1.3 membrane proteins

Question 1

what is the plasma membrane made up of, illustrated by the fluid mosaic model?

Answer 1

phospholipids, cholesterol, proteins and carbohydrates

Question 2

which r groups do peripheral proteins contain?

Answer 2

hydrophilic

Question 3

which type of r group is found in integral proteins?

Answer 3

hydrophobic

Question 4

why do peripheral proteins have hydrophilic r groups?

Answer 4

to allow them to bind to the surface if the membrane

Question 5

why do integral proteins have hydrophobic r groups?

Answer 5

to allow for strong hydrophobic interactions that allow the protein to be held within the phospholipid bilayer

Question 6

how does the phospholipid bilayer act as a barrier to ions and most polar molecules?

Answer 6

due to its hydrophobic nature

Question 7

what is the role of transmembrane proteins?

Answer 7

to act as channels/transporters and allow passive transport of substances to take place via facilitated diffusion

Question 8

what are gated channels?

Answer 8

channels that change conformation to allow or prevent diffusion

Question 9

how do gated channels open/close?

Answer 9

by responding to stimuli

Question 10

how are ligand-gated channels controlled?

Answer 10

by the binding of signal molecules

Question 11

how are voltage-gated channels controlled?

Answer 11

by changes in concentrations

Question 12

how do transporter proteins transport solutes?

Answer 12

the protein binds to a substance that is to be transported and undergoes a conformational change that allows the transfer of the solute across the membrane

Question 13

why do transporter proteins alternate between two conformations?

Answer 13

so that the binding site for the solute is exposed to one side of the bilayer, then the next

Question 14

what happens when transporter proteins require energy to bring about conformational change?

Answer 14

the transport becomes active, using energy from the hydrolysis of ATP

Question 15

what is membrane potential?

Answer 15

the electrical potential difference created when there is a difference in electrical charge on the two sides of the membrane

Question 16

what is the electrochemical gradient?

Answer 16

when concentration gradient and membrane potential combine

Question 17

does the electrochemical gradient determine?

Answer 17

the transport of the solute

Question 18

which way does the SPP transport sodium ions?

Answer 18

out of the cell

Question 19

which way does the SPP transport potassium ions?

Answer 19

into the cell

Question 20

what is step 1 in the workings of the SPP?

Answer 20

the transporter protein has a high affinity for sodium ions, therefore binding occurs.

Question 21

what is step 2 in the SPP?

Answer 21

phosphorylation by ATP causes the conformation of the protein to change

Question 22

what is step 3 in the SPP?

Answer 22

the affinity for ions decreases resulting in sodium being released from the cell

Question 23

what is step 4 in the SPP?

Answer 23

potassium ions from outside of the cell bind to the sodium/potassium pump

Question 24

what is step 5 in the SPP?

Answer 24

dephosphorylation occurs which causes the conformation of the protein to change

Question 25

what is step 6 in the SPP?

Answer 25

potassium ions are taken into the cell and affinity returns to the start

Question 26

explain the net charge produced by the SPP

Answer 26

for every 3 Na ions pumped out, only 2 K ions are pumped in. This creates a slightly -ve charge in the cell

Question 27

what is the main function of the SPP?

Answer 27

generation of the sodium ion gradient across the PM for the active transport of glucose in the small intestine (epithelial cells)

Question 28

what does the glucose transporter transport?

Answer 28

both sodium and glucose at the same time and direction

Question 29

describe the concentration gradients involved with the glucose transporter

Answer 29

sodium ions enter down their concentration gradient while glucose goes against its concentration gradient