week 2 reading

Question 1

phosphatidylserine: unique characteristic

Answer 1

negatively-charged

Question 2

lipid bilayer: how is it held together?

Answer 2

noncovalent interactions

Question 3

sphingomyelin composition

Answer 3

fatty acid-NH2
phosphocholine-OH

Question 4

sphingosone composition

Answer 4

amino + 2 -OH groups

Question 5

cholesterol orientation

Answer 5

-OH groups close to polar heads of adjacent phospholipids

Question 6

sterol composition

Answer 6

steroids with polar -OH, nonpolar hydrocarbon chains

Question 7

spontaneous bilayer formation

Answer 7

shape and amphiphilic nature allows phospholipids to spontaneously form bilayers in aqueous environments

Question 8

self-sealing properties

Answer 8

small tear exposes free edge to water
energetically unfavorable

Question 9

flip-flop process

Answer 9

monolayer migration, very slow bc hydrophilic heads must enter and pass through hydrophobic core
(very rare)

Question 10

flip-flop process exception

Answer 10

cholesterol

Question 11

rapid location change within monolayer

Answer 11

rapid lateral diffusion: takes one second to diffuse length of cell
individual lipid molecules rotate about long axis, have flexible hydrocarbons

Question 12

rapid location change within monolayer: problem

Answer 12

synthetic bilayers’ individual phospholipids are confined to their own membranes
- asymmetric expansion b/c molecules are only made in cytosolic layer of ER, can’t migrate to non-cytosolic membrane

Question 13

fluidity: hydrocarbon chain length

Answer 13

lower temperature needed for shorter hydrocarbon chains, unsaturated chains

Question 14

fluidity: shorter chains

Answer 14

shorter chains have less interaction between hydrocarbon tails in both same and opposite monolayer

Question 15

fluidity favored by:

Answer 15

cis bonds
- kinks, tight packing

Question 16

sterols: modulate bilayer properties

Answer 16

enhance permeability-barrier properties
- cholesterol interacts so -OH is by polar heads of phospholipids by polar heads to stiffen hydrocarbon chains closest to polar heads
- decreases permeability in small water-soluble molecules
- doesn’t affect fluidity

Question 17

TM proteins

Answer 17

cross bilayer in alpha helix
- single or multipass
- peptide bonds driven to form hydrogen bonds bc bonds are polar and H2O is absent in bilayer

Question 18

beta barrels

Answer 18

form channels
all hydrogen bonds must be satisfied
outside = hydrophobic
sheet exposing edge is unfavorable

Question 19

glycosylation

Answer 19

oligosaccharides on non-cytosolic side
cytosol is a reducing environment

Question 20

membrane asymmetry: functional importance

Answer 20

• converting extracellular signals to intracellular
• cytosolic proteins binding to specific head groups in cytosolic monolayer
• phospholipases activated by extracellular signals cleave certain phospholipid molecules: generated fragments act as short-lived intracellular messengers

Question 21

lipid kinase function in asymmetry

Answer 21

can add phosphate groups to inositol rings to create binding sites
- recruit cytosolic proteins to membrane

Question 22

phospholipase c function

Answer 22

intracellular messenger
- cleaves inositol phospholipid into two fragments
- one stays in membrane to activate PKC, one enters cytosol to stimulate Ca2+ release from ER

Question 23

glycolipids

Answer 23

always on non-cytosolic leaflet
- protection from harsh conditions
- electric fields affect ion concentrations
- cell-recognition processes

Question 24

membrane transport: principles

Answer 24

protein-free lipid bilayers are impermeable to ions
rate of diffusion varies based on hydrophobicity
- more nonpolar = more rapid diffusion
- smaller = faster diffusion

Question 25

passive transport

Answer 25

downhill via concentration gradient

Question 26

active transport

Answer 26

uphill via ion gradient or ATP hydrolysis

Question 27

coupled transporters

Answer 27

use energy from concentration gradient to couple uphill transport of 1 solute to downhill transport of another

Question 28

p-type pump

Answer 28

self-phosphorylate during pumping cycle
ATP –> ADP + Pi — Pi binds to pump
includes ion pumps

Question 29

ABC transporters

Answer 29

need ATP
ATP binds to each side and separates to make channel
small, organic molecule transport

Question 30

V-type

Answer 30

transports H+ into organelles
ATP synthase, ATP hydrolysis