Introduction to cell membranes (2)

Question 1

Why do red blood cells have a biconcave structure?

Answer 1

To increase their surface area for gas exchange

Question 2

What do optical tweezers show?

Answer 2

Tensile strength of red blood cell membranes

Question 3

What happens to red blood cells in hypertonic, isotonic and hypotonic solutions?

Answer 3

-hypertonic = water leaves cell + cell becomes crenelated (spiky)
-isotonic = no water moves + cell remains round
-hypotonic = water enters cell + cell eventually bursts

Question 4

What are red blood cell ghosts?

Answer 4

Predominantly plasma membrane as the haemoglobin is washed away

Question 5

Why do red blood cells have relatively simple protein compositions?

Answer 5

-they’re terminally differentiated cells
-protein composition is reflective of their function

Question 6

What do mutations in spectrin cause?

Answer 6

Certain types of haemolytic anaemia

Question 7

What do integral membrane proteins do?

Answer 7

-anchor cytoskeleton to plasma membrane
-provide structure to the cell
-allow it to change shape

Question 8

What are key features of biological membranes?

Answer 8

-membranes are asymmetric
-proteins always have the same orientation in the membrane
-lipid composition of each of the 2 halves of the bilayer is different

Question 9

What is the asymmetry of membranes important for?

Answer 9

-blood groups
-coagulation (clot formation)
-cell recognition + clearance

Question 10

What blood groups can individuals have?

Answer 10

-O
-A
-B
-AB

Question 11

What is blood group determined by?

Answer 11

Structure of oligosaccharides attached to sphingomyelin in the red blood cell membrane + to proteins in plasma + other body fluids

Question 12

Which blood group is the universal donor and which is the universal acceptor?

Answer 12

-O = universal donor
-AB = universal acceptor

Question 13

What is coagulation?

Answer 13

-clot formation
-phosphatidylserine on platelets + cell membrane provide nucleation site for coagulation

Question 14

What do macrophage plasma membranes contain and where are they transferred to?

Answer 14

-contain receptors that recognise aminophospholipids
-transferred to outer leaflet of plasma membrane on apoptotic cells

Question 15

What are liposomes?

Answer 15

Phospholipids form spherical structure in aqueous solution

Question 16

What is passive transport?

Answer 16

-solutes move down a concentration gradient
-involves channels or carriers

Question 17

What is active transport?

Answer 17

-solutes move against a concentration so requires energy
-only carriers involved

Question 18

What can active transport be mediated by?

Answer 18

-coupled carrier
-ATP driven pump
-light driven pump

Question 19

What produces the ion concentration difference on either side of the membrane that results in an electrochemical gradient?

Answer 19

Produced through action of ion channels + carriers/pumps

Question 20

Do channels or carriers transport solutes more rapidly and why?

Answer 20

-channels
-carrier proteins directly bind to solute, whereas channels interact very weakly with solute

Question 21

How does passive transport by a carrier occur?

Answer 21

-solute binds to carrier in state A
-carrier converts into state B
-releases solute on other side of membrae

Question 22

What are the types of ion channel?

Answer 22

-voltage gated
-ligand gated with extracellular ligand
-ligand gated with intracellular ligand
-mechanically gated

Question 23

What are the types of carrier-mediated transport?

Answer 23

-uniport
-symport - cotransported ion on same side of transported mol.
-antiport - cotransported ion on opposite side of transported mol.

Question 24

What is the difference in what drives transport across mammalian plasma membrane and bacterial/yeast intracellular membranes?

Answer 24

-mammalian - driven by Na+ gradients
-bacteria/yeast - driven by H+ gradients

Question 25

Describe the transcellular transport of glucose

Answer 25

-moves against conc. grad.
-driven by glucose/Na+ symporter at apical surface - coupled uptake of glucose
-results in high Na+ conc. in cell that prevent symporter working
-Na+ moves out of cell into blood by Na+/K+ pump at basal surface
-high glucose conc. in cell - moves into blood using glucose carrier at basal surface