Cell Membrane

Question 1

What is the purpose of membranes?

Answer 1

Controls what enters/exits cell.

Site of chemical reactions.

Cell recognition & Cell signalling.

Question 2

What are the functions of phospholipids in the membrane?

Answer 2

Allows diffusion of LIPID-SOLUBLE substances to leave/enter cell.

Prevents movement of WATER-SOLUBLE substances leaving the cell.

Question 3

Explain why phospholipids form a bilayer in plasma membranes [3 marks]

Answer 3

Contains polar phosphate head - hydrophilic and faces outwards to aqueous environment, interacting w/ water. (1)

Contains non-polar fatty acid tails - hydrophobic so it faces inwards and away from aqueous environment. (1)

Question 4

What is the fluid-mosaic model?

Answer 4

The arrangement of molecules in the cell membrane can be described as the fluid-mosaic model.

Question 5

Why is the cell membrane fluid in the fluid-mosaic model?

Answer 5

1) Phospholipids form a bilayer.
2) These molecules are able to MOVE around so membrane is FLEXIBLE.
3) Membrane is constantly changing SHAPE.

Question 6

Why is the cell membrane mosaic in the fluid-mosaic model?

Answer 6

1) Molecules like proteins, glycolipids, glycoproteins are embedded through membrane.
2) Proteins in membrane vary in SIZE & shape.
3) Creates mosaic pattern.

Question 7

What are the 2 types of proteins? [1 mark]

Answer 7

Intrinsic proteins

Extrinsic proteins

Question 8

What are intrinsic proteins? Give examples.

Answer 8

Connects 1 side of phospholipid bilayer to the other.

E.G.
Channel proteins
Carrier proteins

Question 9

What are extrinsic proteins? Give examples.

Answer 9

Embedded in the surface of phospholipid bilayer.

E.G.
Receptors

Question 10

What are glycoproteins? [3 marks]

Answer 10

A protein attached to a carbohydrate chain on the cell-surface membrane.

FUNCTIONS:

1) Act as RECOGNITION site for hormones, neurotransmitters and other cells.
2) Helps cells ATTACH together to form TISSUES.

Glych sounds like glob, sticky, attaches.

Question 11

What are two functions of cholesterol embedded in the cell membrane? [2 marks]

Answer 11

FUNCTIONS

1) Reduce fluidity and permeability of the cell membrane…to make bilayer stable.

2) Increase rigidity of the cell membrane.

Question 12

What is an oligosaccharide?

Answer 12

Smaller than poly, bigger than di (few carb units)

Question 13

Explain the role of glycolipids in membranes [1 mark]

Answer 13

Cell signalling & Cell recognition

Question 14

Explain the functions of intrinsic and extrinsic proteins in membranes. [2 marks]

Answer 14

EXTRINSIC
> Binding sites for receptors (e.g. hormones)
> Cell signalling
> Bind cells together

INTRINSIC
> Channel proteins - for facilitated diffusion
> Carrier proteins - for facilitated diffusion and active transport.

Question 15

Name and explain 3 factors that affect membrane permeability?

Answer 15

> Temperature =
high temperature denatures membrane proteins - phospholipid molecules have more kinetic energy & move further apart.

> pH =
changes tertiary structure of membrane proteins.

> Use of a solvent =
may dissolve membrane.

Question 16

State Fick’s law [1 mark]

Answer 16

(surface area x difference in concentration) / diffusion distance

Question 17

What’s the difference between carrier and channel proteins? [2 marks]

Answer 17

Carrier proteins…
change tertiary structure in order to transport substances.

Channel proteins…
do not change tertiary structure in order to transport substances.

Question 18

What are the similarities between carrier and channel proteins? [3 marks]

Answer 18

> Transports SPECIFIC substances across membrane.
Made of polypeptides.
Found in cell membrane.
Can be used for facilitated diffusion.
Can allow transport down the concentration gradient - high to low.

Question 19

What is facilitated diffusion? [2 marks]

Answer 19

Net movement of LARGE/POLAR molecules or ions using CHANNEL/CARRIER proteins across the cell membrane proteins from a high to low concentration down the gradient.

Question 20

What’s the difference between simple and facilitated diffusion? [3 marks]

Answer 20

Simple diffusion =
> Transport small/non-polar particles
> Moves through membrane directly.
> Down the concentration gradient.

Facilitated diffusion =
> Transports large/polar particles
> Moves through transport proteins.
> Can go down OR against the concentration gradient.

Question 21

What are the components of a cell membrane?

Answer 21

phospholipid bilayer
channel/carrier proteins
cholesterol
glycolipids
glycoproteins

Question 22

What is the function of channel/carrier proteins?

Answer 22

Transport WATER-SOLUBLE substances across membrane

Since phospholipid membrane prevents water-soluble (polar) substances from being transported

Question 23

How do channel proteins work?

Answer 23

Selectively opens if specific ion binds causing change in shape closing on one side and opening on the other