Cell Processes Lecture 21

Question 1

Functions of the Cell Membrane

Answer 1

acts as an impermeable (to charged ions), selective barrier to the movement of substances in and out of the cell
- isolates cells from external environment

Question 2

The control of substances in/out of cells allows:

Answer 2

• concentration gradients to be maintained
• the spatial organisation of chemical and physical processes within cell
• the controlled uptake of nutrients and discharge of waste products and the secretion of molecules
• the development of membrane potential

Question 3

The structure of the cell membrane can be described as a _____ _____ _____ made up of _____ and _____ which surrounds the _______ of the cell

Answer 3

Fluid mosaic model; phospholipids; proteins; cytoplasm

Question 4

What is the width of the average cell membrane

Answer 4

8nm

Question 5

The phospholipids in the bilayer contain: and are

Answer 5

Hydrophobic tails (which make up the hydrophobic core) and Hydrophilic heads. Amphipathic

Question 6

What substances are scattered among the double row of phospholipid molecules

Answer 6

Cholesterol and glycolipids

Question 7

Membrane Fluidity is determined by:

Answer 7

• number of double bonds (the more the higher the fluidity)
• amount of cholesterol (the more the lower the fluidity)
• lipid tail length (the longer the tail the less fluid the membrane)

Question 8

Two types of membrane proteins

Answer 8

Integral proteins and Peripheral Proteins

Question 9

Integral Proteins

Answer 9

extend into or completely across cell membrane (transmembrane), are aphipathic and consists of non-polar amino acids coiled into alpha helices and hydrophilic ends which interact with aqueous solution

Question 10

Peripheral Proteins

Answer 10

Attached to either the inner or outer surface of the cell membrane and are easily removed from it

Question 11

Functions of membrane proteins

Answer 11

• Receptor Proteins
• Cell Identity Markers
• Linkers
• Enzymes
• Ion Channels
• Transporter Proteins

Question 12

Permeability is governed by….

Answer 12

…. the laws of diffusion

Question 13

Permeability depends on molecules’:

Answer 13

• size
• charge
• lipid solubility

Question 14

Membrane proteins function in permeability

Answer 14

Mediate the transport of substances across the membrane which can’t permeate the hydrophobic core of the lipid bilayer

Question 15

The membrane is permeable to:

Answer 15

• non polar, uncharged molecules e.g. glucose, amino acids
• lipid-soluble molecules e.g. steroids, fatty acids and some vitamins
• small uncharged polar molecules e.g. water, urea, glycerol and CO2

Question 16

The membrane is impermeable to:

Answer 16

• large uncharged polar molecules e.g. glucose, amino acids

- ions e.g. Na+, K+, Cl-, Ca2+ and H+

Question 17

Principle of Diffusion

Answer 17

random mixing of particles in a solution as a result of the particles Ek from an area of high to low concentation

Question 18

Factors that increase rate of diffusion

Answer 18

• greater difference between concentrations
• higher temperature
• smaller size of diffusing substance
• increasing surface area
• smaller diffusion distance

Question 19

Concentration Gradient

Answer 19

non charged molecules will diffuse down their concentration gradients

Question 20

Electrical Gradient

Answer 20

ions will be influenced by membrane potential in addition to their concentration gradient

Question 21

The combination of these two which ultimately influences movement of ions

Answer 21

Electrochemical gradient

Question 22

What is the size limit that the rate of diffusion sets

Answer 22

20 micrometres

Question 23

What percentage of resting energy is used to maintain the gradients

Answer 23

~ 30%

Question 24

These gradients represent ____ ____

Answer 24

stored energy

Question 25

Osmosis is

Answer 25

the net movement of water through a selectively permeable membrane from an area of higher water concentration or low solute concentration to an area of low water concentration or high solute concentration

Question 26

Osmotic pressures is

Answer 26

the pressure applied by a solution to prevent inward flow of water across a semi permeable membrane

Question 27

Pw =

Answer 27

Pd + Pf where Pd is permeability through lipid bilayer and Pf is permeability through water channel

Question 28

Properties: through bilayer

Answer 28

- small - mercury insensitive - temperature dependent

Question 29

Properties: through water channel

Answer 29

- large - mercury insensitive - temperature independent

Question 30

Pf is mediated by

Answer 30

aquaporins (isoforms)

Question 31

When comparing a solution to a reference solution it is isosmotic if

Answer 31

the osmolarity is the same

Question 32

When comparing a solution to a reference solution it is hyposmotic if

Answer 32

the solution has a lower osmolarity

Question 33

When comparing a solution to a reference solution it is hyperosmotic if

Answer 33

the solution has a higher osmolarity

Question 34

The concentration of body fluids has an osmolarity of

Answer 34

280 Osmols

Question 35

Tonicity is

Answer 35

the effect a solution has on cell volume

Question 36

Tonicity depends

Answer 36

on the membrane permeability of the solute

Question 37

A solution is isotonic if

Answer 37

there is no change in cell volume

Question 38

A solution is hypotonic if

Answer 38

it causes cell swelling and eventually cell lysis

Question 39

A solution is hypertonic if

Answer 39

it causes cell shrinkage