Lipids and membrane structure Flashcards
Features of phospholipids
-Major component of all membranes
-Spontaneously form bilayer in aqueous environments
-Polar head group attached to backbone (glycerol) by phosphate group
-2 fatty acyl side chains lined to glycerol backbone via ester bonds
-Amphipathic - polar head group and non-polar FA tail
What is the fluid mosiac model of membrane structure?
-Islands of protein in a sea of lipid
-Hydrophilic heads -Hydrophobic tails
-4-5nm width
How does the composition of cell membranes vary?
-Only plasma membrane has glycosylated proteins
-Lipid bilayers are asymmetrical
What is membrane fluidity and why is it important?
-the ease with which lipid molecules move about in the plane of the bilayer
-important in the regulation of membrane function (movement of proteins, signalling, exocytosis)
What are the 4 layers of cell membrane and major component of each one?
-Plasma membrane
=>cholesterol
-Outer mitochondrial membrane
-Inner mitochondrial membrane
-Nuclear membrane
=>phosphatidylcholine
What regulates membrane fluidity?
-Increase in short chain fatty acids reduces van der waals interactions between fatty acids which increases fluidity
-Kinks in unsaturated fatty acids reduce van der waals interactions with other lipids and increases fluidity
-High cholesterol content restricts random movement of polar heads, orders the lipid bilayer and decreases fluidity
What are lipid rafts?
-Specialised membrane microdomain
-More ordered, less fluid
-Increased level of cholesterol
-Increased level of sphingomyelin and gangliosides
-Allows close interaction between receptors and signalling molecules
What are the types of membrane proteins and what do they do?
-Structural - cell to cell contact, attachment of cytoskeleton
-Receptors - signal recognition and transmission
-Ion channels - maintenance of ionic gradients
-Transporters - import and export of substrates
-Enzymes - catalysis
What are integral (intrinsic) proteins?
-Embedded in lipid bilayer
-Most span entire bilayer
-Transmembrane spanning domains are alpha helices or beta sheets
What are anchored proteins?
-Not deeply embedded in the bilayer
-Anchored to membrane by covalent bonds with fatty acids or glycolipids on the surface
What are peripheral (extrinsic) proteins?
-Attach to membrane surface by ionic interactions with integral proteins or with polar head group of phospholipids
What proteins are removed by high salt, urea?
-Peripheral proteins
What proteins are removed by detergent?
-Peripheral
-Anchored
-Integral
What proteins are removed by phospholipases?
-Peripheral
-Anchored
What are phospholipases?
-Important class of enzymes
-Bind to membrane and selectively hydrolyse components of phospholipids
-E.g. Phospholipases A2 (PLA2s) release fatty acids from the second carbon group of glycerol
Definition of lipid
-Something that is insoluble in water but soluble in fat and organic solvents
Function of lipids
-energy store
-precursors for vitamins and steroid hormones
What are triacyclglycerols?
-Ester of 3 fatty acids and glycerol
-Stored in adipose tissue
Saturated vs unsaturated fatty acids
-Saturated = no double bonds between carbon
-Unsaturated = At least 1 double bond between carbon
What are polyunsaturated fatty acids?
-More than 1 double bond between carbon
What are phospholipids?
-Glycerol, 2 fatty acids (hydrophobic), phosphate head group (hydrophilic)
What are glycolipids?
-Glycerol
-2 fatty acids
-Head group containing sugars
What is sphingosine?
-Some lipids replace glycerol with sphingosine
-Sphingosine and a single fatty acid chain form a unit called ceramide
Importance of ceramide in neuronal plasma membranes
-Ceramide is found in some glycolipids (e.g. GM1 ganglioside)
-Gangliosides make up 10-20% of neuronal membranes and are involved in the formation of synapses
Structure of steroids
-Common structure
-Multi-ring hydrophobic region
-Hydrophilic region
Significance of cholesterol
-Steroid that forms part of membranes
-Is the precursor of steroid hormones
