(05) Transport Across Cell Membranes

Question 1

define non-mediated transport

Answer 1

does not directly use a transport protein

Question 2

define mediated transport

Answer 2

moves materials across membrane with the help of a transport protein

Question 3

define passive transport

Answer 3

moves substances down conc / electrochem gradients only using kinetic energy

Question 4

define active transport

Answer 4

uses energy to drive substances AGAINST conc / electrochem gradients

Question 5

define vesicular transport

Answer 5

NOT ASSESSED
molecules engulfed in vesicles to be moved across membrane, either by exocytosis (out of cell) or endocytosis (encapsulate and bring into cell)

Question 6

non-mediated transport can only occur via…

Answer 6

passive diffusion across the lipid bilayer
non-polar, hydrophobic molecules
direction depends on conc

Question 7

what is non-mediated transport important for? also give some examples of molecules that are transported in this manner

Answer 7

absorption of nutrients / excretion of wastes

O2, CO2, N2, fatty acids, steroids, small alcohols, ammonia, fat-soluble vitamins

Question 8

what is an ion channel? describe its structure

Answer 8

pathway which shields ions through hydrophobic bilayer

hydrophobic amino acids on outside
water filled pore lined by hydrophilic amino acids

note that ions do not bind to pore, hence rapid

Question 9

what is ionic selectivity and how do ion channels structurally perform this?

Answer 9

only allows certain ions to pass
excludes based on CHARGE and SIZE
determined by the specific amino acids lining the pore

eg. ring of negative charge = ion selectivity filter, does not allow other negatively charged ions like Cl- through
SIZE of filter determines which positive ions can pass

Question 10

what are examples of stimuli for gating of ion channels?

Answer 10

voltage, ligand binding, cell volume (stretch), pH (linked to metabolism), phosphorylation (linked to cell signalling pathways)

Question 11

what is the patch clamp technique?

Answer 11

suck an electrical seal into tip of pipette with a clump of membrane
measure the current of ions that flow through –> ion channel function

Question 12

what do detected current fluctuations in current flowing through a channel represent?

Answer 12

conformational changes in channel structure associated with gating

Question 13

what is the main difference between carrier mediated transport and ion channel transport?

Answer 13

carrier mediated requires the molecule to be transported to be BOUND to the carrier, which undergoes a conformational change to release the molecule on the other side of the membrane

hence it’s a LOT SLOWER