Membranes and membrane proteins self-study

Question 1

Which type of membrane has the most protein? The most lipid?

Answer 1

Inner mitochondrial membrane has the most protein. Myelin has the most lipid.

Question 2

2 major lipid components in eukaryotic cell membranes

Answer 2

1. Glycerophopholipids (phosphoglycerids) 2. Sphingophospholipids (sphingolipid containing phosphate)

Question 3

Gylcerophospholipids

Answer 3

Most abundant lipids of membrane and increase fluidity. Glycerol backbone to which phophoric acid is esterified at alpha C and 2 long chain fatty acids esterified to remaining C atoms. Attachment of phosphate to alpha C makes glycerol symmetric. 2 fatty acyl groups esterified to C1 and C2 of glycerol. 2 long fatty acid chains (carboxylic acids with long chain hydrocarbon side groups) esterified to the 2 remaining C atoms of glycerol (tails)

Question 4

Saturated vs unsaturated fatty acids

Answer 4

Saturated contains no double bonds (flexible, usually on C1) and unsaturated (usually on C2) contains one or more double bonds

Question 5

Fatty acid double bonds

Answer 5

Usually cis which puts rigid bend in hydrocarbon chain of unsaturated fatty acids, interfering with packing and reduces van der Waals forces and melting points

Question 6

Impact of straight fatty acid chains on membrane fluidity

Answer 6

Saturated and unsaturated trans fatty acids decrease fluidity (increase rigidity)

Question 7

Impact of kinked fatty acid chains on membrane fluidity

Answer 7

Unsaturated cis fatty acids increase fluidity (decrease rigidity). Create pockets containing water and small ions.

Question 8

Amphipathic

Answer 8

Contain both hydrophilic and hydrophobic components

Question 9

Micelles

Answer 9

Formed by amphipathic compounds put in aqueous solutions, thermodynamically favorable

Question 10

5 major groups attached by phosphodiester bridge to glycerol

Answer 10

1. Choline 2. Ethanolamine 3. Serine 4. Glycerol 5. Inositol

Question 11

2 most common glycerol-phospholipids in membranes

Answer 11

1. Phosphatidylethanolamine (cephalin) 2. Phosphatidylcholine (lecithin) Have polar heads with no net electric charge at neutral pH

Question 12

3 membrane molecules with polar heads with negative charge

Answer 12

1. Phosphatidylinositol 2. Phosphatidylserine 3. Cardiolipin

Question 13

Sphingolipids

Answer 13

Amino alcohols sphigosine and dihydrosphingosine are backbones.

Question 14

Ceramide

Answer 14

Sphingosine with saturated or unsaturated long chain fatty acyl group in amide linkage on the amino group. 2 nonpolar tails.

Question 15

Sphingomyelin

Answer 15

Phosphorylcholine + Ceramide Most abundant sphingolipid in mammalian tissues. Predominantly on outer leaflet.

Question 16

Cholesterol in membranes

Answer 16

Compact, rigid hydrophobic molecule. More membrane cholesterol means decreased membrane fluidity. Reduces fluidity near membrane surface.

Question 17

What membrane has the highest concentration of neutral lipids and sphingolipids?

Answer 17

Plasma membranes

Question 18

Intracellular membrane lipid makeup

Answer 18

Primarily glycophospholipids with little sphingolipids or cholesterol

Question 19

Cardiolipin

Answer 19

Found nearly exclusively in the inner mitochondrial membrane

Question 20

Lipid bilayer fluidity

Answer 20

Individual molecules can move rapidly in their own monolayer but do not readily exchange with adjoining layer (flip-flop)

Question 21

Lipid bilayer permeability

Answer 21

Essentially impermeable to nonlipid and charged molecules but not to neutral hydrophobic molecules

Question 22

Membrane protein movement

Answer 22

Move laterally don’t easily flip-flop. Slower than lipids. May be restricted by other membrane proteins they may be attached to (microtubles or microfilaments)

Question 23

Asymmetric distribution of proteins in membranes

Answer 23

Sphingomyelin predominantly on outer leaflet. Phosphatidylethanolamine mostly on inner leaflet. Cholesterol evenly distributed on both sides.

Question 24

Integral membrane proteins

Answer 24

Sequences rich in hydrophobic amino acids which interact with the hydrophobic hydrocarbons of the lipids

Question 25

Peripheral membrane proteins

Answer 25

Located on the cell surface

Question 26

4 functions of membrane proteins

Answer 26

1. Mediators of transmembrane movement of charged/uncharged molecules 2. Receptors for binding hormones/growth factors 3. Enzymes involved in signal transduction 4. Structural to maintain shape

Question 27

Where is membrane fluidity the greatest?

Answer 27

In the middle (at the ends of the hydrocarbon chains)

Question 28

Ca2+ ions and fluidity

Answer 28

Decrease fluidity because of interaction with negatvely charged phospholipids

Question 29

Lipid rafts

Answer 29

Microdomains which move as a unit within outer and inner leaflet of plasma membrane enriched in cholesterol and sphingolipids. Longer and more saturated acyl chains. Thicker, less fluid environment, higher melting temp. Selectively include or exclude proteins. Important for signaling events. Structure regulated by cholesterol; if depleted in cholesterol raft dissociates.