3.2.3.1 - Cell Membrane Structure and Function

Question 1

All membranes around and within cells (including those surrounding organelles) are called…

Answer 1

plasma membranes

Question 2

What do we call the plasma membrane that surrounds cells?

Answer 2

Cell-surface membrane

Question 3

What is the function of a cell surface membrane?

Answer 3

1. To separate the internal and external environments of the cell.
2. To control the movement of substances in and out of the cell.

Question 4

Name the components of a cell surface membrane.

Answer 4

• Phospholipids
• Proteins (intrinsic and extrinsic)
• Glycoproteins
• Glycolipids
• Cholesterol

Question 5

Phospholipids have polar and non-polar regions. A molecules that exhibits both of these properties is said to be…

Answer 5

Amphipathic

Question 6

What is a polar molecule?

Answer 6

A molecule that does not have an even distriibution of electrons making some regions more negative than others.

Question 7

What is a non-polar molecule?

Answer 7

A moelucle that has an even distribution of electrons, meaning it does not have areas that are more negative than other areas.

Question 8

Phospholipids are made form which 3 molecules?

Answer 8

Phosphate

Glycerol

Fatty acid ‘tails’ x 2

Question 9

Describe the phosphate head of a phospholipid.

Answer 9

• Polar
• Hydrophillic - water loving

Question 10

Describe the fatty acid ‘tails’ of a phospholipid.

Answer 10

• Non-polar
• Hydrophobic - ‘water hating’

Question 11

What are the functions of the phospholipids in the cell membrane?

Answer 11

• Allow lipid-soluble (non-polar) substances to enter/exit the cell.
• Prevent water soluble (polar) substances entering/exiting the cell.
• Makes the membrane flexible and self-sealing.

Question 12

Proteins in a cell membrane can either be __________ or _________.

Answer 12

Intrinsic or extrinsic

Question 13

Which components of the cell-surface membrane are visible in this diagram?

Answer 13

Phospholipid bilayer

Cholesterol molecule (green)

Question 14

Which components of the cell-surface membrane are visible in this diagram?

Answer 14

Phospholipid bilayer

2 x extrinsic proteins (carriers)

Question 15

Which components of the cell-surface membrane are visible in this diagram?

Answer 15

Phospholipid bilayer

Glycolipid molecules x 2

Question 16

Which components of the cell-surface membrane are visible in this diagram?

Answer 16

Phospholipid bilayer

Glycoproteins x 2

Question 17

Which components of the cell-surface membrane are visible in this diagram?

Answer 17

Phospholipid bilayer

Intrinsic proteins x 2 (channel and carrier)

Question 18

What are the funcitons of proteins in the cell membrane?

Answer 18

• Provide structural support
• Act as channels to transport polar molecules (facillitated diffusion)
• Allow active transport (carrier proteins)

Question 19

What is the function of cholesterol in cell-surface membranes?

Answer 19

• Reduces lateral movement of molecules that make up the membrane.
• Acts as a buffer against temp increases/decreases to maintain membrane fluidity.
• Prevents leakage of water and dissolved ions from the cell.

Question 20

What is a glycolipid?

Answer 20

A carbohydrate (polysaccharide) covalently bonded to a lipid.

Question 21

What are the functions of glycolipids?

Answer 21

• Act as cell recognition sites (ABO blood group antigens are glycolipids)
• Maintain stability of cell surface membrane.
• Help cells to attach to one another and form tissues.

Question 22

What is a glycoprotein?

Answer 22

An extrinsic cell surface membrane prtoein with a carbohydrate covalently bonded to it.

Question 23

What are the funcitons of glycoproteins in the cell surface membrane?

Answer 23

• Act as recognition sites (for hormones and neurotransmitters)
• Help cells to attach and form tissues.

Question 24

Substances that can readily diffuse through the cell-surface membrane are small polar molecules and non polar molecules such as…

Answer 24

1. Gases like oxygen and CO₂
2. Water
3. Lipid-based hormones (steroids) e.g. oestrogen

Question 25

Substances that cannot readily diffuse through the cell-surface membrane are large and polar molecules and such as…

Answer 25

1. Glucose
2. Ions
3. Proteins
4. Urea