Forces Acting Across Membranes 1

Question 1

What does the cell membrane do?

Answer 1

Separates ECF and ICF and is responsible for maintaining the difference in composition

Question 2

What is a major difference between the ECF and the ICF?

Answer 2

The chemical composition

Question 3

What is the ECF sub-divided into?

Answer 3

Plasma and interstitial fluid

Question 4

What is ratio of Total body water in the ECF compared to the ICF?

Answer 4

• ECF= 1/3 TBW (combined 14L)

- ICF=2/3 TBW (combined 28L)

Question 5

How does gas pass across the capillary wall and cell membrane?

Answer 5

Freely

Question 6

How do nutrients and waste pass across the capillary wall and cell membrane?

Answer 6

Pass easily but sometimes with help from membrane proteins

Question 7

How does water pass across the capillary wall and cell membrane?

Answer 7

There is no barrier to water

Question 8

How do ions pass across the capillary wall and cell membrane?

Answer 8

• Pass freely across the capillary wall so exchange readily between plasma and ISF
• They do not penetrate the cell membrane

Question 9

Describe the concentrations of K and Na ion in the ICF and ECF.

Answer 9

• K is high in the ICF, low in the ECF

- Na is low in the ICF, high in the ECF

Question 10

In what way does the distribution of solutes differ in the plasma and the ISF?

Answer 10

In their protein concentration

Question 11

What is meant by the cell membrane being a selective barrier?

Answer 11

It is freely permeable to some substances such as O2 and CO2 but the difference I composition between ECF and ICF shows that permeability is selective and not universal

Question 12

What is the cell membranes ability to vary permeability important for?

Answer 12

Various cell functions including transmission of nerve impulses

Question 13

How do membranes provide binding sites for chemical recognition?

Answer 13

Embedded in cell membranes are receptors for chemical signals such as hormones and neurotransmitter which regulate cellular activity.

Question 14

What tissues can respond to a hormone/ neurotransmitter signal?

Answer 14

lOnly tissues that express receptor for the specific hormone/neurotransmitter

Question 15

What is meant by membranes being dynamic?

Answer 15

They are continually being formed and maintained or dismantled and metabolised according to the needs of the cell.

Question 16

What is the structure of the cell membrane?

Answer 16

-Very thin bi-layer of phospholipids

Question 17

Describe the structure of a phospholipid.

Answer 17

Hydrophilic phosphate heads and hydrophobic fatty acid tails.

Question 18

How do phospholipids arrange themselves in an aqueous environment?

Answer 18

Their polar part is on the outside of the membrane and the fatty acid chains are on the inside

Question 19

Lipophobic

Answer 19

Lipid repellent and hydrophlic

Question 20

Lipophyllic

Answer 20

Lipid loving and hydrophobic

Question 21

What is embedded in the phospholipid bilayer?

Answer 21

Proteins

Question 22

Why are membranes flexible?

Answer 22

Fatty acids in vivo behave like an oil and therefore can stretch , although may rupture if over stretched

Question 23

What is meant by membranes being insulators against movement of electrical charges?

Answer 23

They prevent the passage of electrons which is important in maintaining electrical stability of a cell

Question 24

What are the 4 general classes of membrane proteins?

Answer 24

Receptors
Transporters
Enzymes
Peripheral proteins

Question 25

What are receptors, enzymes and transporters otherwise known as?

Answer 25

The integral membrane proteins

Question 26

What are integral membrane proteins?

Answer 26

Proteins that are integrated into the structure of the membrane, typically spanning the hydrophobic core and cannot be extracted without disturbing the membrane

Question 27

What are peripheral proteins?

Answer 27

They are proteins associated with the membrane but not incorporated into it. They do not span the hydrophobic core

Question 28

What do receptors do?

Answer 28

Allow communication of an extracellular signal to the intracellular space to create response

Question 29

What are transporters?

Answer 29

Proteins which allow movement of ions or molecules across the membrane.

Question 30

What are the 2 forms of transporter

Answer 30

• Channels: create a port through the membrane through which molecules, usually ions flow, Can be gated or open
• Carrier proteins: do not create a continuous pore from ECF to ICF. Open to ECF the ICF but never at the same time. Can move larger molecules than channels e.g. glucose

Question 31

What do membrane enzymes do?

Answer 31

Catalyse chemical reaction on the cell membrane

Question 32

Give an example of internal and external enzymes

Answer 32

• External: those found in the small intestine which break down nutrients into smaller subunits,
• Internal: those associated with converting signals carried from receptors into an intracellular response

Question 33

What are the 3 main roles of peripheral membrane proteins?

Answer 33

• Maintain structure of cells by anchoring membrane to intracellular cytoskeleton.
• Attach cells to the extracellular matrix e.g collagen
• Perform signalling functions within cells e.g G proteins

Question 34

What is myelin?

Answer 34

A membrane that serves as an insulator around myelinated nerve fibres and has a low protein content. A major component is lipid

Question 35

What is the typical protein content of plasma membranes of cells other than that of myelinated nerve fibres?

Answer 35

50%

Question 36

What membranes has protein contents of around 75%?

Answer 36

Membranes involved in energy transduction such as the inner membranes of the mitochondria

Question 37

What are membrane carbohydrates linked to proteins and lipids as?

Answer 37

Glycoproteins and glycolipids

Question 38

What role do membrane carbohydrates play?

Answer 38

Self-versus non-self recognition and in the immune system