Membrane protein function

Question 1

carrier proteins

Answer 1

have a specific solute binding site
undergo conformational changes via alternative access model

Question 2

ion channels

Answer 2

can be open or closed
continuous channel
ion selective and gated (regulated)

Question 3

what do carrier proteins transport

Answer 3

small organic molecules
can transport inorganic ions

Question 4

uniporters

Answer 4

transport a single type of molecule

Question 5

coupled transport

Answer 5

transport of 2 different types of molecules that are interdependent on one another
symport and antiport

Question 6

symport

Answer 6

same direction

Question 7

antiport

Answer 7

opposite directions

Question 8

example of passive transporter

Answer 8

GLUT1 for glucose
carrier protein

Question 9

example of a symporter

Answer 9

lactose permease
transports lactose and protons in the same direction
secondary active transport

Question 10

secondary active transporters

Answer 10

require an ion gradient (a form of stored energy) to transport the solute
ion gradients are generated by primary active transport

Question 11

if an electrochemical gradient has no membrane potential, the rate of movement of ions is only dependent on…

Answer 11

concentration gradient

Question 12

glucose sodium symporter

Answer 12

This requires a sodium gradient across the membrane (ie high sodium outside the cell) in order to co-transport glucose against it’s concentration gradient.

Question 13

Na/K ATPase as an antiporter

Answer 13

transports (pumps) 3 Na ions out of the cell and 2 K ions into the cell for each ATP that is hydrolysed. ATP is the fuel/energy source for the pump. Note the pumping of Na ions out of the cell generates a Na gradient across the membrane. Energy needed as Na+ is being pumped against the concentration and electrochemical gradient

Question 14

bacteriorhodopsin

Answer 14

uses light energy to pump protons across a membrane (to generate a proton gradient).

Question 15

nexium

Answer 15

against heartburn/stomach ulcers
. Inhibits H/K ATPase, thus stops protons (acid) being pumped into digestive tract and therefore reduces acidity

Question 16

patch clamp recording

Answer 16

measures ion channel activity
A small area of membrane seals the end of a capillary. Current only flows when ion channels are open.
Double current=double channels open

Question 17

unidirectionality of action potentials

Answer 17

ion channels inactivate
only close when membrane repolarised
cannot open again until membrane returned to resting potential

Question 18

what happens at nerve terminals

Answer 18

voltage gated Ca2+ channels open and Ca2+ enters the cell causing fusion of vesicles with the plasma membrane and the release of neurotransmitters

Question 19

enzyme linked receptors

Answer 19

receptors that have enzymatic activity altered upon binding of a ligand
eg insulin receptor becomes active upon insulin binding and acts as a tyrosine kinase

Question 20

linkers

Answer 20

cell-cell contacts
cell-extracellular matrix adhesions (integrins)