Lecture 15 Plasma Membrane

Question 1

What are the lipids in the plasma membrane?

Answer 1

Phospholipids, cholesterol and glycolipids. Phospholipids make up around 75% of the lipids. Lipids can move around within its leaflet but rarely flip-flops to the other side (leaflets are asymmetrical)

Question 1

Describe the plasma membrane composition

Answer 1

Fluid mosaic model, 8 x 10^-9m, 50% lipid : 50% proteins, mostly held together by hydrogen bonds

Question 2

What are the influences on membrane fluidity

Answer 2

More cholesterol decreases fluidity
Longer tails decrease fluidity (kinks)
More double bonds increases fluidity

Question 3

How did they split the plasma into two layers?

Answer 3

Freeze fracture electron microscopy

Question 4

What does amphipathic mean?

Answer 4

Has both a polar and non polar region

Question 5

What are integral and peripheral proteins?

Answer 5

Integral proteins extend into or completely across the membrane
Peripheral proteins are attached to the inner/outer membrane and are easily removed/attached

Question 6

Describe the structure of an integral protein with relation to the membrane?

Answer 6

In hydrophobic region: Non polar amino acids coiled into helices
In hydrophilic region: Polar regions interact with the aqueous solution

Question 7

What are functions of membrane proteins?

Answer 7

Enzyme, Linkers, Receptors, Ion channels, Transport proteins, Cell identity markers

Question 8

What is the membrane permeable to?

Answer 8

Nonpolar uncharged molecule, lipid soluble molecules, small uncharged polar molecules

Question 9

What is the membrane impermeable to?

Answer 9

Large uncharged polar molecules, charged molecules

Question 10

What affects the diffusion of particles in a solution

Answer 10

Depends on the molecules kinetic energy: Thus a higher temperature, smaller sized particles, increased surface area, decreased diffusion distance all increase speed of diffusion

Question 11

What are the physical consequences of diffusion?

Answer 11

Limits cell size to 20um
Cell would increases membrane area, decrease membrane thickness

Question 12

What determines gradients across the cell membrane?

Answer 12

The electrochemical gradient

Question 13

How do membrane potentials mimic capacitors

Answer 13

They can separate and store charge

Question 14

What is the extracellular concentrations of Na+, K+ and Cl-?

Answer 14

High Na+ and Cl-, low K+ in extracellular

Question 15

How much of the energy in a cell is used for maintaining concentration gradients?

Answer 15

around 30%

Question 16

What is osmosis and when does it occur?

Answer 16

It is the net movement of water across a selectively permeable membrane from an area of high water concentration to low water concentration. It occurs when there is a osmotic gradient and the membrane is permeable to water but not certain solutes.

Question 17

What is osmotic pressure?

Answer 17

Pressure applied to a solution to prevent the inward flow of water across a semi-permeable membrane