to ions?

Answer 2

Not at all

Question 3

What proportions of Total body water are found in the extracellular and intracellular fluid?

Answer 3

1/3 in the ECF

2/3 in the ICF

Question 4

How do the concentrations of sodium and potassium ions differ in the ECF and ICF?

Answer 4

[K] is high in the ICF and lower in the ECF

[Na] is higher in the ECF and lower in the ICF

Question 5

Are cell membranes rigid or flexible?

Answer 5

Flexible- (oil like)

Question 6

What are the four general classes of membrane proteins?

Answer 6

1. Receptors
2. Transporters
3. Peripheral proteins
4. Enzymes

Question 7

What is the collective name given to receptor proteins, transport proteins and enzymes?

Answer 7

Integral Membrane proteins

Question 8

What is meant by the term ‘integral membrane protein’?

Answer 8

A protein which is integrated into the bilayer of the membrane, spanning the hydrophobic core. it cannot be extracted without disturbing the membrane.

Question 9

What is the role of receptor proteins?

Answer 9

Communicate and extracellular signal to the intracellular space to produce a cellular response.

Question 10

What are the two types of transport proteins?

Answer 10

Channel proteins and Carrier proteins

Question 11

Describe how channel proteins allow transport of molecules across the cell membrane.

Answer 11

• Create a continuous pore through membrane, through which specific molecules can flow (usually ions)
• Can be open or gated

Question 12

Describe how carrier proteins allow transport of molecules across the cell membrane.

Answer 12

• Binding of a molecule to the carrier protein causes it to change formation.
• Changes it from being open to ECF to being open to ICF
• Used for transport of larger molecules than channel proteins (e.g. glucose)

Question 13

What is meant by peripheral membrane proteins?

Answer 13

Proteins which are not incorporated into the cell membrane but which are associated with it, on wither the internal or external side.

Question 14

What are the three main roles of peripheral membrane proteins?

Answer 14

• Maintain structure of cell by anchoring cell membrane to intracellular cytoskeleton
• Attach to extracellular matrix
• Perform signalling functions within cells- transmit signals from extracellular to intracellular side.

Question 15

What is the role of membrane carbohydrates?

Answer 15

Recognition of ‘self’ and ‘non-self’ material

Question 16

What is meant by the ‘electrochemical gradient’?

Answer 16

Sum of the electrical and chemical gradients

Question 17

What are the 5 mechanisms of movement across a cell membrane?

Answer 17

1. Endo/exocytosis
2. Diffusion
3. Mediated transport (facilitated diffusion and active transport)
4. Osmosis
5. Filtration (across capillary walls)

Question 18

Describe the process of endocytosis.

Answer 18

Invagination of cell membrane to enclose molecules in vesicle which eventually pinches off from intracellular side of cell membrane to enter to ICF and migrate to destination.

Question 19

Describe the process of exocytosis.

Answer 19

Fusion of vesicle with cell membrane to release contents extracellularly.

Question 20

What criteria must a molecule meet to diffuse through a lipid bilayer?

Answer 20

Must be a small, uncharged, hydrophobic (lipophilic) molecule

Question 21

What is the difference between a voltage and a ligand gated ion channel?

Answer 21

Ligand gated relies on chemical stimuli, voltage gated relies on electrical stimuli.
Ligand gated channels will open or close depending on whether or not a specific chemical has bound to their receptor binding site.
Voltage gated channels will open or close based on changes in membrane electrical potential.

Question 22

What type of membrane proteins are incorporated into a ligand gated ion channel?

Answer 22

Receptor and transport proteins

Question 23

What is the difference between osmolarity and tonicity?

Answer 23

Osmolarity describes the total number of particles in solution.
Tonicity describes the number of non-penetrating particles in solution. It is this which determines cell volume.

Question 24

What is meant by the term ‘hypotonic’?

Answer 24

A solution with fewer non- penetrating particles.

Question 25

What is meant by the term ‘hypertonic’?

Answer 25

A solution with more non- penetrating particles.

Question 26

What is the tonicity of normal human ECF?

Answer 26

285 (300) mosmol/ L

Question 27

What is a safe dosage of saline to administer to a patient of normal ECF tonicity?

Answer 27

0.9% 150mM

Question 28

In what direction would water move if a cell was placed in a hypotonic solution?

Answer 28

Water would move into the cell, causing it to swell.

Question 29

In what direction would water move if a cell was placed in a hypertonic solution?

Answer 29

Water would leave the cell, causing it to shrink.

Question 30

What would happen to the volume of red blood cells in a patient with uraemia? (excess urea in their plasma)

Answer 30

It may be expected that the penetrating urea particles would move into the RBCs, creating an osmotic pull and so causing water to also move into the RBCs, increasing their volume.
However, in vivo, plasma contains enough non- penetrating particles to hold water in ECF. Urea will move into RBCs, but water will not follow.