Lipid biochemistry: structural lipids Flashcards
1
Q
list some of the diverse functions of lipids (9)
A
energy storage, cell membrane components, enzyme cofactors, protein folding chaperones, electron carriers, light absorbing pigments, hormones, membrane anchors for proteins, intracellular messengers
2
Q
list 6 categories of lipids based on the chemical structure
A
fatty acids
glycerolipids
glycerophospholipids
sphingolipids
sterols
prenols
3
Q
what are fats and oils derivatives of
A
fatty acids
4
Q
describe the basic structure of a fat
A
carboxylic acid joined to a hydrocarbon chain
5
Q
how long is the hydrocarbon chain of a fatty acid (give a range)
A
4-36
6
Q
T or F: fatty acids are highly reduced
A
true
7
Q
what does it mean for a fatty acid to be highly reduced
A
they have lots of stored energy. they have lots of electrons that we are able to strip off
8
Q
describe the variation that the hydrocarbon chain of a fatty acid can have
A
can be long or short, branched or unbranched, saturated or unsaturated
9
Q
why do fats and oils make great energy storage molecules
A
the cellular oxidation of fatty acids into co2 and h2o is very exergonic (big energy release)
10
Q
what is a cis double bond
A
adjacent groups on the same side of the double bond
11
Q
what is a trans double bond
A
adjacent groups on different sides of the double bond
12
Q
what is a mono-unsat fatty acid
A
one with one double bond
13
Q
what is a poly-unsat fatty acid
A
one with two or more double bonds
14
Q
describe the shorthand way of naming fatty acids
A
length of carbon chain : number of double bonds (Δ^position of double bond)
15
Q
in naming fatty acids, 10 carbons =
A
deca
16
Q
in naming fatty acids, 12 carbons =
A
dodeca
17
Q
in naming fatty acids, 14 carbons =
A
tetradeca
18
Q
in naming fatty acids, 16 carbons =
A
hexadeca
19
Q
in naming fatty acids, 18 carbons =
A
octadeca
20
Q
in naming fatty acids, 20 carbons =
A
eicosa
21
Q
in naming fatty acids, 22 carbons =
A
docosa
22
Q
in naming fatty acids, 24 carbons =
A
tetracosa
23
Q
T or F: fatty acids usually have an odd number of carbons
A
false; they have an even number of carbons
24
Q
T or F: unless specified, assume naturally occurring fatty acids are in the cis conformation
A
true
25
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
26
how are omega fatty acids named
they're named in the reverse direction (starting at the methyl/omega end of the molecule)
27
describe the structure of omega 3 fatty acids
double bond at the 3rd to last carbon (from methyl end: C3=C4)
28
describe the structure of omega 6 fatty acids
double bond at the 6th to last carbon (from methyl end: C6=C7)
29
T or F: humans can synthesize omegas from enzymes
false; we cannot synthesize them, so they must be acquired from the diet
30
explain why omegas are considered essential
we must get them from the diet because we cannot synthesize them
31
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
32
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
33
why can't humans synthesize essential fatty acids?
humans lack the enzymes required to put double bonds near the methyl end of the molecule
34
in nature, how many carbons do FAs have
12-24
35
in nature, are FAs branched or unbranched
unbranched
36
in nature, what conformation are FA double bonds
cis
37
in nature, what is the location of a MUFA double bond
Δ9
38
in nature, what are the locations of the PUFA double bonds
Δ9,12,15
39
what is conjugation
when the bonds alternate between single and double
40
T or F: in nature, PUFAs are almost never conjugated
true
41
describe the solubility of fats in water
low but not zero
42
why is the solubility of fatty acids low but not zero
the carboxyl group is soluble but the rest isnt
43
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
44
would increasing the number of double bonds in the FA increase or decrease its solubility in water
increase
45
what is the consistency of saturated FAs at room temp
waxy (solid)
46
what is the consistency of unsaturated FAs at room temp
oily (liquid)
47
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
48
when is a saturated fatty acid the most stable? why?
when it's fully extended, because this minimizes steric hindrance
49
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
50
more VDW forces = more or less energy needed to disrupt the FAs?
more
51
more VDW forces = higher or lower melting point?
higher
52
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
53
describe how rancidity occurs
when you leave foods out, oxidative cleavage of unsat FAs occurs at the double bond
54
what is hydrogenation
turns natural cis unsat FAs into sat FAs (removes double bonds)
55
the downside of hydrogenation?
partial hydrogenation can also create trans double bonds = trans fats
56
describe the results of consuming trans fats
increase cardiovascular issues, raise bad blood cholesterol and lower good blood cholesterol, increase inflammation
57
what are waxes?
esters of long chain FAs with long chain alcohols
58
how long are the fatty acid chains in waxes?
14-36C
59
is the melting point of waxes high or low
high
60
is the solubility of waxes high or low
low
61
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
62
another name for triacylglycerols?
triglycerides (TAGs)
63
how many FA chains do TAGs have
3
64
what type of bond links the FA to glycerol in a TAG
ester
65
describe the polarity of TAGs
almost entirely non polar, as the polar OH group of glycerol is bound in an ester linkage
66
would a TAG be more or less soluble than a free FA
less soluble due to the carboxyl groups in ester bonds
67
describe the composition of TAGs in adipocytes
TAG fat droplets fill almost the entire cell, causing the nucleus to be pressed against the PM
68
function of adipocytes?
serve as reservoirs for metabolic fuel
69
why is it beneficial to have TAG storage under the skin
helps insulate hibernating animals or animals in cold climates
70
describe TAG storage in plants
TAGs are stored as oils in the seed, which provides energy + metabolic precursors during germination
71
T or F: both TAGs and glycogen can serve as stored energy
true
72
is energy storage mostly in TAGs or glycogen?
TAGs
73
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)
74
T or F: lipids are asymmetrically distributed across the two leaflets of the bilayer
true
75
T or F: all structural lipids are membrane lipids
false; TAGs are not membrane lipids, they are storage lipids
76
list the 5 membrane lipids
glycerophospholipids, sphingolipids, galactolipids, archaeal ether lipids, sterols
77
backbone for glycerophospholipids?
glycerol
78
what is the glycerol bound to in glycerophospholipids?
2 FAs and a head group
79
what type of linkages link the FAs to glycerol in glycerophospholipids
ester
80
what type of linkages link the head group to glycerol in glycerophospholipids
phosphodiester
81
are the head groups of glycerophospholipids polar or non polar
polar
82
T or F: in glycerophospholipids, one FA can sometimes be attached to the glycerol via an ether linkage
true
83
when would we see a glycerophospholipid FA attached to the glycerol via an ether linkage
in hearts of vertebrates
84
where are galactolipids located (which organism + which part of that organism)
thylakoid membranes in chloroplasts (in plants)
85
T or F: galactolipids have phosphate
false; they're phosphate free
86
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
87
describe the structure of galactolipids
can use 1 or 2 galactose residues as a head group, and there are 2 FA chains
88
galactolipids can make up __% of the total membrane lipids in plants
80%
89
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)
90
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
91
what is the backbone for sphingolipids
sphingosine, not glycerol
92
what type of groups does sphingosine have
amino and alcohol groups
93
how many carbons are in the sphingosine backbone
18
94
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
95
what does sphingomyelin contain in its head group
phosphate
96
T or F: sphingomyelin is both a sphingolipid and a phospholipid
true; sphingosine backbone and the head group contains phosphate
97
where is sphingomyelin found
myelin sheath of neurons
98
what is the net charge of sphingomyelin
no net charge
99
what type of head groups do glycosphingolipids have
sugar
100
what is a cerebroside
a glycosphingolipid with a single sugar head group and no net charge
101
what is a globoside
a glycosphingolipid with a multi sugar head group and no net charge
102
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
103
what gives a ganglioside its negative charge
a sialic acid sugar
104
where are gangliosides located in the body
on the surface of RBCs
105
what do the gangliosides on the surface of RBCs determine
blood type
106
T or F: all blood types have the same base
true
107
how many sugars comprise the base of every blood type
5
108
describe the structure of blood type O
just the base (5 sugars)
109
describe the structure of blood type A
extra acetylgalactosamine
110
describe the structure of blood type B
extra galactose
111
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
112
which bonds in glycerophospholipids are hydrolysable?
esters and phosphodiesters
113
which enzymes hydrolyze esters and phosphodiesters in glycerophospholipids
phospholipases
114
what does phospholipase A do
breaks ester bonds = releases one fatty acid from the glycerophospholipid
115
what do phospholipase C and D do
break phosphodiester bonds in the head group
116
how is Tay-Sachs disease caused
caused by a malfunctioning enzyme that can no longer cleave a ganglioside called GM2. = lipid accumulation
117
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
118
how many rings do sterols have
4
119
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
120
what sterols do animals have
cholesterol
121
what sterols do plants have
stigmasterol
122
what sterols do fungi have
ergosterol
123
what sterols do bacteria have
none! they can't synthesize it
124
how do sterols affect saturated fatty acids
they improve fluidity and prevent freezing, as sat FAs pack tightly together
125
how do sterols affect unsaturated fatty acids
they compact and constrain movement = prevent melting, as unsat FAs do not pack tightly
126
how are membrane rafts promoted
via sterols
127
what is a membrane raft
microdomains of the PM that are thicker than the rest, and they're enriched in cholesterol and glycosphingolipids
128
list 5 characteristics of membrane rafts
more cholesterol, more glycosphingolipids, longer acyl chains, saturated acyl chains, more lipid-anchored proteins
129
are membrane rafts common or uncommon? explain
common; they can cover up to half the membrane
130
how many lipids does a membrane raft usually have? how many proteins?
a couple of thousand lipids + 10-50 proteins
131
are proteins clustered or spread out in membrane rafts?
clustered
132
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
