2. 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

• To separate the internal and external environments of the cell.
• 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 evendistriibution 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/exitingthe 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 extrinsicproteins (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

Gases like oxygen and CO2

• Water
• Lipid-based hormones (steroids) e.g.oestrogen

Question 25

Substances that cannot readily diffuse through the cell-surface membrane are large andpolar molecules andsuch as…

Answer 25

• Glucose
• Ions
• Proteins
• Urea

Question 26

In an investigation about diffusion and plasma membranes (beetroot discs) why would you ensure the temperature remained constant?

Answer 26

so that rate of diffusion remains constant

no change in fluidity of phosopholipids

no denaturation of membrane proteins

Question 27

In an investigation about diffusion and plasma membranes (beetroot discs) why would you ensure the the beetroot discs where shaken?

Answer 27

To ensure all the discs exposed to water/ all discs fully submerged

maintain concentration/diffusion gradient

Question 28

name the type of molecules that can diffuse through the membrane

Answer 28

lipid soluble

small

non-polar

Question 29

during cell fractionation a detergent can be used - why?

Answer 29

cell mebranes made of phospholipids

detergent dissolves membranes

releasing cell contents

Question 30

How does ultracentrifugation work to seprate cell organelles?

Answer 30

spin supernatent at low speed initially

then gradually increase the speed

separating organelles out based on their size/density

Question 31

Membrane structure

Answer 31

•Made from lipids (mainly phospholipids), proteins and carbohydrates
It is about 7nm thick
It is described as a fluid mosaic structure.

Question 32

Fluid?
Mosaic?

Answer 32

FLUID-
Individual phospholipid molecules move relative to each other- gives the membrane a flexible structure
MOSAIC- proteins are scattered in bilayer. They vary in shape, size and pattern- like the tiles in a mosaic

Question 33

Label

Answer 33

Question 34

What does cholesterol do?

Answer 34

Reduces lateral movement of molecules including phospholipidsMake membrane less fluid at high temperaturesPrevent leakage of water and dissolved ions from cellAdd strength to membrane

Question 35

What does cholesterol do and what cell does it help?

Answer 35

Cholesterol also has hydrophobic regions so it creates a further barrier to polar substances moving through the membrane i.e. It restricts movement
Cholesterol helps to maintain the shape of red blood cells

Question 36

Membranes contain proteins which means these…(6 pts)

Answer 36

Can move freely in bilayer and some are attached to the outside of cell or a structure in the cytoplasmMay act as enzymesAct as carriers to transport substances in and out of cellsAct as channel proteins to allow specific ions in and outAct as Receptor proteins for hormonesCan act as antigens and are important in cell recognition

Question 37

Membrane Permeability - Below 0

Answer 37

The phospholipids don’t have much energy. They are packed closely together.
Channel and carrier proteins denature. This increases the permeability of the membrane. Ice crystals may form and pierce the membrane increasing permeability

Question 38

Membrane Permeability - Between 0 and 45

Answer 38

The phospholipids can move around. The membrane is partially permeable. As the temperature increases the phospholipids gain kinetic energy and move more. This increases the permeability of the membrane

Question 39

Membrane Permeability - Above 45

Answer 39

The phospholipid bilayer begins to melt. The membrane becomes more permeable. Proteins denature so they can’t control what enters and leaves the cell

Question 40

Membrane Permeability - Above 45

Answer 40

The phospholipid bilayer begins to melt. The membrane becomes more permeable. Proteins denature so they can’t control what enters and leaves the cell

Question 41

Membrane Permeability - Below 0

Answer 41

The phospholipids don’t have much energy. They are packed closely together.
Channel and carrier proteins denature. This increases the permeability of the membrane. Ice crystals may form and pierce the membrane increasing permeability