Cells - Transport Across Membranes: Cell Membranes

Question 1

What is common between all plasma membranes?

Answer 1

Phospholipid bilayer structure

Question 2

Describe the structure of the phospholipid bilayer

Answer 2

Two layers of phospholipids facing each other. Hydrophilic heads point out, attracted by water on both sides. Hydrophobic tails point into the centre of the membrane, repeller by the water.

Question 3

Functions of phospholipids in the membrane

Answer 3

Allow lipid soluble substances to enter and leave the cell.
Prevent water-soluble substances entering and leaving the cell.
Make the membrane flexible and self-sealing.

Question 4

What gives different membranes different properties?

Answer 4

The different substances they contain.

Question 5

What 4 substances to cell-surface membranes contain?

Answer 5

Proteins
Cholesterol
Glycoproteins
Glycolipids

Question 6

Where are proteins in the cell-surface membrane?

Answer 6

They may move freely or be anchored by the cytoskeleton.

Question 7

Which type of proteins move freely in the cell-surface membrane?

Answer 7

Intrinsic proteins

Question 8

Which type of proteins are anchored in the cell -surface membrane by the cytoskeleton?

Answer 8

Extrinsic proteins.

Question 9

How are intrinsic proteins positioned in the phospholipid bilayer?

Answer 9

They span the bilayer

Question 10

Where are extrinsic proteins positioned in the phospholipid bilayer?

Answer 10

They are partially embedded in the inside or outside of the bilayer.

Question 11

Give an example of an intrinsic protein

Answer 11

Transport proteins

Question 12

What are two different types of transport protein?

Answer 12

Channel protein

Carrier protein

Question 13

What do transport proteins do in the phospholipid bilayer?

Answer 13

They control the movement of polar ions/molecules across the membrane.

Question 14

Give 4 functions of proteins in the cell surface membrane.

Answer 14

Structural support
Transport of water-soluble substances across the membrane
Allows active transport across the membrane
Act as receptors allowing cell signalling

Question 15

Where is cholesterol positioned in the cell-surface membrane?

Answer 15

Fits between the fatty acids tails within the phospholipid bilayer.

Question 16

Give 3 functions of cholesterol in the cell-surface membrane.

Answer 16

Reduces lateral movement of other molecules, stabilising the membrane.
Prevents loss of water and dissolved ions.
Regulates fluidity.

Question 17

What are the 3 factors that change membrane fluidity?

Answer 17

Cholesterol
Temperature
Saturated or unsaturated fatty acid tails in the bilayer

Question 18

What are glycoproteins?

Answer 18

Carbohydrate chains attached to extrinsic proteins on the outer surface of the membrane.

Question 19

What are glycolipids?

Answer 19

Carbohydrates covalent oh bonded with lipids on the outer surface of the membrane.

Question 20

What are glycoproteins receptors for?

Answer 20

Hormones and neurotransmitters

Question 21

What are glycolipids receptors for?

Answer 21

Specific chemicals

Question 22

Why do glycoproteins act as antigens?

Answer 22

To allow recognition of ‘self’ by lymphocytes in the immune system.

Question 23

Give 4 functions of glycoproteins and glycolipids in the cell-surface membrane.

Answer 23

Act as recognition sites
Form glycolax on the outer surface
Help cell adhesion to form tissues
Used in cell signalling

Question 24

What is the fluid mosaic model?

Answer 24

The arrangement of the various molecules in the structure of the cell surface membrane.

Question 25

Why is it called the fluid mosaic model?

Answer 25

Fluid- flexible structure, constantly changing shape, phospholipid molecules can move relative to one another.
Mosaic - proteins vary in shape, size and pattern.
Model - representation that works for all current evidence.

Question 26

How does the cell surface membrane control the movement of substances in and out of the cell?

Answer 26

By being selectively permeable

Question 27

Give 3 functions of the cell-surface membrane.

Answer 27

Controls the movement of substances in and out of the cell.
Separates cell contents from external environments, allowing different conditions inside and out.
Cell recognition and signalling.

Question 28

Where is the modification of carbohydrates into glycoproteins and glycolipids carried out?

Answer 28

The Golgi body

Question 29

Give 2 functions of plasma membranes inside cells.

Answer 29

Separates organelle contents from cytoplasm.

Holds components of metabolic pathways in place.

Question 30

Give 4 reasons why most molecules cannot freely diffuse through the cell-surface membrane?

Answer 30

Not soluble in lipids
Too large to pass through channel proteins
Of the same charge as the protein channels
Polar

Question 31

Why cant molecules which are not soluble in lipids freely diffuse through a cell-surface membrane?

Answer 31

They can’t get through the phospholipid bilayer.

Question 32

Why can’t molecules of the same charge as channels proteins freely diffuse through a cell-surface membrane?

Answer 32

They are repealed by the channel proteins.

Question 33

Why can’t polar molecules freely diffuse through a cell-surface membrane?

Answer 33

They can’t pass through the non-polar hydrophobic tails in the phospholipid bilayer.