Week2 Plasma Membrane Module

Question 1

What are the four functions of the plasma membrane

Answer 1

1. compartmentalize the cell 2. receives information 3. import/exports molecules 4. Enables movement and expansion of the cell

Question 2

How does the lipid bilayer appear under an electron microsocpe?

Answer 2

Tri-laminar apearance (three layers)

Question 3

What is the general structure of phospholipids?

Answer 3

2 hydrophobic FA tails connected to a glycerol molecule. The glycerol has an attached phosphate. The phosphate is attached to a variable group (choline, ehtanolamine, serine…)

Question 4

What are the four major types of phospholipids found in the plasma membrane? What is the minor one (by mass)?

Answer 4

Posphatidyl-ethanolamine, phosphatidylserine, phosphatidylcholine, sphingomyelin (FAs connected to sphingosine instead of glycerol) Minor one is phosphatidylinositol

Question 5

Phosphatidylserine, where is it found? Charge?

Answer 5

Negative charge found in inner monolayer of membrane

Question 6

Where is phosphatidylcholine primarily found?

Answer 6

major lipid of outer monolayer of plasma membrane

Question 7

where is Phosphatidylinositol found? charge? role?

Answer 7

inner leaflet, negative charge, important in cell signaling

Question 8

Where is cholesterol found in the plasma membrane? Role?

Answer 8

Cholesterol is found evenly distributed throughout the plasma membrane especially between gaps created by cis-bonds in FA tails. Cholesterol is also a major component of lipid rafts. Role: stiffens membrane and makes it less permeable.

Question 9

Glycolipids: what are they? where are they found in the PM? Fxn?

Answer 9

Lipids that contain sugar molecules. Found ONLY in the outer monolayer of the PM. play a role in recognition sites (responsible for A, B and O blood type)

Question 10

How does the charge of the inner leaflet of the membrane compare to the charge of the outer leaflet of the PM membrane?

Answer 10

the inner leaflet is more negative due to the presence of net negative phospholipids (PI, PS)

Question 11

What can diffuse through the PM? why?

Answer 11

Small hydrophobic molecules and small uncharged polar molecules can diffuse. This is because the PM is a hydrophobic barrier where only small non-charged molecules can pass.

Question 12

Categorize the following molecules as diffusable through the PM or not diffusable: H+, Na+, amino acids, glucose, water, glycerol, CO2, O2

Answer 12

Diffusable: CO2, O2, water and glycerol (small uncharged polar) Not: H+, Na+ (ions), amino acids, glucose (large polar)

Question 13

What are lipid rafts? Composition?

Answer 13

microdomains within the PM with specialized function. contain cholesterol and glycopsphingolipids

Question 14

What are the four types (functional categories) of proteins within the PM?

Answer 14

Transporters, anchors, receptors, enzymes

Question 15

What are the four types of associations proteins can have with the PM?

Answer 15

transmembrane, membrane associated, lipid-linked, protein attached

Question 16

What are integral membrane proteins? what three types of association classify as integral? how do you isolate integral membrane proteins?

Answer 16

proteins that span or are covalently attached to the PM. Includes transmembrane proteins, membrane associated proteins, and lipid-linked proteins. Can only be isolated by disrupting membrane with a strong detergent.

Question 17

What are peripheral membrane proteins? what type association classifies as peripheral? How can they be isolated

Answer 17

Proteins not directly attached to the PM (non-covalent association). Includes protein attached proteins.

Question 18

Describe transmembrane proteins. what class of proteins do they belong to? what can be said about their phobicity?

Answer 18

type of integral membrane protein that spans the entire length of the membrane. amphipathic: hydrophobic residues reside in the membrane and hydrophilic residues reside outside the membrane.

Question 19

Transmembrane proteins typically adopt what structure in the transmembrane region? why?

Answer 19

alpha-helix. this ensures that hydrophobic residues are facing the lipids and the hydrophilic polypeptide backbone is on the interior of the helix

Question 20

What is a hydrophilic pore? how is it formed?

Answer 20

a hydrophilic channel through the PM. formed by multiple amphipathic alpha helices. Less commonly beta sheets can coil into cylinders (see in mitochondria)

Question 21

Lipid-linked proteins: how are they attached to PM? Function? (3)

Answer 21

covalently bound to lipids in the membrane. This secures hydrophilic proteins to the PM. Functions in cell growth, differentiation, and morphology

Question 22

What are 4 ways in which lateral diffusion within a membrane can be restricted?

Answer 22

1. binding of membrane proteins to other proteins within the cell 2. binding of membrane proteins to ECM 3. binding of membrane proteins to another cell 4. barriers within the PM that prevent diffusion

Question 23

What is the cell cortex? What are the major players in RBCs?

Answer 23

the meshwork of fibrous proteins on the inside of a cell that stabilize the PM. Spectrin and Ankyrin are major players of RBCs.

Question 24

Glycoproteins? Abundance? Where are sugars attached (extracellular domain or intracellular domain)

Answer 24

Proteins with sugars attached. most proteins are glycosylated. sugars attached to extracellular domain of proteins.

Question 25

Glycocalyx: waht is it? role? (3)

Answer 25

the outer later of PM made by sugars. cell-cell recognition, lubrication (helps cells move through capillary), protection from mechanical damage.

Question 26

What type of protein is this?

Answer 26

Transmembrane Protein

Question 27

What type of protein is this?

Answer 27

Membrane associated

Question 28

what type of membrane protein is this?

Answer 28

Lipid linked

Question 29

what type of membrane protein is this?

Answer 29

Protein attached