Week 4 - lipids and cell membranes part 1 Flashcards
Name some common features of biological membranes
- sheet like, to molecules thick, between 60-100 A thick
- mainly comprise lipids and proteins
- membrane lipids are small amphipathic molecules
- specific proteins mediate distinctive functions
- membrane are non-covalent
- asymmetric - two faces always differ
- fluid structures - lipids diffuse rapidly in the plane
- polarised, inside cell typically -60mV
Name 6 membrane functions
- selective barrier
- transport and excretion
- defence
- energy storage/ accumulation
- assimilation/ synthesis
- information
Describe the nature of membrane lipids
- amphipathic molecules containing hydrophilic an hydrophobic moiety
name the three functional groups of a fatty acid
- hydrogen
- alkyl
- carboxyl
what are fatty acids?
long chain hydrocarbons
How many saturated carbons does octadecanoic have?
18:0
How many saturated carbons does octadecenoic have?
18:1
How many saturated carbons does octadecadienoic have?
18:2
How many saturated carbons does octadecatrienoic have?
18:3
What does palmitate consist of?
16 carbon saturated fatty acids
What does oleate consist of?
18-carbon with a single cis double bond
Atom numeration
- double bond nomenclature:
1. triangle and nr of C from C1
2. or omega and nr of C form CH3
eg. cis-delta^9-octadecenoate or omega-9
What do you know about the chain length and saturation in common fatty acids?
- usually contain an even number of carbon atoms (14-24)
- 16- and 18- are common
Why is there a dominance of even numbered carbon atoms?
according eight eh way fatty acids are biosynthesised
How does an increasing number of double bonds affect fluidity?
- increases fluidity
How does an increasing number of carbons affect fluidity?
decreases fluidity
name three common types of membrane lipids
- phospholipids
- glycolipids
- cholesterol
What does a phospholipid consist of?
- constructed from four components:
1. one or more fatty acids
2. platform to which they are attached (alcohol eg. glycerol or sphingosine)
3. phosphate
4. alcohol attached to phosphate
Describe the chemical structure of the simplest phospholipid
- acyl groups with fatty acid hydrocarbon chains
- phosphatidate (diacylglycerol 3-phosphate)
- a phosphate
- an alcohol attached to phosphate
What is phosphatidate?
- simplest phoshoglyceride consists of glycerol platform esterified to the carboxyl groups of the two fatty acid chains C-1 and C-2, C-3 is esterified to phosphoric acid
how are the main phospholipids created?
- derived from phosphatidate
- by formation fo ester bond between phosphate group of phosphatidate and hydroxyl group of one of several alcohols
What are the most common alcohols?
- serine
- ethanolamine
- choline
- glycerol
- inositol
What does PS stand for?
phospatidylserine
What does PC stand for ?
phosphatidylcholine
What does PE stand for?
Phosphatidylthanolamine
What does PI stand for?
Phosphatidylinositol
What does DPG stand for?
Diphosphatidylglycerol (cardioplipin)
is sphingomyelin derived form glycerol?
no
Where is sphingomyelin derived from?
sphingosine, an amino alcohol with long saturated hydrocarbon chain - sphingosine backbone linked to fatty acid by amide bond
- primary alcohol esterified to phosphorylcholine
What are glycolipids?
sugar containing lipids derived form sphingosine
- aino gourp is acylated by fatty acid
- primary alcohol esterified to one or more sugars
- glycolipids asymmetric - sugar always on the extracellular side of membrane
What else do more complex glycolipids eg. gangliosides contain?
a branched chain of as many as seven sugars
What is cholesterol?
a lipid based on a steroid nucleus
- in membrane oriented parallel to fatty acid chains of the phospholipids, hydroxyl group interacts with the nearby head groups
- absent in prokaryotes
- distribution varies in mammals high in nerve cells, Low in some intracellular membranes
What are Racheal membranes built form?
ether lipids and branched chains
How do the membranes of archaea differ from those of eukaryotes?
- non-polar chains are attached by ether rather than ester bonds
- alkyl chains are branched
what might the ability of archaean lipids to resist hydrolysis and oxidation help organisms to survive?
in extreme conditions such as high T, low pH and high salt, under which some of these archaea grow
What do phospholipids and glyocolipids readily form?
sheets in aqueous media
What are the favoured structures for most phospholipids and glycolipids in aqueous media?
bimolecular sheet rather than micelle (bulkiness of fatty acids)
How do lipid players form?
spontaneously by a self-assembly process to minimise the exposure to water of the hydrophobic tails
What can be formed from phospholipids?
lipid vesicles, liposomes
What are lipid vesicles or liposomes?
aqueous compartments enclosed by a. lipid bilayer used to study memebrane permeability or to deliver chemicals to cells
what will happen after glycine and H20 are filled into a beaker with phospholipid layer on the bottom ?
sanitation -> lipids will form into circles, form a bilayer
gel filtration -> glycine trapped in lipid vesicles
What are liposomes?
- outer aqueous compartment, inner aqueous compartment separated by a bilayer membrane
How can larger vesicles than 500 A be prepared?
by slowly evaporating the organic solvent form a suspension of phospholipid in a mixed solvent system
Explain experiments to develop clinical uses of liposomes
- liposomes containing drugs or DNA for gene therapy can be injected into patients
- these liposomes fuse with plasma membrane of many kinds of cells, introducing into the cell the molecules they contain
- drug delivery using such lysosomes can lessen drug toxicity particularly if selective fusion of lipid vesicles with specific cell types become possible
What are lipid bilayers highly impermeable to?
ions and most polar molecules
What is an exception to the permeability of membranes?
because of its small size, high conc and lack of full charges, water can pass the membrane even tho its polar
Why carries out most membrane function?
- proteins
Do membranes differ in their protein content? give examples
yes - myelin, a membrane that insulates nerve fibres has a low protein content - 18 %
Relatively pure lipids such as myelin are what?
good insulators
What does a plasma membrane of most cells that are metabolically active contain?
pumps, channels, receptors, enzymes
What is the typical protein content of some plasma membrane?
50%
Which membranes have the highest protein content? And what % is it?
- energy-transduction membranes
- eg. internal membranes of mitochondria and chloroplasts have highest content of protein
- around 75 %
what technique can be used to show the listing protein composition?
SDS page
What are the types of proteins association with the lipid bilayer?
integral and peripheral
