2.1.5 cell membrane structure

Question 1

define compartmentalisation

Answer 1

formation of membrane bound areas in cells

Question 2

why is compartmentalisation important

Answer 2

allows specific conditions for reactions + protects vital cell components
metabolism normally involves incompatible reactions

Question 3

describe the structure of the cell membrane

Answer 3

made of phospholipid bilayer
hydrophilic phosphate heads
hydrophobic FA tails

Question 4

explain what an intrinsic protein is

Answer 4

transmembrane proteins (embedded in both layers in mem.)
have AA and hydrophobic R groups on surface
= interact w/ hydrophobic core of membrane; keeps them in place

Question 5

explain what an extrinsic protein is

Answer 5

present on one side of bilayer
hydrophilic R groups on the surface
interact w/ phosphate heads or intrinsic proteins
provide mechanical support
form glycoproteins/glycolipids

Question 6

describe the structure + function of channel proteins

Answer 6

intrinsic protein
provide protein channels for diffusion of polar mols + ions down a con. gradient
= fill w/ water; allow soluble ions to diffuse
held in position by hydrophobic membrane + R groups

Question 7

describe the structure + function of carrier proteins

Answer 7

intrinsic protein
allow facilitated diffusion and active transport (down and against a con. gradient)
involves protein changing shape
= large molecules bind to protein
= causes protein to change shape + take mol to other side of membrane
often specific to mol. they transport

Question 8

describe the structure + function of glycoproteins

Answer 8

extrinsic proteins
carbohydrate chains attached to surface
play a role in cell adhesion
are receptors for hormones
allows cell-cell comm.

Question 9

explain how cell signaling works

Answer 9

chemicals bind to receptor = elicit response
» direct or chain of events
i.e receptors for neurotransmitters and receptors for peptide hormones

Question 10

describe the structure + function of glycolipids

Answer 10

extrinsic; cell surface
directly attached to phosphate head
lipids with carbohydrate chains
form antigens
can be recognised by cells of immune system (self or non-self)

Question 11

describe the structure + function of cholesterol

Answer 11

lipid w/ hydrophilic + hydrophobic end
regulates fluidity in membranes
positioned between phospholipid bilayer
interaction between FA and phospholipid heads prevents mem. from being too fluid OR too solid (getting too close + crystallising)

Question 12

why is it important for cholesterol to regulate membrane fluidity

Answer 12

makes mem. less fluid at high temps
= dissolved substances + ions wont leak out
= prevents dehydration or cells bursting

Question 13

describe the permeability of the cell membrane

Answer 13

permeable to small hydrophobic molecules
less permeable to small uncharged polar molecules
slightly permeable to large uncharged polar mols
impermeable to ions + charged molecules

Question 14

explain why the membrane is not permeable to charged molecules

Answer 14

phospholipid bilayer is hydrophobic
= repels charged atoms
= repels polar mols too; diffuse slowly

Question 15

summarise the functions of the cell membrane

Answer 15

compartmentalisation
cell-cell recognition and signalling (antigens, antibodies, hormones, + receptors)
control entry and exit of materials in cells
hold components of some metabolic reac. (proteins have enzymes + co-enzymes)

Question 16

give an example of why enzymes + co-enzymes are needed

Answer 16

oxidative phosphorylation on cristae of mitochondria
= produces ATP