4.1 Structure of cell surface membrane

Question 1

3 cell-surface membrane functions

Answer 1

plasma membrane that…
1. surrounds cells and forms boundary between cell cytoplasm and external environment
2. controls movement of substances in and out of cell
3. allows different conditions to be established inside and outside of cell

Question 2

3 functions of phospholipids in membrane

Answer 2

1. allow lipid-soluble substances to enter and leave the cell
2. prevent water-soluble substances entering and leaving cell
3. make membranes flexible and self-sealing

Question 3

phospholipid in cell-surface membrane

Answer 3

form bilayer
hydrophyllic heads point to outside of csm- attracted to water on both sides
hydrophobic tails point to centre of csm- repelled by water on both sides

Question 4

proteins in surface of bilayer

Answer 4

never extend fully across it
act to give mechanical support to membrane
cell receptors for molecules such as hormones

Question 5

proteins spanning phospholipid bilayer

Answer 5

protein channels- water filled tubes that allow water-soluble ions to diffuse across

carrier proteins- bind to ions or molecules(e.g. glucose or amino acids) then change shape in order to move them across membrane

Question 6

6 functions of proteins in csm

Answer 6

1. provide structural support
2. act as channels transporting water soluble substances across membrane
3. allow active transport across membrane through carrier proteins
4. form cell-surface receptors for identifying cells
5. help cells adhere together
6. act as receptors

Question 7

3 functions of cholesterol in phospholipid bilayer

Answer 7

1. reduce lateral movement of other molecules(including phospholipids)
2. make membranes less fluid at high temps
3. prevent leakage of water and dissolved ions from cell(hydrophobic)

Question 8

cholesterol molecules

Answer 8

add strength to membrane
very hydrophobic
pull together fatty acid tails of phospholipid, limiting movement without making too rigid

Question 9

3 functions of glycolipids

Answer 9

1. act as recognition sites
2. help maintain stability of membrane
3. helps cells attach to one another and so form tissues

Question 10

glycolipids

Answer 10

carbohydrate covalently bonded with lipid
carb extends from phospholipid into water environment outside cell
- acts as cs-receptor for specific chemicals

Question 11

glycoprotein

Answer 11

carb chains are attached to extrinsic proteins on outer surface of cell membrane
- cs receptors for hormones and neurotransmitters

Question 12

3 functions of glycoproteins in membrane

Answer 12

1. act as recognition sites
2. help cells attach to one another and so form tissues
3. allow cells to recognise one another e.g. lymphocytes recognise organisms own cells

Question 13

4 reasons molecules don’t freely diffuse across csm

Answer 13

1. not soluble in lipids and therefore cannot pass through phospholipid layer
2. too large to pass through channels in membrane
3. of the same charge as protein channel charge so they are repelled- even if small enough
4. electrically charged(polar) so have difficulty passing through non-polar hydrophobic tails in phospholipid bilayer

Question 14

fluid mosiac model

Answer 14

the way molecules are combined into structure of csm

fluid- individual phospholipid molecules can move relative to one another, which gives membrane flexible structure that is constantly changing shape

mosiac- proteins embedded in phospholipid bilayer vary in shape, size and pattern