Lipids and Membranes

Question 1

what are functions of lipids?

Answer 1

a)membrane components (phospholipids, sphingolipids, glycolipids, sterols)
b)energy storage: triglycerides
c)digestion: bile acids
d)biological signals: prostaglandins, hormones, 2nd messengers
e)other: pigments, waxes, vitamins, scents

soluble in non-polar solvents

Question 2

fatty acids

Answer 2

-components of membranes and triglycerides
-polar and nonpolar components (amphipathic)

Question 3

triaclycerols (triglycerides)

Answer 3

storage form of fatty acids
-provides energy reserves
-fatty acid esters of glycerol

Question 4

saponification

Answer 4

hydrolysis of fatty acids onto glycerol

Question 5

phospholipids

Answer 5

-contains one phosphate group (with -X) and 2 fatty acids

Question 6

sphingolipids

Answer 6

-membrane lipids
-contains sphingosine, fatty acid, and phosphate group (with -X)
-resemble phospholipids

Question 7

waxes

Answer 7

esters of long chain fatty alcohols
-lanolin, carnauba wax, spermaceti oil, coatings of fruits
-hydrophobic barrier

Question 8

sterols

Answer 8

components of eukaryotic membranes
-contains an hydroxyl group

Question 9

steroid hormones

Answer 9

contains a ketone

Question 10

bile acids

Answer 10

digestive “detergents”
-breaks down fat

Question 11

prostaglandin

Answer 11

-inflammation
-blood vessel contraction
-pain/fever
-uterine contraction
-sleep/wake cycle

Question 12

“fat soluble” vitamins

Answer 12

vitamin A,D,E,K are lipids

Question 13

terpenes

Answer 13

isoprene derivative ->scents

Question 14

functions of biological membranes

Answer 14

-selective permeability barrier
-organize complex reactions
-intracellular compartmentalization
-sensory transduction/amplification

Question 15

how do membrane lipids assemble?

Answer 15

-they self assemble
-fatty acids are wedge-shaped->form micelles
-membrane lipids are cylindrical->form vesicles (lipid bilayer)
-spontaneous assemble (favorable deltaG)
->hydrophobic interactions, Vanderwaals, h-bonds
->increase entropy of water

Question 16

what are important properties of membranes?

Answer 16

1)self-sealing
2)highly impermeable to polar or charged molecules (except for water)

Question 17

integral proteins

Answer 17

-embedded in lipid bilayer
-firmly held in membrane by hydrophobic interactions
-removable only by detergent

Question 18

peripheral proteins

Answer 18

-loosely bound to external position of membrane
-removable by high salt, urea, etc.
-easily removed

Question 19

lipid “anchored” proteins

Answer 19

-peripheral but covalently bound to a membrane lipid

Question 20

polytopic

Answer 20

protein goes through both leaflets of membrane

Question 21

monotopic

Answer 21

protein goes through one leaflet of membrane

Question 22

detergents

Answer 22

solubilize and disrupt membranes
-hydrophobic domains become coated with detergents
-pulls off integral and peripheral membranes

Question 23

fluid mosaic model of membranes

Answer 23

Singer Nicholson
- integral proteins->”icebegs” floating in 2D lipid “sea”
-fluid structure
Evidence:
1)lipids diffuse rapidly in plane of membrane (laterally) (within 1 leaflet)
2)integral membrane proteins diffuse rapidly

Question 24

membrane asymmetry

Answer 24

-proteins have unique orientation
-composition of lipids differs btwn 2 “leaves” of bilayer

Question 25

maintenance of asymmetry

Answer 25

-transverse diffusion of lipids is very slow -transmembrane proteins don't "flip"

Question 26

flippase

Answer 26

transport of lipids towards the cytoplasm and requires ATP -against concentration gradient

Question 27

floppase

Answer 27

transport of lipids away from the cytoplasm and requires ATP -against concentration gradient

Question 28

scramblase

Answer 28

bi-directional, non-energy dependent transport of lipids -movement down concentration gradient

Question 29

membrane rafts

Answer 29

-enriched in sphingolipids and cholesterol -everything on raft stays, but raft can move as one unit through the membrane

Question 30

how is membrane fluidity affected by temperature?

Answer 30

low temp->paracrystalline, more solid, thicker, risks breaking high temp->leaky and porous, thinner

Question 31

other factors affecting membrane fluidity?

Answer 31

1) degree of saturation -increase of saturation->decrease fluidity 2) length of fatty acid tail -increase length->decrease fluidity 3)sterol content

Question 32

how do sterols plasticize the membrane?

Answer 32

high temp-> sterols decrease fluidity -rigid sterol molecule restricts movement of lipid tails -decreases fluidity low temp-> sterols increase fluidity -sterols prevents "crystalization" of membrane by blocking interactions btwn tails

Question 33

diffusion

Answer 33

movement from higher to lower concentration (no energy required)

Question 34

simple diffusion

Answer 34

movement of molecules from high to low through semipermeable membrane

Question 35

facilitated diffusion

Answer 35

"passive" transport protein-mediated using channels and carrier proteins

Question 36

active transport

Answer 36

transport against concentration gradient (requires energy) -protein "pumps" mediate

Question 37

channels

Answer 37

-hydrophilic pores -high capacity -nonsaturable -lower free energy barrier for movement of polar molecules across

Question 38

carriers

Answer 38

-permeases/transporters -undergo conformational change -saturable -slower than channel proteins

Question 39

glucose permease

Answer 39

-a carrier -specific to D-glucose -reversible passive transport

Question 40

ligand gated channels

Answer 40

depolarization: Na+ and charge binds to channel, channel opens

Question 41

voltage-gated channels

Answer 41

self-propagating depolarization in muscles and nerve terminal -static triggers the opening of channels

Question 42

primary active transport

Answer 42

-transporters pump molecules against concentration gradient -pumping coupled directly to use of energy source -Na+/K+ ATPase pump -ATP hydrolysis induces change in confirmation

Question 43

Na+/K+ ATPase

Answer 43

-creates ion gradient -creates charge gradient -provides energy for secondary transport systems 2K+ in, 3N+ out

Question 44

secondary active transport

Answer 44

-energy stored in ion gradients drives transport of other molecules -symporter (move in same direction) -antiporter (move molecules in opposite directions)