Lipids and membranes Flashcards
what are the 2 common properties that lipids share?
- insolubility in aqueous or water based solutions
2. solubility in organic or non-polar solvents
when you increase the number of C in a lipid, what happens to solubility?
inc # C = dec solubility = molecule will e bigger = more van de waals interactions holding it together
what are the 5 biological functions of lipids?
- storage of energy:
- reduced compounds (high available energy)
- hydrophobic nature (good packing) - membrane structure
- main component - signaling molecules
- hormones (steroids)
- vit A and D (hormone precursors - cofactors for enzymes
- vit K: blood clot formation - Antioxidants:
- vit E: protects membranes (membranes are easily damaged by free radicals)
what are the two types of lipids? major difference?
- complex lipids (has FA)
2. biologically active lipids (no FA but are derived from FA)
what are the 2 types of complex lipids?
polar or non polar?
storage (non polar)
structural (polar)
2 types of storage lipids?
polar or non polar?
triglycerides and waves
nonpolar
2 types of structural lipids?
polar or non polar?
phospholipids
sphingolipids
polar
2 types of biologically active lipids?
prostaglandins
steroids
structure of a fatty acid?
amphipathic molecules
3-35 C hydrocarbon chains
carboxylic acid group
general chemical formula: CH3 (CH2)n COOH
n= or > than 2
describe FA waxy solids at room temp
FA with c10 or higher
saturated hydrocarbon chains
describe FA oily liquids at room temp
FA with c9 or lower
saturated of unsaturated hydrocarbon chains
how to name FA?
describe structure of 18:2 (delta 9,12)
refer to table 10-1
18 carbons. 2 double bonds at 9th and 12th carbon
what is the pKa of the COOH group on fatty acids?
what affects the pKa in FA?
pH of fully ionized FA?
less than 5
lower pKa means stronger acid. COOH group will have lower pKa (or higher acidity) if R group is very EN = low electron density on H because electrons are pulled towards the R group
fully ionized FA is pH 7
do natural FA have even or odd number of C?
even number
are natural FA branched or un-branched?
un-branched
what are the effects of saturation or unsaturation of a FA
3 main physical property changes?
ie. why is saturated FA solid at room temp?
double bonds (from unsaturation) affects the positions of FA tails
DB produces kinks therefore:
1. sat FA are more packed than un-sat
2 less ordered packing leads to weaker intermolecular interactions (van der waal)
3. lower mp for unsat FA
what is numbered carbon #1 in FA?
numbering starts with the COOH end
what defines the physical properties are FA?
physical properties (solubility and mp) are defined by:
- hydrocarbon chain length
- degree of saturation
how is solubility and mp affected with an increase in chain length of a FA?
effects in decrease in degree of saturation in a FA
when chain length increases, solubility in water decreases (becomes more nonpolar) and mp increases (higher van der waals)
decrease in deg of sat = become more unsaturated = add more DB
- more DB = less ordered packing = water intermolecular interactions = takes less thermal energy to melt = lower mp
- also more DB = less packed
what essential FA can humans not produce?
- linoleic acid (omega 6)
2. linolenic (omega 3)
what does omega 3 FA inhibit?
formation of thromboxane (an eicosanoid) required for platelet aggregation and clot formation.
what are the 3 major types of omega 3 FA ingested in foods?
what happens to them once eaten?
which 2 are the effective PUFAs?
alpha-linolenic (ALA)
eicosapentaenoic acid (EPA)
docosahexaenoic acid (DHA)
once eaten, the body converts ALA to EPA and then to DHA. Thus effective PUFAs are EPA and DHA
describe formation of trans FA.
describe rigidity of trans FA
-form by partial hydrogenation of unsat FA and cis-DB isomerization to trans-DB
- DB can rotate like SB = increased rigidity in the molecule.
- results in reduced membrane fluidity, flexibility and function
describe formation and structure of acylglycerols
- results from condensation rxns between one glycerol sugar with one, two or three FA.
- glycerol (backbone) and FA are linked by an ester linkage
- triacylglycerol has a center of asymmetry (chiral carbon) at the 2nd C atom
- most abundant form of metabolic storage lipids in animal and plant cells (energy storage and rapid source of energy))
- can be present as insoluble forms
- animal triglycerides are solid. plant and fish triglycerides are oil at room temp
simple vs mixed/complex triglycerides?
if all FA are the same length = simple triacylglyceride (has no chiral carbon)
if all FA have different lengths and degree of saturation = mixed/complex tracyglyceride (has a chiral carbon)
are animal, plant, fish triglycerides solid or liquid at room temp?
animal: solid
fish and plants: liquid
advantage of fats over polysaccharides?
acylgycerides carry more energy per carbon because they are more reduced
FA carry less h20 because they are nonpolar
describe the different energy use of glucose vs acylglycerides
glucose: (glycogen)
- short-term energy needs
- quick energy delivery
acylglycerides:
- long term energy needs
- good storage
- slow delivery
how are triacylglyerols and monoacylglycerols digested?
conversion to lipoproteins
in the small intestine
by enzyme pancreatic lipase
monoacylglyerols:
- absorbed by intestinal cells
- converted to triacylglyerols
- assembled into lipoproteins
what happens when you treat tri-acylglcerol with strong base of acid?
hydrolysis of the ester bond between glycerol and FA
ie. soap
how are waxes formed?
describe role of waxes
condensation reaction between long FA and alcohol hydrocarbon chains
act as metabolic fuel and water impermeable coating
structure of waves? how are they broken down?
DON’T contain glycerol
broken down with strong acids and bases to FA and alcohol hydrocarbons
have higher melting temp than tri-acylglycerides (because long hydrocarbon chains)
what are functions of structural lipids?
2 types?
- membrane function
- cell signalling
phospholipid and sphingolipids
describe phospholipids
basic unit of phospho-acylglycerol?
structure?
- one of major components of cell membranes
- phosphatidic acids are neg charged at pH7 andis the basic unit of phospho-acylglyerol
structure of phospho-acylglycerol:
- made up of 1,2-diaclglycerol ( 2 FA plus glycerol) linked to phosphoric acid
- 2 FA are linked to 1st and 2nd OH of glycerol by ester bonds
- 1st FA is usually saturated, 2nd FA is unsaturated (kink)
- phosphoric acid is linked to 3rd OH of glycerol by phospho-ester bond
- head groups: alcohol based compounds linked to phosphatidic acids
-refer to diagram
chirality of glycerophospholipid?
chirality of glycerol?
glycerol: not chiral on it’s own ( has symmetry through C2)
how many chiral centres in glycerophospholipid?
2
what determines physical properties (and surface properties of membranes) of glycerophospholipid?
head group (X)
different organisms and different tissues have different lipids head groups
what is the major component of most eukaryotic cell membranes?
phosphatidylcholine
X (head group) is choline
net charge of zero
prokaryotes can’t synthesize this = their membranes don’t contain it
describe the charge of glycerophospholipids
amphipathic (hydrophillic and phobic)
head group is charged (phillic)
FA are phobic
what bond is used in the glycerophospholipid between the head group and glyercol backbone?
phosphodiester linkage
what gives cell membranes their overall positive or negative surface charges?
distribution of glycerophospholipids
describe sphingolipids:
what is the backbone?
type of linkages?
subclasses?
- backbone is a long chain amino alcohol sphingosine (NOT glycerol)
- FA attaches to sphingosine (amide linkage) at C2 of spingosine chain
one FA + sphingosine = ceramide (structurally similar to diacylglycerol)
polar head group is attached to C1 by a glycosidic or phosphodiester bond
subclasses (determined by head group)
- phosphoryl choline + spingosine = sphingomyelin
- sugar group + sphingosine = cerebroside
- combination of sugars (or oligosaccharide) + sphingosine = ganglioside
refer to diagram
-know which parts are FA spingosine, amide link,
where are sugar containing glycosphingolipids found?
outer face of plasma membranes
easily detectable by the immune system.
targets specific tissue membranes
nonpolar FA on inside
neg OH on outside
what determines blood groups?
what determines the structure of sugar on head group in glycosphingolipids?
type of sugar located on head groups in glycosphingolipids
determined by expression of specific glycosyltransferases
- inactive glycosyltransferase: has O antigen
- glycosultransferase that transfers N-acetylgalactosamine group: has A blood group
- glycosyltransferase that transfers galactose: B group
what bond is inbetween polar head groups of phospholipids and glycolipids?
phospholipids: phosphodiester bond
glycolipids: glycosidic link
- linkage between FA in triacylglyceroles, glycerophospholipids, galactolipids, and sulfolipids?
- in sphingolipids?
- ester link
2. amide link
describe biologically active lipids?
2 major classes?
dont contain FA or glycerol backbone
can be generated from FA
occurs in smaller amounts in cells and tissue
role: recruit other cellular proteins to function
classes:
1. prostaglandins: generated through modification of FA
- sterols: generated from 2C (acetate) and through modification of other sterols
why are steroids important?
digestion: bile salts act as fat solubilizers
hormones: human sex hormones
what are the 4 types of phospholipases?
how do they differ?
4 types
1. phospholipase A1: cleaves C1 ester linked FA
- PPL A2: cleaves C2 ester linked FA
- PPL C: cleaves C3 phosphoester linked phosphoric acid
- PPL D: cleaves phosphoesterlinked X or head groups
(refer to diagram)
PPL differ by where they cleave the ester linkage
-don’t cleave ethyl linkages as in sphingosine
2 classes of phospholipases?
- phospholipid specific lipases
2. broad substrate phospholipases
role of phosphatidylinosital 4,5-bisphospahte?
example. maybe not important for final
found on intracellular side of cell membrane
hydrolysis is important for signalling pathway (protein kinase C)
role of paracrine lipid hormone?
vital for signaling molecules
enzymatic oxidation of arachidonic acid yields:
prostaglandins
thromboxanes
leukotrienes
3 products of enzymatic oxidation of arachidonic acid?
example. potentially not important
prostaglandin: inflammation and fever. smooth muscle contraction in uterus
tromboxane: vasoconstrictor. platelet aggregation:
Leukotriene: smooth muscle contraction in lungs
function of cholesterol:
prevents close packing of lower end of the FA hydrocarbon = decreases mp of lipid bilayer
promotes tight packing of the upper ends of the FA hydrocarbon tails = increases mp of bilayer
sterol structure?
3 parts:
- four fused rings. rigid and planar. hydrophobic
- flexible and branched hydrocarbon/alkyl side chain
- OH polar head
amphipathic molecule (acts as structural lipid)
how does cholesterol accumulate in membrane?
cholesterol rigid structure favours interaction with saturate/transfat/unsat lipid
how is cholestrol a fluidity buffer?
describe gel and liquid crystalline phases?
prevents sudden change in pH. avoids sudden gel to crystal phase
allows membrane to tolerate changes in temperature without losing property
gel phase:fully extended and packed hydrocarbon chains
liquid phase: disordered and fluid chains
refer to chart (slide 348): cholesterol creates slower rate of change when temp increases
what are lipid aggregates?
3 possible structures?
- lipid micelles
- small spherical
- h2o excluded from interior
- head to tail ratio > 1
- free FA and detergents favour this conformation
ie. soap - lipid bilayer
- 2 monolayer
- sheet like structure
- water is excluded from interior
- head to tail ratio = 1
- phosphoacylglycerides and sphingolipids favors this - liposomes
- derived from lipid bilayer, folded back onto itself
- encloses water on interior. acts as barrier between 2 environments
can storage lipids form micelles?
no they are completely NP
can detergents form micelles?
yes
most detergents have polar head, charged group and rest is hydrophobic
what do storage lipids form in aqueous solutions?
lipid droplets (they are NP)
what is the cell membrane impermeable and permeable to?
impermeable: charged ion and large molecules or proteins
permeable: hydrophobic molecules, neutral gases, h2o
what was the black membrane experiment used for?
used to determine what solutes cross the lipid bilayer down their electrochemical gradients
layers of the cell membrane?
3 layers. 2 electron dense layers (inner and outer surfaces)
total: 5mn thick
3. 5-4nm of the middle hydrocarbon layer
how can lipid molecules move on the cell membrane?
enzymes for catalyzed flip-flops?
- diffuse laterally
- spin on axis
no uncatalyzed flip-flop motion
catalyzed flipflop enzymes:
- flippases (uses ATP)
- floppases (uses ATP)
- scramblase (no ATP)
are are membrane lipids distributed between inner and outer leaflets?
asymmetrically
membranes of different cell organelles have different…
lipid composition
cell membranes have many globular proteins where the phospholipids act as…
solvent
3 classes of membrane proteins?
- integral or intrinsic MP: transverse bilayer one or several times. Can be extracted from membrane with detergents
- anchored MP: inked covalently to FA in inner or outer leaflet (don’t transverse bilayer entirely). Detergent can extract from the membrane
- peripheral/associated MP: associates or interacts with transmembrane protein. (don’t transverse bilayer)
