biological membranes

Question 1

what are FA composed of?

Answer 1

long chains of hydrocarbon carboxylic acids
-up to 24C long
-general formula CH3(CH2)nCOO-

Question 2

what conformation are most naturally occuring double bonds in?

Answer 2

cis

Question 3

what does each number of the short hand notation for naming FA represent?

Answer 3

the first number is the number of carbons, the second number is the number of double bonds
-the number beside the delta sign indicates what carbon the double bond is at

Question 4

what affect does increasing the number of carbons have on the MP of FA?

Answer 4

increasing chain length will increase MP

Question 5

what affect does increasing the number of double bonds have on the MP of FA?

Answer 5

increasing the number of double bonds will decrease the MP

Question 6

what 2 factors affect FA MP?

Answer 6

length and unsaturation

Question 7

does unsaturation or chain length have a greater effect on FA MP?

Answer 7

unsaturation

Question 8

what is the packing structure of saturated vs unsaturated FA?

Answer 8

saturated FA pack closely together while unsaturated FA cannot pack closely due to a bend in their chain

Question 9

How are fatty acids stored?

Answer 9

Triacylglycerol (TAG) is a way of storing FA
-very hydrophobic (not amphipathic)
-three acyl chains attached to glycerol

Question 10

what is the most common form of triacylglycerols (TAG)?

Answer 10

mixed TAGs
-triacylglycerol with more than one different FA

Question 11

How does melting point differ depending on saturation and chain size?

Answer 11

MP is lower for TAGs containing unsaturated FA or shorter chains

Question 12

what lipids make up membranes?

Answer 12

glycerolphospholipids, sphingolipids and cholesterol

Question 13

are glycerophospholipids amphipathic, polar or hydrophobic?

Answer 13

amphipathic

Question 14

what makes glycerophospholipids similar to triacylglycerol?

Answer 14

it has a fatty acyl group covalently attached

Question 15

what are chemical properties of cholesterol?

Answer 15

mostly hydrophobic
-rigid, non-polar and weakly amphipathic (1 OH group)

Question 16

can cholesterol form a membrane on it’s own? what is its function?

Answer 16

no it cannot form membranes alone, the OH associates with polar headgroups of other lipids and non-polar portion found inside membrane

-cholesterol is needed in order to maintain membrane fluidity and rigidity

Question 17

what occurs to amphipathic molecules in water? what do lipids form? what do FA form?

Answer 17

they form micelles or bilayers
-lipids form a bilayer
-FA form micelles

Question 18

why do amphipathic molecules form bilayers or micelles in water?

Answer 18

this arrangement eliminates unfavourable contact between water and hydrophobic tails while permitting solvation of polar head groups

Question 19

what can lipid bilayers form?

Answer 19

spherical vesicles (liposomes)

Question 20

what is the composition of lipid bilayers?

Answer 20

changes depending on lipid composition but it non-covalently assmebles and contains:
-acyl chain
-polar head group

Question 21

what factors contribute to a thicker lipid membrane?

Answer 21

more carbons/larger heads = thicker membrane

Question 22

what is transition temperature?

Answer 22

the temperature at which a lipid bilayer transitions from an ordered crystaline to a more fluid state

Question 23

what does transition T depend on?

Answer 23

acyl chain unsaturation and length

Question 24

what occurs to lipid bilayers when they are below transition T?

Answer 24

acyl chains pack together in a gel-like solid state

Question 25

what occurs to lipid bilayers when they are above transition T?

Answer 25

acyl chains move freely and rapidly

Question 26

how does transition T differ between artificial and biological membranes?

Answer 26

sharp for artificial membranes and not sharp for biological membranes (mixture of compounds)

Question 27

When T decreases, what structures are embedded into the membrane?

Answer 27

more unsaturated and shorter FA

Question 28

When T increases, what structures are embedded into the membrane?

Answer 28

more saturated and longer FA

Question 29

why does cholesterol work to increases membrane rigidity?

Answer 29

because it is rigid and planar it is able to limit rotational movement of neighboring acyl tails---> increasing van der waal interactions

Question 30

when T is low, what is the affect of cholesterol?

Answer 30

prevention of close packing between acyl chains

Question 31

when T is high, what is the affect of cholesterol?

Answer 31

decreases motion/disorder of acyl chains---> increasing rigidity

Question 32

in what way are lipids able to move within a bilayer?

Answer 32

they move freely and rapidly by lateral diffusion

Question 33

are lipids able to undergo transverse diffusion?

Answer 33

a significant energy barrier prevents transverse diffusion at appreciable rates -flipases increase rate of transverse diffusion

Question 34

what kinds of membrane proteins are there?

Answer 34

integral, peripheral and lipid-linked

Question 35

what kinds of AA side chains would you expect to see on the portion of an integral membrane protein that interacts with the acyl tails?

Answer 35

hydrophobic side chains

Question 36

are regular structures able to cross membranes?

Answer 36

yes, alpha-helices and beta-sheets are both able to cross membranes

Question 37

what kind of transport do proteins adhere to within the membranes?

Answer 37

lateral movement -cannot easily undergo transverse movement

Question 38

what kinds of molecules are able to cross the lipid bilayer by simple diffusion?

Answer 38

small, non-polar molecules

Question 39

what does the rate of simple, unmedieated diffusion depend on?

Answer 39

-size of molecule (smaller move faster) -[gradient]; larger gradient increases diffusion -lipid solubility (greater solubility increases diffusion rate)

Question 40

how do transport proteins aid in transport?

Answer 40

by reducing activation energy barrier needed for transport

Question 41

what type of transport do porins and ion channels enable?

Answer 41

passive transport via membrane-spanning pores

Question 42

are ion channels selective or non-selective?

Answer 42

they are highly selective

Question 43

are porins selective or non-selective?

Answer 43

they are non-selective

Question 44

what is the structure of a porin?

Answer 44

trimers with water-filled pore in the center

Question 45

how does a transporter protein differ from a transport protein?

Answer 45

transporter proteins are carrier proteins and they do not have membrane-spanning pores -they have conformational changes -selective of substrate -can be passive or active

Question 46

what kind of kinetic curve would you expect to see for passive transport by carrier proteins?

Answer 46

hyperbolic

Question 47

summarize the 4 ways a substrate can be transported across a membrane

Answer 47

1) simple diffusion 2) passive, channel mediated transport 3) passive, carrier mediated transport (transporter) 4) active, carrier mediated transport (transporter)

Question 48

what are the 3 classifications of transporter proteins in terms of how they transport?

Answer 48

uniport - one molecule one direction symport - 2 of the same molecules in the same direction antiport- 2 different molecules in different directions

Question 49

what is the difference between primary and secondary active transport?

Answer 49

primary uses a direct source of ATP while secondary uses an ion gradient created from primary transport

Question 50

what are the steps required for the Na+/K+ ATPase?

Answer 50

1) 3 Na+ molecules bind 2) ATP binds and a phosphoryl group is transferred to the side chain of the pump and ADP is released 3) A conformational change occurs expelling Na+ to extracellular space 4) 2 K+ molecules bond and the side group containing P is hydrolyzed to release inorganic phosphate 5) this causes a conformatinoal change and K+ is released into the cell

Question 51

where is the [glucose] higher in the Na+ glucose transporter system? what is the delta G for this transport?

Answer 51

[glucose] inside the cell > [glucose] outside the cell delta G > 0 for the transport of glucose inside the cell -going against [gradient]

Question 52

where is the [Na+] higher in the Na+ glucose transporter system? what is the delta G for this transport?

Answer 52

[Na+] inside the cell < [Na+] outside the cell delta G is < 0 for the transport of Na+ into the cells -going with [gradient]

Question 53

how is glucose able to enter the cell if the delta G for the Na+/glucose transport system is > 0?

Answer 53

The transport of Na+ provides energy for glucose import into the cell