transport across membranes

Question 1

function of proteins and carbohydrates in the membrane

Answer 1

cell recognition of self cells
extracellular enzyme activities
transport of compounds across

impermeable to polar and charged molecules due to hydrophobic centre
- proteins allow their movement

Question 2

diffusion

Answer 2

net movement of molecules from high to low concentrations
driven by gradient, passive

small polar molecules diffuse through gaps in hydrophobic
uncharged, lipophilic molecules diffuse readily
- large, polar molecules do not diffuse

Question 3

facilitated diffusion

Answer 3

movement of molecules from high to low concentration
passive, driven by gradient

depends on specific proteins

activation energy high for diffusion of hydrophilic molecules
- needs dehydrating and rehydrating on other side
- hydrogen bonds made with solvent

Question 4

how does facilitated diffusion work

Answer 4

activation energy needs to be lowered
done by using transporter proteins

molecule dehydrated (water removed) and rehydrated on other side

protein makes non-covalent interactions that replace hydrogen bonding, allowing pass
protein channels make interactions with solutes to replace hydrogen bonding lost
rehydrated on other side

channel proteins open and close based on stimulus

bind to one side of carrier
change of shape allow molecule to move through

Question 5

active transport

Answer 5

movement of molecules from low to high concentrations
depends on presence of specific proteins
requires energy

primary and secondary

Question 6

primary active transport

Answer 6

direct hydrolysis of ATP provides energy for transport

3 sodium ions and 1 ATP bind to the pump
ATP used to phosphorylate pump
- causes shape change
- delivers sodium ions to other side

ion binding sites open on outside of pump

2 potassium ions pumped out of extracellular side
ions bind and phosphate released
- causes shape change of pump
- potassium delivered to inside

Question 7

secondary active transport

Answer 7

energy doesn’t come directly from ATP
comes from the energy stored in the sodium ion gradient

substance and sodium ions bind and pump changes shape
returned to outside via pump
creates gradient in primary

sodium potassium pump allows an electrochemical gradient to be maintained
- internal has high K and low Na
- external has low K and high Na

Question 8

components of biological membranes

Answer 8

phosphoacyglycerols

sterols (also amphipathic)
- help keep structure
cholesterol in animals
stigmasterol in plants
- increase fluidity of membrane

peripheral and integral proteins

both proteins and lipids can have carbohydrates (polysaccharides) added

Question 9

proteins in membranes

Answer 9

peripheral proteins
- associated inside or outside
- loosely attached
- can covalently link to lipids
- electrostatic interaction
- easily detached, pH alters bonds

integral proteins
- span membrane
- multiple trans membrane helices
- hydrophobic areas allowing them to interact with chains in middle and transerve
- involvement in nutrient transport and signalling

symport protein
pump that transport 2 molecules in the same direction

Question 10

osmosis

Answer 10

process by which a solvent passes across a semi permeable membrane from a solution with a low osmotic pressure to high

osmotic pressure is directly proportional to the molar concentration of all the solutes and ions which cannot pass across membrane

high pressure = many solutes and ions dissolved
low pressure = less solutes dissolved

semi permeable membrane allows movement of solvent but not solutes

solvent moves across membrane to equal osmotic pressure on both side of membrane