Lipids Flashcards
what are complex lipids
built on smaller components, to form a complex that is a lipid
e.g. phospholipids
most common in nature
major component = fatty acid
what is a simple lipid?
make up a smaller proportion in nature
have a specific function
e.g. cholesterol
fatty acids?
RCOOH
- carboxyl group (pKa of about 4.5, ionised at most pH)
R - long chain hydrocarbon
key points of carboxyl group of fatty acids?
when are fatty acids ionised?
has a charge distribution
has available electron pairs - form hydrogen bonds with water
R group is hydrophobic
since most cells operate in aqueous env, fatty acids tend to be ionised in most situations
key points about R group of fatty acids?
how does this affect grouping of molecules?
hydrophobic
can be saturated/ unsaturated
most double bonds are cis - cause kink in chain
hydrophobic chains want to group together and exclude water - how they do this is dependent on shape (determined by double bonds)
systematic names of fatty acids?
end in ‘oic acid’ or ‘oate’ if in ionised form
double bonds indicated by a number
cis-9-hexanoic acid
shorthand of fatty acids
C17:1 Δ10
C20:4 Δ2, 5, 6, 18
17 carbons , with 1 double bond at position 10
how do fatty acids come together to form triacylglycerols?
each fatty acid is attached by ester linkages to the 3C glycerol backbone
fatty acid chain referred to as acyl
R groups of each fatty acid will normally be different
structure of complex lipids - phospholipids
2 fatty acid chains
1 polar ‘head’ group - can itself be attached to a number of different groups (signified as X)
more of a structural than storage role
what increases melting point of lipids?
longer chain length = more interactions
fewer double bonds = molecule can pack more closely together
chain length/ number of double bonds will affect the properties of a membrane
fluidity of membranes?
unsaturated fatty acids prevents them from packing as closely together and increases membrane fluidity
unsaturated fatty acids at lower temp = prevent crystallisation
which lipid molecules are amphipathic?
phospholipids, glycolipids, sphingolipids and ceramides
NOT triacylglycerols
what happens when you mix amphipathic molecules in water?
hydrophillic part tries to get into water
hydrophobic part tries to get away from water
- can form monolayer or bilayer
how do micelles form
vigorous shaking of monolayer
close packing of hydrocarbon tails excluding water leads to an increase in entropy (reduce SA exposed to water, so the molecules previously ordered around them are released and free to move)
how do liposomes form?
from the vigorous shaking of bilayers
same as micelles, but much larger
what do triacylglycerols form?
form fatty droplet inside the cell
higher carbon density
pack closely to avoid water - concentrated energy store
where do fatty acids that are metabolised into ATP come from?
- diet (30-40% of calories)
- adipose tissue - fat storage cells (store triacylglycerols)
- de novo synthesis - form CH and AA
role of liver in fatty acid metabolism
produces bile (bile salts/ acids that are derived from cholesterol)
begins to collect in hepatic duct
stored in gall bladder
acts as a detergent/ stabilising agent - emulsify lipid into smaller fat droplets (micelles)
role of pancreas in lipid metabolism?
produce digestive enzymes and bicarbonate solution (raise pH of stomach contents)
lipases aid fat digestion
how are pancreas and liver attached to stomach
bile duct and pancreatic duct share the opening to the small intestine
pathway of metabolism of triacylglycerols
mix with bile salts - micelles
increases SA for lipases to act
triacylglycerols -> 2 FA and a monoacylglycerol
(these are hydrophobic - not favour aq environment)
move into intestinal epithelial cell down CG (maintained by uptake of monoacylglycerols and FA into ER)
reformed as triacylglyercols
packed into small MB vesicles =chylomicrons
exocytosed into lymphatic vessel, and eventually enters blood
