crossing membranes

Question 1

why is it important that lipid bilayers are impermeable to many molecules?

Answer 1

so the cell can control what goes in & out by protein channels

Question 2

what is osmosis

Answer 2

flow of water from high water concentration to low water concentration through semi permeable membrane

Question 3

what is the importance of aquaporin

Answer 3

they are integral membrane proteins involved in transport of water between cells; kidney for water reabsorption

Question 4

name the 4 types of channels/transporters found in cell membranes

Answer 4

uniporter, symporter, antiporter, ATP powered pumps

Question 5

what uniporter is associated with glucose transport out of the epithelial cells of small intestine

Answer 5

GLUT2

Question 6

Describe the functions of the 3 transporters involved in glucose uptake to epithelial cells

Answer 6

Na+/glucose symporter: glucose imported into cell
ATPase pump: pumps Na+ out to create gradient for glucose import
Uniporter: glut2 catalyses diffusion of glucose out of cell

Question 7

Explain the mechanism and importance of glucose transport by glut4

Answer 7

Glut 4 is stored in secretory vesicles and is released via exocytosis. This happens when insulin binds to receptor. Glut 4 transporters are inserted into the membrane and allow glucose to enter the cell. This reduces blood glucose levels

Question 8

What are symporters

Answer 8

Transporters that couple the movement of 2 molecules in the same direction

Question 9

what are antiporters

Answer 9

transporters that couple the movement of 2 molecules in opposite directions

Question 10

why is co-transport important

Answer 10

favourable movement down concentration gradient drives unfavourable movement against concentration gradient

Question 11

How is glucose transported against the concentration gradient in the small intestine

Answer 11

symporter is used, 2 Na+ transported down concentration gradient and this drives 1 glucose into the cell against concentration gradient

Question 12

what is active transport

Answer 12

movement against the concentration gradient driven by ATP hydrolysis

Question 13

what drives conformational changes in the K+/Na+ pump?

Answer 13

phosphorylation/dephosphorylation

Question 14

what are the 2 types of ion channels?

Answer 14

leakage channels & gated channels

Question 15

what are the 3 ways gated ion channels work?

Answer 15

chemically gated, mechanically gated & voltage gated

Question 16

how do chemically gated ion channels work

Answer 16

phosphorylation/binding of ligands

Question 17

what are the 3 possible functional states for a gated ion channel

Answer 17

open (active), closed (resting), inactive (refractory)

Question 18

what is the importance of the nuclear envelope

Answer 18

mediates nuclear protein transport into nucleus and mRNA transport to the cytoplasm