DW Lecture 4: Lipids, plasma membrane

Question 1

List the most abundant lipids in the plasma membrane.

Answer 1

phospholipids
sphingomyelin
glycolipids
cholesterol

Question 2

Which phospholipids are negatively charged?

Answer 2

phosphatidylserine (PS)

phosphatidylinositol (PI)

Question 3

Which phospholipids are neutral in charge?

Answer 3

phosphatidyl-ethanolamine

Question 4

Which lipids are typically found on the cytosolic side of the bilayer?

Answer 4

PS (unless the cell is undergoing cell death)
PI
phosphatidyl-ethanolamine
cholesterol (found in both)

Question 5

Which lipids are typically found on the extracellular side of the bilayer?

Answer 5

phosphatidylcholine
sphingomyelin
glycolipids
cholesterol (found in both)

Question 6

What are membranes composed of only phospholipids permeable to?

Answer 6

highly: gases and hydrophobic molecules
slightly: small polar molecules
impermeable: large polar molecules and charged species

Question 7

What does increasing the concentration of cholesterol do to the permeability of a membrane?

Answer 7

it decreases permeability to small polar molecules (e.g water)

Question 8

What is passive transport

Answer 8

movement from high concentration to low concentration

including simple diffusion, transport channels, and transport carrier proteins

Question 9

What is active transport

Answer 9

from low concentrations to high concentrations

requires energy and is mediated by pumps

Question 10

What are fatty acids?

Answer 10

carboxylic acids with long hydrocarbon tails

Question 11

What is the difference between saturated and unsaturated fatty acids?

Answer 11

saturated: contain all single bonds between carbons
unsaturated: some double bonds between carbons

Question 12

What are the most abundant glycerophospholipids in the cell membrane?

Answer 12

phosphatidylethanolamine (PE)
phosphatidylcholine (PC)
phosphatidylserine

Question 13

What is unique about the structure of sphingolipids?

Answer 13

they do not contain a phosphate group in the general structure

Question 14

Describe the general structure of sphingolipids.

Answer 14

sphingosine + fatty acid tail + variable group (can contain a phosphate)

Question 15

Describe the structure of cholesterol.

Answer 15

multi-ring structure (steroid nucleus) + hydrocarbon tail + hydroxyl group

Question 16

What is the function of cholesterol in the bilayer?

Answer 16

increases impermeability to small polar molecules (e.g water) due to the hydroxyl group on the steroid nucleus

Question 17

What influences the fluidity of a membrane?

Answer 17

temperature
phospholipid structure
cholesterol

Question 18

How does temperature influence membrane fluidity?

Answer 18

increased temperature increases fluidity by increasing kinetic energy

Question 19

How does the phospholipid structure influence membrane fluidity?

Answer 19

shorter fatty acid tails increase fluidity (less viscous)

unsaturated fatty acids increase fluidity (because the kinked hydrocarbon tails are harder to pack together)

Question 20

How does cholesterol influence membrane fluidity?

Answer 20

stabilizes the membrane at higher temperatures and increases the melting point
prevents clustering of phospholipids at lower temperatures (intercalates between the hydrocarbon tails to increase fluidity)

Question 21

What are the two categories of membrane proteins?

Answer 21

integral (directly inserted into a lipid membrane or covalently bound to other groups that are inserted)
peripheral (associated with the membrane through non-covalent interactions)

Question 22

List teh key molecular characteristics of transmembrane helical proteins.

Answer 22

1. contain predominantly hydrophobic side chains that interact with the lipid bilayer
2. transmembrane residues that face a polar channel or have polar side chains
3. residues in the extracellular space and cytosol often have polar side chains (because they interact with aqueous environments
4. intracellular regions close to the membrane tend to be abundant with positively charged residues