L20 Membranes & Lipids

Question 1

which membranes do gram -ve bacteria have?

Answer 1

inner membrane
peptidoglycan layer
outer membrane

Question 2

which membranes do gram +ve bacteria have?

Answer 2

thick peptidoglycan layer
inner membrane

no outer membrane

Question 3

what is the function of membranes?

Answer 3

Provide a functional barrier – compartmentalization of cells.

Provide cells with energy (from chemical and charge gradients).

Organize and regulate enzyme activities.

Facilitate signal transduction.

Supply substrates for biosynthesis and for signaling molecules.

Protein recruitment platform.

Question 4

what determines the number of proteins and lipids in a membrane?

Answer 4

function

Question 5

which lipids do membranes contain?

Answer 5

glycerophospholipids (phospholipids)

sphingolipids

sterols

Question 6

what allows membranes to become a bilayer?

Answer 6

the fact that most lipids and amphipathic and also their shape

Question 7

are fatty acids aliphatic or amphipathic and what is their terminal end?

Answer 7

alipathic with a terminal carboxylic end

Question 8

how do hydrophilic molecules dissolve in water?

Answer 8

they contain charged or uncharged groups which form electrostatic interactions or hydrogen bonds with water molecules

Question 9

why are hydrophobic molecules insoluble in water?

Answer 9

most atoms are uncharged and nonpolar so they cannot form energetically favourable interactions with water

Question 10

how do fatty acids vary?

Answer 10

in chain lengths, double bond number, double bond position and hydroxylation

Question 11

what is the nomenclature for fatty acids?

Answer 11

XX:Y n-y

XX = number of carbons in the chain

Y = level of chain saturation (number of double bonds)

n-y = position of first double bonded carbon counting from the methyl terminus

Question 12

what are the differences between saturated and unsaturated lipid tails and what is the importance in these differences?

Answer 12

Saturated lipid tails: Fatty acids in lipid tails that do not have double bonds between adjacent carbon atoms. This lipids tail are relatively straight.

Unsaturated lipid tails: Fatty acids in lipid tails that contain one or more double bonds between adjacent carbon atoms. Unsaturated lipid tails can have a cis double bond - makes a 30o kink or a trans double bond that does not affect their structure.

Differences in the length and saturation of thefatty acid tails are important. They influence how phospholipids pack against one another (membrane rigidity).

Question 13

how can the linkage of the sn-1 position and the head group differ in fatty acids?

Answer 13

The sn‐1 fatty acid is usually saturated (without double bonds) or monounsaturated.

The sn‐2 fatty acid is more often monounsaturated or polyunsaturated (multiple double bonds).

Question 14

which phospholipids have a net negative charge?

Answer 14

amnionic phospholipids - PS, PI, PG, CL

Question 15

which phospholipids have zero charge?

Answer 15

zwitterionic

Question 16

which phospholipids contain reactive amines that can participate in hydrogen bonds?

Answer 16

PS and PE

Question 17

which phospholipids are bulky and so packaging is affected?

Answer 17

PI, PC and CL

Question 18

which organelle specific lipids are only found in mitochondria?

Answer 18

PG and cardiolipins

Question 19

how are phosphoinositides lipids (PIPs) generated?

Answer 19

by head group phosphorylation at positions 3, 4 and 5 of phosphatidylinositol

Question 20

how many species of PIP are there and which one is the most abundant in the mammalian plasma membrane?

Answer 20

they are 7 species of PIP which have a saturated and a polyunsaturated lipid tail

PI(4,5)P2) is the most abundant in the mammalian plasma membrane

Question 21

what can change the shape of lipids?

Answer 21

phosphorylation and dephosphorylation which occurs via kinases and phosphatases

Question 22

what does PTEN protein dephosphorylate, and into what?

Answer 22

it dephosphorylates PI(3,4,5)P3 into PI(4,5)P2

Question 23

what are glycerophospholipids made up of?

Answer 23

sphingoid base, N-acyl chain and a head group

Question 24

what is the most common sphingolipid and what headgroup does it have?

Answer 24

sphingomyelin (SM), has a PC headgroup

Question 25

how are interactions of sphingolipids with cholesterol or polar parts of proteins able to occur?

Answer 25

due to amide group forming H bonds

Question 26

why do N-acyl chains of sphingolipids tend to be more saturated?

Answer 26

so they are able to pack more closely

sphingolipids can be longer than the acyl chains of glycerophospholipids

Question 27

what % of the outer leaflet do glycosphingolipids make up?

Answer 27

5%

Question 28

what do glycosphingolipids (glycolipids) do in the membrane?

Answer 28

Important role in interactions of the cell with its surroundings (cell-cell adhesion).

Allow membranes to act as recognition sites for certain chemicals.

Question 29

how/why do glycosphingolipids self-associate?

give an example

Answer 29

The glycolipids tend to self-associate via hydrogen bonds between their sugars and through their lipids tails.

Self-aggregation of GM1 lipids may be driven by the sugars in GM1 lipids. Patches of glycosphingolipids were seen in simulations.

Question 30

what is the general structure of sterols and what does it’s shape allow?

Answer 30

Sterols have a hydroxyl group and a hydrocarbon tail.

Its size and shape allows cholesterol to interact with pockets in membrane proteins.

Question 31

what is the most common sterol in:

• animals
• yeast and fungi membrane
• plants (2)

Answer 31

animal = cholesterol
yeast/fungi = ergosterol
plant = sitosterol and stigmasterol

Question 32

how does the presence of sterols affect the membrane?

Answer 32

Its presence increases thickness, packing, and compressibility of membranes while it decreases mobility of lipids and proteins.