Membranes 3

Question 1

Ion channels

Answer 1

selective and gated

Question 2

2 classes of membrane transport protein

Answer 2

carrier and channel

Question 3

Carrier proteins

Answer 3

small organic molecules eg AAs and sugars
Alternative axis mechanism- don’t have continuous channel through membrane
Substrate binding site one side- when subs binds conformational change and subs released other side
Subs on side with low conc less likely to bind- ensures movement only high to low conc
Energy independent

Question 4

3 types of transport

Answer 4

uniport symport and antiport

Question 5

coupled transport

Answer 5

carried out by symporters and antiporters
transport of 2 different types of molecules interdependent on one another for transport
Use energy released from movement of one ion (Na+/H+ usually) down electrochemical gradient to power import/export of small molecule/different ion

Question 6

Symport

Answer 6

same direction
Move substrates against conc gradient
Have co-transported ion

Question 7

Antiport

Answer 7

opposite direction

Have co-transported ion, also against conc gradient

Question 8

Lactose permease

Answer 8

bacterial membrane protein
Transports lactose and protons same direction
Don’t require direct energy via ATP hydrolysis but do require energy for transport of H+- secondary active transport

Question 9

uniport

Answer 9

transport of single type of molecule down its conc gradient

Question 10

secondary active transport

Answer 10

Use energy stored in electrochemical gradient to transport substances

Question 11

Channel proteins

Answer 11

open/closed

continuous channel through which ions can travel

Question 12

passive vs active

Answer 12

passive doesnt require expenditure of energy but active does

Active for driving solute against conc gradient or for charged molecule, electrochemical gradient

Question 13

Active Na+/K+ antiporter

Answer 13

3 Na+ out, 2 K+ in per hydrolysis of ATP, creates a gradient

Pumping of Na+ out creates Na+ gradient across membrane

Question 14

Active Na+/glucose symporter

Answer 14

Requires sodium gradient across the membrane to co-transport glucose against its conc gradient
Secondary active transport as Na+ gradient generated by active transport

Question 15

What makes electrochemical gradient

Answer 15

conc gradient and membrane potential

Question 16

Ion channels

Answer 16

selective and gated

Gating controlled by conditions inside and outside cell

Question 17

Patch clamp recording

Answer 17

Method for measuring ion channels
small area of membrane removed and seals end of glass capillary
Random- may not contain ion channels
Set up electrical circuit and measure current throughout circuit- see if channels are open/closed, because current only flows when channels open
An electrical device ‘clamps’ electric potential across the membrane at pre-determined value. Inward or outward movement of ions quantified by amount of electrical current needed to maintain mem potential at ‘clamped value’

Question 18

Gating

Answer 18

voltage gated channels respond to change in voltage across membranes
Ligand gated, the ach receptor
Mechanically gated channels in auditory cells eg touch receptors

Question 19

Ion channels in nerve cells

Answer 19

open, closed or inactivated
After short time open during dep., become inactivated and don’t go back to closed state till mem becomes repolarised. Hence can’t open again till back to resting potential

Question 20

Propagation of AP

Answer 20

AP influences neighbouring regions of plasma membrane and is therefore a wave of dep.
AP moves in 1 direction as channels behind it are inactivated

Question 21

At nerve terminals

Answer 21

When AP reaches terminal VGC channels open, Ca enters cell causing fusion of vesicles and release of nt
NTs bind to ligand gated ion channels on post syn membrane

Question 22

Other functions of membrae proteins

Answer 22

Enzyme receptors:
have enzymatic activity altered(often activated) by binding of ligand
Linkers:
cell-cell contact
cell- ECM adhesion (integrins)

Question 23

Simple diffusion

Answer 23

O2, CO2 drugs

Question 24

Facilitated

Answer 24

Glucose, AAs (uniporters)

Question 25

Active transport

Answer 25

Ions, small hydrophilic molecules, lipids

Question 26

Cotransport

Answer 26

Glucose and AAs (symporters), various ions and sucrose (anti)