Lipids And Cell Membranes Flashcards
What are lipids like in water?
Low solubility
Give examples of lipids:
Phospholipids
Fats
Sterols
Vitamins
What do lipids do?
Sources of energy
Form membranes
Participate in cell signalling
What are fatty acids?
Principle store of energy
Rarely free in the body
Structure of fatty acids:
Carboxyl group with long hydrocarbon chain
Naturally occurring = even number of carbons
What are fatty acids usually part of if not free in the body?
Part of lipid molecule
Complexed to carrier protein
Difference between fatty acid chain lengths:
Short + medium chain = absorbed into bloodstream
Long chain = can’t be absorbed
Saturated fatty acids:
No double bonds
Unsaturated (cis) fatty acids:
Double bond
Kink in chain
Unsaturated (trans) fatty acids:
Double bond
No kink in chain
Dangerous to eat
16:0
Saturated
18:1
Unsaturated
20:4
Polyunsaturated
How are double bonds numbered as in fatty acids?
Δ
What are double bonds like in polyunsaturated fatty acids?
Never conjugated
Separated by -CH2
Structure of omega fatty acids:
Unsaturated
Numbered as first c-c bond from methyl end
Give examples of sterols:
Bile acids
Steroid hormones
Vitamins
Cell membranes
What do inherited disorders in lipid pathways result in?
Defects in enzymes which metabolise lipids - lead to lipids accumulation
Which lipids are found in membranes?
Phospholipids
Glycolipids
Sterols
Structure of phospholipids:
Polar head group
Glycerol backbone
Fatty acid chains
What is included in polar head group of phospholipid?
Choline and Phosphate
Structure of glycolipids:
Sphingosine core
What are membrane proteins usually like?
Amphipathic - conflicting properties e.g. both hydrophilic and hydrophobic elements
What results in the lipid bilayer?
Hydrophilic head faces water
Hydrophilic tails shielded from water and lie next to each other
Why are membranes important?
Compartmentalisation
Highly selective barriers
Have sensors (mainly proteins) to respond to internal + external conditions
What’s the fluid mosaic model?
Phospholipid bilayer = fluid matrix and 2D solvent
Lipids + proteins = rotational and lateral movement
What are the two classes of proteins in phospholipid bilayer?
Peripheral proteins (extrinsic)
Integral proteins (intrinsic)
What can alter fluidity in particular parts of cell membrane?
Cholesterol
Where are new phospholipids synthesised?
By enzymes at ER facing the cytosol
They use fatty acids available in cytosol
Where are new phospholipids released in ER?
Into outer leaflet of ER bilayer
Lipids are then transferred to other side by flippases
What are flippases?
Enzymes that can move phospholipids between leaflets
Some are selective for particular phospholipids
What are the different flippase mechanisms?
Pore model = channel moves hydrophilic head to other side
‘Slip-pop’ model = protein jolts
Where does membrane synthesis take place?
In ER
New membrane transported to other parts of cell through series of vesicle budding + fusion
What’s vesicle trafficking?
When bits of membrane pinch off ER to form vesicles and then fuse with other membranes
What’s endocytosis?
Movement of materials into cells via membrane bound vesicles
What’s endocytosis important in?
Immune response
What are lipid rafts?
Organising centre for vesicle trafficking and cell signalling
Why are there membrane proteins?
Molecules require specific transport to diffuse across a lipid membrane
Transmembrane signalling
What do membrane associated proteins usually contain?
Domains that selectively bind to phospholipids - compartment-specific association
What’s PH?
Pleckstrin homology domains
What happens when PH domain is removed?
Alters a protein’s binding properties
Give an example of lipids-linked proteins:
GPI-anchors
What are protein-attached proteins important for?
Signal transduction
What are protein-attached proteins?
They are proteins that don’t bind to the membrane itself but is associated with membrane due to their receptor
