Lipid biochemistry: structural lipids Flashcards
list some of the diverse functions of lipids (9)
energy storage, cell membrane components, enzyme cofactors, protein folding chaperones, electron carriers, light absorbing pigments, hormones, membrane anchors for proteins, intracellular messengers
list 6 categories of lipids based on the chemical structure
fatty acids
glycerolipids
glycerophospholipids
sphingolipids
sterols
prenols
what are fats and oils derivatives of
fatty acids
describe the basic structure of a fat
carboxylic acid joined to a hydrocarbon chain
how long is the hydrocarbon chain of a fatty acid (give a range)
4-36
T or F: fatty acids are highly reduced
true
what does it mean for a fatty acid to be highly reduced
they have lots of stored energy. they have lots of electrons that we are able to strip off
describe the variation that the hydrocarbon chain of a fatty acid can have
can be long or short, branched or unbranched, saturated or unsaturated
why do fats and oils make great energy storage molecules
the cellular oxidation of fatty acids into co2 and h2o is very exergonic (big energy release)
what is a cis double bond
adjacent groups on the same side of the double bond
what is a trans double bond
adjacent groups on different sides of the double bond
what is a mono-unsat fatty acid
one with one double bond
what is a poly-unsat fatty acid
one with two or more double bonds
describe the shorthand way of naming fatty acids
length of carbon chain : number of double bonds (Δ^position of double bond)
in naming fatty acids, 10 carbons =
deca
in naming fatty acids, 12 carbons =
dodeca
in naming fatty acids, 14 carbons =
tetradeca
in naming fatty acids, 16 carbons =
hexadeca
in naming fatty acids, 18 carbons =
octadeca
in naming fatty acids, 20 carbons =
eicosa
in naming fatty acids, 22 carbons =
docosa
in naming fatty acids, 24 carbons =
tetracosa
T or F: fatty acids usually have an odd number of carbons
false; they have an even number of carbons
T or F: unless specified, assume naturally occurring fatty acids are in the cis conformation
true
describe the systematic naming system of fatty acids
count the number of carbons and get the corresponding name, count the number of double bonds and get the corresponding name, and then determine the conformation and position of the double bonds
cis/trans - double bond position - systematic name
how are omega fatty acids named
they’re named in the reverse direction (starting at the methyl/omega end of the molecule)
describe the structure of omega 3 fatty acids
double bond at the 3rd to last carbon (from methyl end: C3=C4)
describe the structure of omega 6 fatty acids
double bond at the 6th to last carbon (from methyl end: C6=C7)
T or F: humans can synthesize omegas from enzymes
false; we cannot synthesize them, so they must be acquired from the diet
explain why omegas are considered essential
we must get them from the diet because we cannot synthesize them
explain why we need essential fatty acids (3)
- they’re integral parts of cell membranes and affect function of membrane receptors
- they’re parts of hormones that regulate blood clotting, contraction and relaxation of artery walls, and inflammation
- they’re highly concentrated in retinal membranes and in grey matter membranes
list 4 things that deficiencies in essential fatty acids can result in
- decreased growth in infants
- poor wound healing
- poor neuron growth, synapse formation, synaptic plasticity
- vision problems
why can’t humans synthesize essential fatty acids?
humans lack the enzymes required to put double bonds near the methyl end of the molecule
in nature, how many carbons do FAs have
12-24
in nature, are FAs branched or unbranched
unbranched
in nature, what conformation are FA double bonds
cis
in nature, what is the location of a MUFA double bond
Δ9
in nature, what are the locations of the PUFA double bonds
Δ9,12,15
what is conjugation
when the bonds alternate between single and double
T or F: in nature, PUFAs are almost never conjugated
true
describe the solubility of fats in water
low but not zero
why is the solubility of fatty acids low but not zero
the carboxyl group is soluble but the rest isnt
would increasing the length of the FA chain increase or decrease its solubility in water? why?
decrease because less of the molecule would be soluble
would increasing the number of double bonds in the FA increase or decrease its solubility in water
increase
what is the consistency of saturated FAs at room temp
waxy (solid)
what is the consistency of unsaturated FAs at room temp
oily (liquid)
describe van der waals forces
electrons in an orbital are distributed asymmetrically and give a small charge to the atom. If atoms are precisely positioned apart, these small transitory charges can attract one another
when is a saturated fatty acid the most stable? why?
when it’s fully extended, because this minimizes steric hindrance
describe the behavior of extended sat fatty acids in regards to van der waals forces
extended sat FAs pack tightly together, close enough to maximize van der waals interactions. More VDW interactions = more thermal energy required to disrupt the FAs and a higher melting point
more VDW forces = more or less energy needed to disrupt the FAs?
more
more VDW forces = higher or lower melting point?
higher
describe VDW forces in regards to unsat FAs
unsat FAs have kinks that prevent tight packing = less VDW forces = less thermal energy required to disrupt the FAs = lower melting point
describe how rancidity occurs
when you leave foods out, oxidative cleavage of unsat FAs occurs at the double bond
what is hydrogenation
turns natural cis unsat FAs into sat FAs (removes double bonds)
the downside of hydrogenation?
partial hydrogenation can also create trans double bonds = trans fats
describe the results of consuming trans fats
increase cardiovascular issues, raise bad blood cholesterol and lower good blood cholesterol, increase inflammation
what are waxes?
esters of long chain FAs with long chain alcohols
how long are the fatty acid chains in waxes?
14-36C
is the melting point of waxes high or low
high
is the solubility of waxes high or low
low
describe some of the diverse functions of waxes
- used by plankton as main energy source instead of TAGs
- birds secrete waxes from skin glands to keep feathers water repellent
- plants secrete waxy cuticle around leaves to prevent water loss
- worker bees secrete wax to help make the honeycomb
- used in lotions, polishes, shampoos, etc
another name for triacylglycerols?
triglycerides (TAGs)
how many FA chains do TAGs have
3
what type of bond links the FA to glycerol in a TAG
ester
describe the polarity of TAGs
almost entirely non polar, as the polar OH group of glycerol is bound in an ester linkage
would a TAG be more or less soluble than a free FA
less soluble due to the carboxyl groups in ester bonds
describe the composition of TAGs in adipocytes
TAG fat droplets fill almost the entire cell, causing the nucleus to be pressed against the PM
function of adipocytes?
serve as reservoirs for metabolic fuel
why is it beneficial to have TAG storage under the skin
helps insulate hibernating animals or animals in cold climates
describe TAG storage in plants
TAGs are stored as oils in the seed, which provides energy + metabolic precursors during germination
T or F: both TAGs and glycogen can serve as stored energy
true
is energy storage mostly in TAGs or glycogen?
TAGs
why is energy storage mostly in TAGs (3)
- there is limited space for glycogen storage in the liver and muscles. TAG storage is much more available
- TAGs are not hydrated, so it doesn’t come with water weight
- TAGs store more J/gram of energy (they’re more heavily reduced)
T or F: lipids are asymmetrically distributed across the two leaflets of the bilayer
true
T or F: all structural lipids are membrane lipids
false; TAGs are not membrane lipids, they are storage lipids
list the 5 membrane lipids
glycerophospholipids, sphingolipids, galactolipids, archaeal ether lipids, sterols
backbone for glycerophospholipids?
glycerol
what is the glycerol bound to in glycerophospholipids?
2 FAs and a head group
what type of linkages link the FAs to glycerol in glycerophospholipids
ester
what type of linkages link the head group to glycerol in glycerophospholipids
phosphodiester
are the head groups of glycerophospholipids polar or non polar
polar
T or F: in glycerophospholipids, one FA can sometimes be attached to the glycerol via an ether linkage
true
when would we see a glycerophospholipid FA attached to the glycerol via an ether linkage
in hearts of vertebrates
where are galactolipids located (which organism + which part of that organism)
thylakoid membranes in chloroplasts (in plants)
T or F: galactolipids have phosphate
false; they’re phosphate free
why is it important that galactolipids are phosphate free
phosphate can be limiting in the soil, so plants using galactolipids allows them to conserve their phosphate
describe the structure of galactolipids
can use 1 or 2 galactose residues as a head group, and there are 2 FA chains
galactolipids can make up __% of the total membrane lipids in plants
80%
how do archaeal membranes survive such extreme environments
extra long hydrocarbon chains and they use ether linkages (which are more stable than esters at higher temps)
describe the structure of archaeal ether-linked lipids
lipids are long and have branched hydrocarbon chains. They’re 2x the length of regular glycerophospholipids, and they span the entire length of the bilayer. CH chains are ether linked to glycerol on BOTH ends, and each glycerol has a head group attached
what is the backbone for sphingolipids
sphingosine, not glycerol
what type of groups does sphingosine have
amino and alcohol groups
how many carbons are in the sphingosine backbone
18
describe the structure of a sphingolipid
the long hydrocarbon chain of sphingosine is analogous to one fatty acid. Only one FA will bind to sphingosine via an amide linkage. The final glycerol-analogous carbon attached to a head group
what does sphingomyelin contain in its head group
phosphate
T or F: sphingomyelin is both a sphingolipid and a phospholipid
true; sphingosine backbone and the head group contains phosphate
where is sphingomyelin found
myelin sheath of neurons
what is the net charge of sphingomyelin
no net charge
what type of head groups do glycosphingolipids have
sugar
what is a cerebroside
a glycosphingolipid with a single sugar head group and no net charge
what is a globoside
a glycosphingolipid with a multi sugar head group and no net charge
what is a ganglioside
a glycosphingolipid with a multi sugar head group and at least one sialic acid sugar to provide a negative charge at pH 7
what gives a ganglioside its negative charge
a sialic acid sugar
where are gangliosides located in the body
on the surface of RBCs
what do the gangliosides on the surface of RBCs determine
blood type
T or F: all blood types have the same base
true
how many sugars comprise the base of every blood type
5
describe the structure of blood type O
just the base (5 sugars)
describe the structure of blood type A
extra acetylgalactosamine
describe the structure of blood type B
extra galactose
what will happen when you receive blood with a different sugar head group
it will be recognized as foreign and be attacked by the immune system
which bonds in glycerophospholipids are hydrolysable?
esters and phosphodiesters
which enzymes hydrolyze esters and phosphodiesters in glycerophospholipids
phospholipases
what does phospholipase A do
breaks ester bonds = releases one fatty acid from the glycerophospholipid
what do phospholipase C and D do
break phosphodiester bonds in the head group
how is Tay-Sachs disease caused
caused by a malfunctioning enzyme that can no longer cleave a ganglioside called GM2. = lipid accumulation
describe what happens when GM2 cannot be cleaved (during Tay-Sachs disease)
it’s found int he nervous system, so the inability to degrade it will affect neuron function
GM2 deposits will accumulate in lysosomes –> loss of motor skills, muscle weakness, growth in head size, lack of response to surroundings (shows at 3-6 months of age)
blindness, paralysis, death by 3-4 years old
how many rings do sterols have
4
describe the structure of the rings in a sterol molecule
there are three 6C rings and one 5C ring. The rings are fused together. The molecule is very rigid and planar, with little rotation around C-C bonds
what sterols do animals have
cholesterol
what sterols do plants have
stigmasterol
what sterols do fungi have
ergosterol
what sterols do bacteria have
none! they can’t synthesize it
how do sterols affect saturated fatty acids
they improve fluidity and prevent freezing, as sat FAs pack tightly together
how do sterols affect unsaturated fatty acids
they compact and constrain movement = prevent melting, as unsat FAs do not pack tightly
how are membrane rafts promoted
via sterols
what is a membrane raft
microdomains of the PM that are thicker than the rest, and they’re enriched in cholesterol and glycosphingolipids
list 5 characteristics of membrane rafts
more cholesterol, more glycosphingolipids, longer acyl chains, saturated acyl chains, more lipid-anchored proteins
are membrane rafts common or uncommon? explain
common; they can cover up to half the membrane
how many lipids does a membrane raft usually have? how many proteins?
a couple of thousand lipids + 10-50 proteins
are proteins clustered or spread out in membrane rafts?
clustered
what is the benefit to clusters of proteins within membrane rafts?
proteins are more likely to interact if they’re isolated on the same raft
