1.3 Membrane Proteins

Question 1

what do regions of hydrophobic R groups allow

Answer 1

strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer

Question 2

what are the different types of membrane proteins

Answer 2

integral and peripheral

Question 3

what do integral membrane proteins interact with

Answer 3

they interact intensively with the hydrophobic region of membrane phospholipids

Question 4

what are integral proteins

Answer 4

transmembrane proteins

Question 5

what do peripheral membrane proteins have

Answer 5

hydrophilic R groups on their surface and are bound to the surface of membranes, by ionic and hydrogen bond interactions

Question 6

what do peripheral membrane proteins interact with

Answer 6

they interact with the surface of integral membrane proteins

Question 7

what is the phospholipid bilayer

Answer 7

a barrier to ions and most uncharged polar molecules

Question 8

how do small molecules pass through the bilayer

Answer 8

small molecules such as oxygen and carbon dioxide pass through the bilayer by simple diffusion

Question 9

what is facilitated diffusion

Answer 9

the passive transport of substances across the membrane through specific transmembrane proteins

Question 10

what do cells have to perform specialised functions

Answer 10

different cell types have different channels and transporter proteins

Question 11

most channel proteins in animal and plant cells are

Answer 11

highly selective

Question 12

what are channels

Answer 12

multi-subunit proteins with the subunit arranged to form water-filled pores that extend across the membrane

Question 13

what do channels have to prevent diffusion

Answer 13

some channel proteins are gated and change conformation

Question 14

what are the different types of channel protiens

Answer 14

ligand-gated

voltage-gated

Question 15

what are ligand-gated channels controlled by

Answer 15

the binding of signal molecules

Question 16

what are voltage-gated channels controlled by

Answer 16

changes in ion concentration

Question 17

what are the different types of proteins involved in transporting substances

Answer 17

channel proteins (facilitated diffusion (passive))
transporter proteins (facilitated diffusion (passive))
protein pumps

Question 18

why do transporter proteins bind to the specific substance

Answer 18

to be transported and undergo a conformational change to transfer the solute across the membrane

Question 19

why do transporters alternate between two conformations

Answer 19

so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other

Question 20

what does active transport use

Answer 20

pump proteins that transfer substances across the membrane against their concentration gradient

Question 21

pumps that mediate active transport are

Answer 21

transporter proteins coupled to an energy source

Question 22

what is required for active transport

Answer 22

a source of metabolic energy

Question 23

why do some active transport proteins hydrolyse ATP directly

Answer 23

to provide the energy for the conformational change required to move substances across the membrane

Question 24

what hydrolyses ATP

Answer 24

ATPases

Question 25

what determines the transport of the solute for a solute carrying a net charge

Answer 25

the concentration gradient and the electrical potential difference combine to form the electrochemical gradient that determines the transport of the solute

Question 26

how is a membrane potential created

Answer 26

(an electrical potential difference) when there is a difference in electrical charge on the two sides of the membrane

Question 27

what do ion pumps use energy for

Answer 27

ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients

Question 28

how does the sodium-potassium pump transport ions

Answer 28

transports ions against a steep concentration gradient using energy directly from ATP hydrolysis

Question 29

what does a sodium-potassium pump transport

Answer 29

actively transport sodium ions out of the cell and potassium ions into the cell

Question 30

what are the stages that the sodium-potassium pump goes through

Answer 30

high affinity for sodium ions inside the cell
binding occurs
phosphorylation by ATP
conformation changes
affinity for sodium decreases 
sodium ions released outside of the cell
potassium ions bind outside of the cell
dephosphorylation 
conformation changes
potassium ions taken into cell
affinity returns to start

Question 31

how many ions are transported through the cell membrane

Answer 31

for each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell.
this establishes both concentration gradients and an electrical gradient

Question 32

why is the sodium-potassium pump important

Answer 32

it is found in most animal cells and accounts for a high proportion of the basal metabolic rate in many organisms

Question 33

what does the sodium gradient in the small intestine lead to

Answer 33

the sodium gradient created by the sodium-potassium pump drives the active transport of glucose

Question 34

what happens with the sodium-potassium pump in intestinal epithelial cells

Answer 34

the sodium-potassium pump generates a sodium ion gradient across the plasma membrane

Question 35

what is the glucose transporter responsible for

Answer 35

the glucose symport transports sodium ions and glucose at the same time and in the same direction

Question 36

how are sodium ions and glucose transported in the concentration gradient

Answer 36

sodium ions enter the cell down their concentration gradient, the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient