Lipids And Membranes Flashcards
Lipids
Insoluble, mostly non polar and hydrophobic, comprised of fatty acids Functions: Fuels molecules signalling Insulation Solubilise non polar substances
Fatty acid properties
- amphipathic- polar head, non polar tail
- physiological roles- building block for membranes and triaglycerols (TAGs), precursor for prostaglandins (hormones)
- free fatty acids are negatively charged at ph 7.4
- usually esterified (covalently linked to another molecule) and therefore neutralised
- chain length usually even number- 12-24C, 18 and 16 most common, usually not branches in humans
- saturated or unsaturated
C-C single bonds
Free rotation occurs around these bonds
- “trans” confit has lowest energy
- adopt a guache config at increased temp, where they are more fluid
C=C double bonds
Cis config
- no free rotation
Trans does not occur naturally
Decreases melting point
Melting point depends on- length of hydrocarbon chain- increased length increased melting
Degree of in saturation - increased Unsaturation, decreased melting point
Eicosanoids (f.a derivatives)
Synthesised from polyunsaturated fatty acids
Potent physiological properties
Act near site of synthesis and rapidly degrade.
Hydrocarbon chain folds back- ring structure
Prostaglandin
Involved in: Pain Inflammation Birth BP regulation Thrombosis
Used medically
Muscle relaxants
Treatment of stomach ulcers
Triaglycerols (TAGs)
Free fatty acids
Most exist as esters and most are in TAGs
TAG= three fatty acids esterified to glycerol
Glycerol can be esterified to different degrees
Eg. Mono, di, Tri
Natural fats are mixtures of complex and simple TAGs
Mostly 16 and 18C found in nature
Veg oils have more unsat fat, abundance of double bonds and average chain length determine melting point
Function of TAGs
Concentrated energy stores:
Fuel- hydrolysis of C-C release energy. High energy concentration because it does not store with water
Extensive energy stores- sufficient to meet basal energy needs for weeks
Insulation
Buoyancy in marine animals
Properties of TAGs
Melting point - largely due to fatty acid component. Esterification to glycerol has little effect on melting point of the fatty acid. Melting point of TAGs decreases as degree of unsat fatty acids increases
Saponification - fatty acids make micelles trapping non polar grease. Soaps made from fatty acids.
Industrial hardening- industrial hydrogenation process. Converts oil to margarine- Cis to trans
Phospholipids
Glycerol backbone, two fatty acids, one phosphate group and a H or alcohol group
Amphipathic
Not soluble in water but can form extensive bilayers
Double bonds (unsat)- loose lacking in bilayer, soluble inorganic solvent
Cells continuously break down and replace by phospholipase
Sphingolipids- phospholipids with a sphingosine backbone replacing glycerol. Frequently in biological membranes. Very important in nervous tissue.
Myelin is a folded plasma membrane- insulation for nerve cells.
Glycolipids
Amphipathic
- sphingosine backbone
- glycerol as backbone- cell to cell communication
Waxes
Water insoluble esters of long chain fatty acids and long chain alcohol
Soft and pliable when warm, hard when cold.
Water proof later for leaves, feathers etc
Cholesterol
Found in animals Amphipathic but can't form bilayers alone Important component of membranes Modulates membrane fluidity Complex fused ring structure Precursor for bile
Membranes
Define cells and internal structures. Functions: compartmentation, specific transport, energy transduction Endomembrane system Separate from cytoplasm Export and import of molecules
Lipid: protein 50:50
Other components: glycolipids, lipid esters
Estimate the relative composition of plasma membrane, Golgi membrane, endoplasmic reticulum, inner mitochondrial membrane, nuclear membrane.
Mitochondria are like bacterial membrane due to different composition- different density
Thin 5-8nm
Fluid structure
Lipids act as barrier
Impermeable to ions but permeable to H2O
Membrane fluidity
Increase unsaturated fatty acids = increased fluidity
Cholesterol moderates membrane fluidity
Decreased fluidity of the fluid state
Increased fluidity of the gel state
Biological membranes are in a fluid state. Organisms adjust fatty acid composition for life at different temperature to maintain fluidity.
Short or unsaturated fa have lower Mp and stay fluid at lower temperature
Proteins are embedded into lipid bilayer (integral (disrupted with detergents or organic solvents)) or on surface (peripheral (disrupted by high salt or pH))
Movement
Membranes:
Lateral diffusion
Flip flop
Proteins: Lateral Anchored through the membrane Associate in latches Measure freedom with FRAP
Proteins
Associate in rafts- patches which may have different lipids to the rest of the membrane- functional group.
RBC plasma membrane proteins protrude through the membrane into the cytoplasm where they Lin to cytoskeleton proteins.
Proteins stay in place during membrane deformation.
Sources of lipid catabolism
Blood- transport
Adipose tissue- storage
Liver- metabolism
Gut- absorption of fatty acids
TAGs come from diet, liver, storage deposits
Fats in the gut
A fatty meal - secretions from pancreas (lipases) and gall bladder (bile).
- bike salts (derived from cholesterol) act as detergents and emulsify fat in the gut.
Lipases release fatty acids from TAGs, cholesterol, esters and phospholipids.
Lipase- hydrolysis of eager bonds
Absorption of dietary fat
Smaller micelles of MAG, fatty acid, cholesterol, lysophospholipid and lipid- soluble vitamins are formed in small intestine.
Micelles/ lipids cross the epithelial cells by passive diffusion
TAGs are reformed in the small intestine cells o
Lipid transport: gut - liver
TAGs exit SI cells as chlyomicrons - complex micellar structure (lipoproteins) include proteins and cholesterol in a Plipid coat.
Travel via lymph to bloodstream approx 1 HR after a meal
Chlyomicrons circulate past the endothelial cells of the blood vessels.
TAGs are digested by lipoprotein lipase
Fatty acids released enter cells- used for energy or storage.
Chlyomicron remnants (coat) removed by the liver 5-8h after the meal
TAGs from synthesis in liver
Excess fatty acid and carbohydrate - TAGs
Export as very low density lipoprotein particles (VLDL)
= transport of TAGs to muscle and adipose tissue
VLDL- similar structure to chlyomicrons, different lipid composition, different proteins have cell- targeting signals p
Lipoprotein structure- lipid composition varies, app lipoproteins are recognised by receptors in target cells which can distinguish between HDL and VLDL
Assembly of VLDL in liver
Exported by the secretory pathway Synthesised on ER surface (apolipoproteins, TAGS and cholesterol ester cores, cholesterol and phosphatidyl choline coat) Assembly in the ER Maturation in the Golgi Packed in vesicles Secreted from cells
TAGs from stored fat
Stress (aerobic exercise, fasting)
Adrenaline (epinephrine) and glucagon release activates TAH lipase in adipose cells
Lipase removes fatty acids from stored TAHs and releases them into the blood
Fatty acids carried on serum albumin, circulate and taken up by cells for energy production via beta oxidation
