Phospholipids and Membrane Proteins

Question 1

In the plasma membrane, lipid-protein interactions are:

Answer 1

non-covalent

proteins and lipids can often move in bilayer

Question 2

The four major classes of phospholipids:

Answer 2

1. Phosphoglycerides
2. Sphingolipids
3. Glycolipids
4. Sterols

Question 3

Phosphoglycerides:

Answer 3

• derived from 3-carbon glycerol backbone
• 2 fatty acid chains attached to backbone
• three major types

Question 4

Sphingolipids:

Answer 4

• derived from sphingosine backbone
• sphingomyelin is major one

Question 5

Glycolipids:

Answer 5

• often sphingosine backbone
• carbohydrate always on external face

Question 6

Sterols:

Answer 6

• primarily cholesterol

Question 7

What leads to the ability of lipids to assemble into a bilayer?

Answer 7

• the amphipathic structure of lipids
  
  • polar head groups
  • non-polar fatty acid chains

Question 8

Function of lipid-bilayer:

Answer 8

• insulates the cell from the environment and organelles from the cytoplasm and from each other.

Question 9

Amphipathic membrane lipids assemble spontaneously into:

Answer 9

• lipid bilayers and then into liposomes
  
  • energetically favorable = maximizes hydrophobic interactions

Question 10

Basic structure of phosphoglycerides:

Answer 10

• Two fatty acid chains attached to two of the three carbons of glycerol backbone.
• One fatty acid chain non-saturated, leads to kink that opposes dense packing and increases membrane fluidity.

Question 11

What are the three common phosphoglycerides of the cell membrane:

Answer 11

1. phosphatidyl-ethanolamine
2. phosphatidyl-serine
3. phosphatidyl-choline

Question 12

What phosphoglyceride carries a net negative charge?

Answer 12

• phosphatidyl-serine

Question 13

Basic structure and function of cholesterol in plasma membrane:

Answer 13

• Polar molecule with a rigid ring structure.
• Stiffens regions of membrane in its vicinity.
• Aliphatic regions keep phospholipid chains apart.

Question 14

Glycolipids structure:

Answer 14

• Derived from sphingosine with sugars added rather than phosphate.
• Asymmetric – sugar on external face of plasma membrane only.

Question 15

GM1 ganglioside used for entry of:

Answer 15

cholera toxin

Question 16

Sphingosine structure:

Answer 16

• one fatty acid chain
• contains an amide

Question 17

Cholesterol and sphingomyelin (SM) are primarily found in what types of membranes?

Answer 17

• plasma membranes
  
  • very minimal content in internal membranes of organelles

Question 18

Intracellular membranes (organelles) are primarily composed of what types of phospholipids?

Answer 18

• PT-ethanolamine and PT-choline

Question 19

Glycolipids are primarily found in what types of membranes?

Answer 19

• plasma membrane and myelin
  
  • little content in internal membranes

Question 20

Is lipid positioning in the plasma membrane constant?

Answer 20

• No, they are very mobile.
  
  • diffuse laterally
  • flexion
  • rotate
  • occassionally flip-flop

Question 21

Are plasma membrane lipids are symmetrically distributed between the internal and external faces?

Answer 21

• No.

Question 22

The inner leaflet of the plasma membrane primarily consists of what two phospholipids?

Answer 22

• PT-serine
• PT-ethanolamine

Question 23

The outer leaflet of the plasma membrane primarily consists of what three phospholipids?

Answer 23

• sphingolipids
• glycolipids
• PT-choline

Question 24

Cholesterol distribution in the plasma membrane:

Answer 24

• roughly equal between leaflets

Question 25

Lipid rafts are:

Answer 25

• areas of non-random lipid distribution within the inner or outer membrane leaflets of the plasma membrane.
• some lipid rafts can attract specific membrane proteins.

Question 26

Lipid rafts are typically composed of:

Answer 26

• cholesterol and sphingomyelin
  
  • form thicker area of plasma membrane that can sequester subsets of membrane proteins

Question 27

Phosphotidylinositol (PI):

Answer 27

• a minor phospholipid
  
  • PIP3 can serve as a dock for downstream signaling molecules.
  • PIP3 can be cleaved and a part of active signaling.

Question 28

What are the two ways membrane proteins can be associated with a membrane?

Answer 28

• peripheral
• integral

Question 29

Peripheral membrane proteins attach to the membrane via:

Answer 29

• electrostatic charge

Question 30

Integral membrane proteins attach to the membrane via:

Answer 30

• stretches of hydrophobic amino acids through membrane.
  
  • either alpha helix of 15-20 amino acids or a barrel, with hydrophilic amino acids buried.
• lipid covalently attached that can reversibly interact with membrane

Question 31

What kind of membrane proteins are these?

Answer 31

integral

Question 32

What kind of membrane proteins are these?

Answer 32

peripheral

Question 33

Some proteins can be post-translationally bound to:

Answer 33

• membrane lipids that serve as “anchors”
  
  • these lipids then mediate the protein’s association with the membrane
  • reversible and can be regulated

Question 34

Membrane proteins can be immobilized by:

Answer 34

• the underlying cytoskeleton
  
  • can be “anchored” to the internal cytoskeleton of the cell