BIOL2210 Membranes and lipids

how does lipid content influence the membrane

it influences its physiological properties (their normal functions)

what are the 3 primary functions of membranes

keep toxic substances out

allow selective passage of mols

separate metabolic processes

what is the benefit of separating metabolic processes

concentrate and isolate enzymes and reactants to increase reaction rate and efficiency

general role of lipids and proteins in a membrane

provide flexibility and maintain chemical environment via transport of mols

define lipid

any hydrophobic mol insoluble in water but soluble in organic solvents (chloroform)

3 types of membreane proteins

peripheral

integral

lipid linked

how are peripheral membrane proteins connected to the membane

via interactions with other proteins in memb

how are integral proteins connected with the membrane

inserted into and through the bilayer, portions exposed on either side, pass thru once or more

how are lipid linked membrane proteins attached to the membrane

via a lipid linker

(a functional group that attaches protein to lipid tail)

roles of membrane proteins

structural

receptors

transport

signalling

what is the perinuclear space

space between inner and outer bilayers of nucleus

structure of ER

interconnected network of flattened membrane enclosed sacs

structure of Golgi

stack of flattened stacks (cisternae)

structure of transport vesicles

can be vesicular or tubular

what organelle produces the bulk of phospholipids and cholesterol

the ER

what are the two types of lipids

phospholipids and glycolipids

what are the two types of phospholipids

glycerophospholipids and sphingolipids

structure of glycerophospholipid

glycerol with 2 FA chains via ester bond as tail

phosphate group as head

charge of the phosphate head

negative (hydrophilic)

charge of aliphatic carbon tails of phospholipids

uncharged (hydrophobic)

other word for fatty acid chains

fatty acyl chains

what are fatty acids

long aliphatic carbon chain with terminal carboxylic acid

are there usually an even or odd number of CH2 groups in fatty acids

even

how are phospholipid fatty acid chains ususally asymmetrical

different length

presence/absence of C=C bond

what angle of projection does a single C=C bond in a FA chain produce

30 degrees

do unsaturated fatty acids contain cis or trans C=C bonds

cis

how does packing and fluidity of a membrane differ with unsaturated phospholipids

decreased closed packing

increased fluidity

are saturated or unsaturated fatty acids liquid at room temperature

unstaturated

what does it mean if membrane topology is maintained upon vesicle fusion with a membrane

orientation is maintained

cyto facing side stays cyto facing

how do different classes of glycerophospholipids differ

by the mol bound to phosphate

what are groups commonly bound to the phosphate of glycerophospholipids

glycerol

choline

serine

ethanolamine

phosphatidylcholine

choline bound to pi

most abundant PL in membranes

phsophatidylethanolamine

ethanolamine bound

second most abundant

small head group allows for easier positioning of proteins within membrane

phosphatidylserine

typically confined to cyto facing face

presence on outer face of dying cells signals for phagocytosis by macrophage

phosphatidylinositol

inositol sugar bound

less common than others

can be pi to prod phosphatidylinositol phosphate , diphosphate or triphosphate (PIP, PIP2, PIP3)

are important signalling mols

examples of gycerophospholipids

PC

PS

PE

Phosphatidylinositol

what is a sphingolipids

type of phospholipid with an amide bond between a FA and sphingosine

what is a ceramide

sphingosine with FA bound by amide bond

roles of sphingolipids

structural

signalling

sphingomyelin structure

ceramide with phosphocholine or phosphoethanolamine bound

where is sphingomyelin found and whats its role

in myelin sheath of neurons (most in exoplasmic leaflet)

electrically insulates cell axon

cause of multiple sclerosis

activation of sphingomyelinase-2 breaking down sphingomyelin into a ceramide

do plants bacteria and mammals all have cholesterol

no, only mammals

role of cholesterol

maintain membrane integrity and fluidity

structure of cholesterol

small hydroxyl head with large aliphatic tail

how does cholesterol stabilise the membrane

polar hydroxyl head group interact with phosphate head of PL and hold membrane together

prev membrane breakdown at high temps

how does cholesterol maintain membrane fluidity

prevents PL from packing too close as at low temperatures they would become rigid

source of cholesterol

mostly made but some through diet

what is cholesterol and important precursor for

many signalling molecules

how are PLs and cholesterol transported around the body

in lipid particles

structure of glycolipids

sugar on lipid projected into aqueous environment

roles of glycolipids

stability and recognition

allow cell attachement hence tissue formation

are sphingomyelin or PL bilayers thicker

sphingomyelin

how does cholesterol affect the thickness of the bilayer

increases PL bilayer thickness

less so for sphingolipid bilayer

how does cholesterol increase the thickness of phospholipid bilayers

through lipid ordering

why does cholesterol increase the thickness of sphingolipid membranes less

are already more ordered than PL membs

shape of phosphatidylcholine

cylinder shape

form flat monolayers

shape of phosphatidylethanolamine

conical shape

as smaller head group

how is membrane curvature produced

different endoplasmic and exoplasmic distributions of PE and PC

what are lipid rafts

clusters of cholesterol and sphingolipids with proteins that form microdomains

how can lipids move within a bilayer

rotate

lateral diffusion

flip

does membrane flipping occur spontaneously

yes, but often catalysed by flippases

do all flippases require ATP

Not all, only unidirectional ones

what cells are specialised for triglyceride formation and breakdown

adipocytes

what catalyses triglyceride breakdown

hormone sensitive lipases

can utilisation lipids for energy be both aerobic and anaerobic like carbohydrates

No, only aerobic

(req oxidation of FA)

structure of lipid droplets

lipid ester core surrounded by phospholipid monolayer

are organelles

store lipids

when are lipid droplets formed

when lipid levels exceed those needed for membranes

role of diacylglycerol and posphatidylinositol phosphates

involved in intracellular signalling (Calcium med

what are prostaglandins involved in

inflammation and immunity