Chapter 10

Question 1

What was the first evidence of plasma membrane?

Answer 1

Studies of mammalian red blood cell plasma membrane showed the lipid bilayer and gave a membrane to study

Question 2

What is the fluid mosaic model of membrane structure

Answer 2

Proteins afloat in a sea of lipids

Slide 6

Question 3

What are peripheral and integral membrane proteins?

Answer 3

Peripheral- proteins that dissociate from the membrane following treatments with polar reagents, such as solutions of extreme pH or high salt concentration that don’t disrupt the bilayer
Integral- can be released only by experimental treatments like amphipathic detergents that disrupt the phospholipid bilayer (permanently in membrane)

Question 4

Can proteins move within phospholipids?

Answer 4

Yes they can move laterally with some restrictions

Example on slide 9

Question 5

What are the 4 important restrictions to mobility of plasma membrane proteins?

Answer 5

1. They can’t move back and forth spontaneously between inner and outer leaflets of the membrane, nor can they reverse their orientation across a membrane
2. Associating with cytoskeletal elements may anchor regions of membranes to a defined location which helps determine shape (slide 11 example)
3. Lipid rafts
4. Separation of basolateral and apical domains of some polarized epithelial cells

Question 6

What is glycophorin?

Answer 6

Associated with cytoskeleton at actin/spectrin junctions on slide 11 protein 4.1

Question 7

What are lipid rafts?

Answer 7

Clusters of cholesterol, sphingomyelin, and glycolipids
Form semisolid patches of membrane
Different integral membrane proteins involved in signalling, etc. are localized within lipid rafts
They create specialized functional domains in plasma membrane
Slide 12

Question 8

Study the layout of the epithelial cell on slide 13

Answer 8

Okay

Question 9

What are intestinal epithelial cells called a polarized cell?

Answer 9

Refers to a cell that has very different structural and functional faces at opposite ends of the cell

NOT refer to any charge differential

Question 10

What is passive diffusion?

Answer 10

Unassisted, direct movement of membrane-permeable molecules across the membrane along a concentration gradient
Slide 17

Question 11

What is facilitated diffusion?

What are the two proteins involved?

Answer 11

Assisted transport for molecules that are not soluble in bilayer
Carrier proteins bind molecules and transport them across membrane (conformational protein change)
Channel proteins (ion channels) open pores through membrane allowing free diffusion of any molecule that’s right size and charge
(Aqueporins- water channel proteins and ion channels- selected ions down an electrochemical gradient)

Question 12

What is the passive glucose transporter?

Answer 12

Conformational changes on glucose molecule are reversible so glucose can move across membrane in either direction
Most cells move inward since low intracellular glucose concentration
Glucose generating cells like liver, basolateral domain of intestinal epithelial cells have outward movement since they have high intracellular glucose concentrations

Slide 19

Question 13

How does a gated ion channel work? (Slide 21)

Answer 13

Rapid movement of ions across channel
Highly selective
Most are gated to allow free opening and closing
Ligand gated and voltage gated

Question 14

What is active transport?

What are ion pumps?

Answer 14

Process by which energy is provided by another coupled reaction and used to drive the uphill transport of molecules across the plasma membrane in an unfavourable direction

Ion pumps are responsible for maintaining gradients of ions across the plasma membrane and provide important examples of active transport driven by ATP hydrolysis

Question 15

What are the typical ion gradient trends in the mammalian cell for Na, K, and Cl?

Answer 15

Na+ is greater outside cell than inside
K+ is is greater inside cell than outside
Cl- is greater outside cell than inside
Slide 24

Question 16

What is the sodium/potassium pump?

Answer 16

Example of active transport that establishes gradient of sodium and potassium ions across plasma membrane of different cell types
2K+ in
3Na+ out
Slide 25

Question 17

What is symport and antiport in active transport?

Answer 17

When molecules are driven across membrane by coupled transport of a second molecule in the energetically favourable way
Symport- both molecules transported in same direction
Antiport- molecules transported in opposite directions across membrane

Question 18

Can glucose be transported using both active and passive transport?

Answer 18

Yes

Slide 27-28

Question 19

What is endocytosis?

What are 3 types?

Answer 19

Material to be internalized is surrounded by an area of the plasma membrane which then buds iff inside the cell to form a vesicle containing the infested material
Pinocytosis- uptake of fluids or macromolecules in small vesicles
Receptor-mediated endocytosis- relies on specific cell surface receptors that recognize molecules to be taken up
Phagocytosis- ingestion of large particles like bacteria

Question 20

What is the low density lipoprotein particle (LDL)?

Answer 20

Cholesterol transported through blood stream to target cells
Cholesterol esters in core
Surrounded by phospholipids and cholesterol
One molecule of ApoB protein on surface
slide 31

Question 21

What is familial hypercholesterolemia?

Answer 21

High levels of circulating serum cholesterol which gives high incidence of heart attacks at early age
Cause-mutations in LDL that prevent binding of LDL to receptor it prevent localization of LDL receptor over coated pits

Uptake of LDL particles by receptor mediated endocytosis and sorting through endosomes slide 32-33