Topic 2: Cell membrane structure

Question 1

The faulty CFTR protein which causes cystic fibrosis is found in a ______ __________.

Answer 1

cell membrane

Question 2

Describe the structure of a phospholipid

2 points

Answer 2

1. Polar hydrophilic head (soluble in water) made of PHOSPHATE GROUP and GLYCEROL
2. 2 non-polar hydrophobic fatty acid tails (insoluble in water) ATTACHED TO THE GLYCEROL

Question 3

If the phospholipids are added to water they form a __________, a ________or a _______ (water on both sides)

The _______ is favoured, as the two fatty acid tails are too bulky to fit into a _______ .

Answer 3

monolayer

micelle

bilayer

bilayer

micelle

Question 4

Key Summary: Why do phospholipids form {a bilayer/the cell membrane}? (4 points)

Answer 4

1. Fatty acid tails of phospholipids are HYDROPHOBIC so associate with each other and they {repel/orientate} themselves away from water.
2. Hydrophobic tails point towards {the centre of the bilayer/towards each other}.
3. Phosphate heads of phospholipids are HYDROPHILIC so they attract and {interact/associate} with water, on both membrane surfaces.
4. Bilayer arrangement is due to the aqueous environment on both sides of the membrane - cytoplasm inside, tissue fluid outside.

Question 5

(Important properties of membranes)
Membranes are _____ and therefore are flexible.

This allows:
_____ to change shape
_________ to break
_________ to fuse together

Answer 5

fluid

cells

membranes

membranes

Question 6

(Important properties of membranes)
Membranes control the passage of ________ through them.

Another important property of the lipid bilayer is that it is a highly __________ structure – it does not allow molecules to freely pass across it. Only _____ and _____ can easily pass through the bilayer.

This property means that _____ molecules and _____ _____ molecules cannot cross the {bilayer/cell membrane}, without the assistance of _______.

Answer 6

substances

impermeable

water and gases

large

small polar

proteins

Question 7

Key Summary: What are the properties of cell membranes? (2 properties)

Answer 7

1, fluid and therefore flexible

2. selectively permeable

Question 8

List the 6 things found in the fluid mosaic model

Answer 8

1. glycoproteins
2. proteins
3. cholesterol
4. glycolipids
5. channel proteins
6. phospholipid bilayer

Note: Carbohydrate attached to glycoproteins and glycolipids is only found on the outside of the cell – tissue fluid side

Question 9

What are the 2 roles of phospholipids?

Answer 9

1. Spontaneously form the lipid bilayer

2. Move to allow proteins to move in the membrane

Question 10

What are the 2 roles of proteins?

Answer 10

1. Can be RECEPTOR BINDING SITES eg. for hormones

2. Can be ENZYMES (especially on inner membrane)

Question 11

What are the 2 roles of channel proteins?

Answer 11

1. Transport specific molecules PASSIVELY across the membrane
2. Involved in facilitated diffusion

Question 12

What are the 3 roles of carrier proteins?

Answer 12

1. transport a specific {large molecule/polar molecule/ion} across the membrane
2. can be involved in active transport
3. can be involved in facilitated diffusion

Question 13

What are the 2 roles of glycoproteins (protein with attached carbohydrate)?

Answer 13

1. act as RECEPTORS eg. for hormones or neurotransmitters
2. allow CELL TO CELL RECOGNITION for recognising similar and non-self cells (important in immune response and in forming tissues)

Question 14

What is the (1) role of glycolipids? (lipids with attached carbohydrate)

Answer 14

1. act as RECEPTORS e.g. for hormones

Question 15

What is the (1) role of cholesterol in the cell?

Answer 15

1. REGULATES MEMBRANE FLUIDITY

Question 16

Some proteins can ____ in the ‘sea’ of phospholipids, but some are anchored in one position, so are not free to ____.

Answer 16

move

move

Question 17

The parts of the proteins which are exposed to an aqueous
environment (cytoplasm or tissue fluid) on the outside and
inside of the cell membrane, or which line the channel of a channel protein,
are composed of amino acids with _______ _ groups.

Answer 17

hydrophilic R

Question 18

The parts of the proteins which are embedded in the centre of the membrane are composed of amino acids with _________
_ groups.

Answer 18

hydrophobic R

Question 19

_______ proteins are more fully embedded in the cell membrane, whereas _______ proteins are more loosely associated with the membrane.

Answer 19

Intrinsic

extrinsic

Question 20

__________ regulates the FLUIDITY of the membrane, regulating the movement of the phospholipids.

Membrane fluidity is also affected by __________.

Answer 20

Cholesterol

temperature

Question 21

Why is the structure of the cell membrane called fluid mosaic?
(explain why the word “fluid” and why the word “mosaic”)
(2 points)

Answer 21

1. Fluid - because phospholipids are moving in the plane of the membrane which causes proteins to move.
2. Mosaic – due to {proteins/glycoproteins} {randomly inserted/scattered/variety of different ones} throughout {membrane/bilayer}.