Lecture 21 C1

Question 1

Describe the fluid mosaic model

Answer 1

Sea of lipids where proteins float like icebergs.

Question 2

What is membrane fluidity

Answer 2

Lipids can move within the plane of the membrane leaflet (1/2). The lipid composition of the leaflet is asymmetric because lipids can rarely move between leaflets.

Question 3

How is membrane fluidity determined

Answer 3

Lipid tail length: the longer the tail, the less fluid.
Number of double bonds in tail: unsaturated lipid makes kinks, more fluid . Amount of cholesterol - more decreases fluidity.

Question 4

what does increased fluidity mean?

Answer 4

Allows more things to pass the lipid barrier to entry or exit of polar substances

Question 5

Describe the structure of the lipid bilayer and the 3 lipids associated with it

Answer 5

8nm thick, phospholipid molecules with non polar lipid facing inwards and polar heads facing outwards. Cholesterol inside the lipid section, and glycolipids on top of the polar part giving cell identity.

Question 6

What is the ratio of lipids to proteins in the cell membrane

Answer 6

1:1

Question 7

What the two classes of membrane proteins

Answer 7

Integral membrane proteins extend into or across the cell membrane so amphipathic. Peripheral protein: attach to inner or outer surface and are easily removed

Question 8

Give 6 examples of the uses of membrane proteins

Answer 8

cell identity markers, channels, linkers (to the intermediate filaments) , enzymes, transporters, receptors.

Question 9

Describe the structure of integral proteins.

Answer 9

The hydrophobic regions consist of non polar amino acids coiled into helices. Hydrophilic ends of the protein interact with the aqueous solution

Question 10

How does selective permeability of the membrane come about

Answer 10

The lipid bilayer barrier to the movement of molecules allows some substances to cross but excludes others. Membrane proteins mediate the transport of substances across the membrane that cannot permeate the bilayer

Question 11

What is the lipid bilayer permeable to

Answer 11

1. non polar, charged molecules: O2, N2, benzene
2. lipid soluble molecules: steroids, fatty acids, some vit.
3. small uncharged polar molecules: water, urea, glycerol, CO2

Question 12

What is the is the lipid bilayer impermeable to

Answer 12

1. large uncharged polar molecules : glucose, amino acids

2. ions : K+, Na+ , Cl-, Ca2+, H+

Question 13

What is the principle of diffusion

Answer 13

Random mixing of particles in a solution as a result of the particles kinetic energy.

Question 14

What factors speed up the rate of diffusion

Answer 14

greater difference in concentration, higher temperature, increase in SA, decrease in diffusion distance, smaller molecule being diffused.

Question 15

What are the physical consequences of diffusion on the cell

Answer 15

size is limited to 20um. The membrane available for diffusion can be increased, membrane thickness can vary.

Question 16

What are the main consequences of having a selectively permeable membrane

Answer 16

concentration gradients,
spatial organisation of chemical and physical processes in the cell,
controlled uptake of nutrients, discharge of waste product and secretion, and development of membrane potential

Question 17

Non charged molecules will diffuse down

Answer 17

their concentration gradient only

Question 18

The net movement of ions across a membrane is influence by what

Answer 18

electrochemical gradient which is the effect of both concentration and electrical gradient.

Question 19

How does the cell make an electrical gradient

Answer 19

Cells use 30% of resting energy to maintain conc and electrical gradients. They mimic capacitors and can separate and store charge. This energy is released when ions can flow

Question 20

what are the three main ion gradients across the cell membrane

Answer 20

Outside the cell is high Na, Low K and High Cl.
Cl- at equilibrium but can go in or out depending on mp.
K+ in electrochemical equilibrium because it goes from high to low but its attracted to negative charge in side

Question 21

What is the charge on the cell membrane

Answer 21

+ charge outside, - charge inside .

Question 22

What is osmosis

Answer 22

net movement of water through a selectively permeable membrane from area of high conc to are of low conc

Question 23

What is the membrane permeability to water (Pw)

Answer 23

Pw= Pd + Pf

Question 24

What is Pd and its properties

Answer 24

movement of water through the lipid bilayer. Small, insensitive to mercury and temperature dependent (lipid fluidity)

Question 25

What is Pf and what is properties

Answer 25

Pf mediated by 9 isoforms of aquaporins- movement of water through channel.
Large, mercury senstive and temp independent.

Question 26

What is osmotic pressure

Answer 26

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

Question 27

What is the difference between osmolarity and tonicity

Answer 27

Osmolarity is the measure of number of dissolved ions/solutes on either side of the semi permeable membrane while tonicity is the effect of intracellular and extracellular osmolarity (having on water movement that effects ) cell volume .

Question 28

A cell in hypertonic solution causes water to move what way

Answer 28

Hypertonic solution -> has more solutes outside cell-> hyperosmotic -> less water outside cell-> water moves out of cell-> crenation

Question 29

A cell in hypotonic solution causes water to move what way

Answer 29

Hypotonic solution-> less solutes outside cell-> hypoosmotic-> more water outside cell-> water moves into cell-> lysis