what are lipids?
molecules that're soluble in fat, typically contain either long hydrocarbon chains (eg fatty acids) or multiple linked aromatic rings (eg steroids)
store energy in the body
main component of cell membranes
play role in many signaling pathways
what are fatty acids?
how are they differentiated?
type of lipid
have long hydrocarbon chain (C-H) w/ a carboxyl group (polar, acidic, COO-) at 1 end
1) number, location of double bonds
2) length of hydrocarbon chain
saturated vs. unsaturated fatty acid?
saturated: no double bonds btwn C-H
unsaturated: has some double bonds btwn C-H
how are fatty acids named?
# of carbon atoms:number of double bonds, Δ=positions of double bonds starting from COOH carbon
what causes a bend in hydrocarbon chain of fatty acids?
double bonds in fatty acids are in cis configuration
double bond causes bend
numbering of oleic acid?
numbering of alpha-linolenic acid?
18:3Δ9, 12, 15
numbering of arachidonic acid?
what is glycerol?
glycerol: 3-C sugar alcohol
how do glycerol + fatty acid come together?
what do they form? function of that structure?
ester of glycerol + fatty acid = glycerolipid
if all 3 OHs in glycerol are esterified, = triglyceride
triglycerides are energy stores in cells, present as fat droplets
what are glycerophospholipids or phosphoglycerides?
formed when 2 OH groups in glycerol are in etser linkages to fatty acids, 3rd is attached to a polar headgroup through a phosphate group
main component of plasma membranes
structure of glycerophospholipids?
2 OH groups of glycerol in ester linkages to fatty acids
3rd OH of glycerol attached to a polar head group thru a phosphate group
backbone = phosphatidic acid
most abundant examples have ethanolamine, choline, serine attached to phosphate group
most common glycerophospholipids in cell membrane?
has H as its X-group
what is structure of cephalin? where is it found?
has good insulating properties, so found in white matter of brain, spinal cord
has ethanolamine as X-group
structure of the plasma membrane?
lipid bilayer with hydrophobc fatty acid tails of phospholipds facing each other, polar head groups facing outward
thus functions as hydrophobc barrier btwn interior of cell and external environment
what is the function of phosphatidylinositol?
phospholipid where X group is a sugar
found on INNER LAYER of plsame membrane, where it binds molecules, gets phosphorylated, gets cleaved - so involved w/ specific cell-signaling pathways
what is cardiolipin?
member of phosphatidylinositol family
2 molecules of phosphatidic acid joined head-to-head by glycerol group
only found in inner mitochondrial membrane & chloroplasts of eukaryotes/prokaryotic membranes (NOT PLASMA MEMBRANE) where it transports electrons in e.t.c
what is this molecule?
where is it found?
found in mitochondrial membrane
what is the structure of a sphingolipid? what does this family of membrane lipids include?
sphingosine backbone w/ 2 long hydrocarbon chains, no phosphate group
includes: ceramide, sphingomyelin, glycolipids
what is the variable component of ceramide, in sphingomyelin, and in glycolipids?
glycolipids: mono- or oligosaccharide
what do defects in sphingolipid metabolism cause?
several types of inherited disorders called lysosomal storage diseases
glycolipids' main function?
energy storage in the body
have a carbohydrate group instead of phosphoryl group
sphingosolipids' main function in the body?
significant component of membranes
function of sphingomyelin?
significant component of lipid bilayer, usually inner layer
protects cell from mechanical and chemical interruption
what is tay sachs?
lipid storage disorder caused by mutations in sphingolipid metabolism w/ hexosaminidase enzyme
accumulation of gangliosides in nerve cells > becomes toxic to other pts of body > children die, by age 6
dx w/ white patch on the eye
what is the structure of cholesterol?
what is its fxn in plasma membrane?
multi-ring structure (steroid nucleus), hydrocarbon tail, hydroxyl group (polar pt of structure!)
increases impermeability of bilayer to small polar molecules, ie H2O
what is this?
see RIGID STRUCTURE makes cell plasma membrane very rigid
what is the nature of the distribution of lipids in the plasma membrane?
lipids' fxn determines if they're on inside or outside of membrane
which phospholipids are in which part of the plasma membrane, and why?
cytosolic side: PI (b/c precursor for signaling molecs), PS (monitors cell viability), PE
extracellular side: PC, sphingomyelin, glycolipids
in both monolayers: cholesterol
what does the presence of PS on the outer monolayer of the plasma membrane indicate?
indication that cell is undergoing apoptosis b/c PS monitors cell viability, usually is localized to cytosolic side of bilayer
what is membrane permeable to?
gases (CO2, O2)
hydrophobic molecules, like hydrocarbons (benzene)
what is membrane slightly permeable to?
small polar molecules (H2O, ethanol)
what is plasma membrane impermeable to?
large polar molecules, charged species (glucose, amino acids, ions)
what is the effect of increaisng the concentration of cholesterol in a membrane?
it decreases the permeability of the membrane to small polar molecules like water
b/c cholesterol is so rigid, does not allow passage
why does aspirin work?
aspirin is a weak acid
protonated form is uncharged
therefore can cross membrane by diffusion
what are the components of a plasma membrane?
ratio of these components?
both lipids and proteins
ratio of lipd to protein molecules is 50:1
what is meant by the "fluid mosaic" model of the plasma membrane?
because lateral diffusion in a membrane is so rapid, indicates that membrane is essentially a two-dimensional liquid
fluid nature of the plasma membrane allows cells to change shape rapidly w/o being ruptured
different ways proteins can be associated w/ membranes?
1) transmembrane proteins: cross out-inside
2) monolayer-associated: bind only to 1 layer of lipid bilayer
3) lipid-linked: bind to lipid assoc w/ membrane, but do not cross it
4) protein-linked: bind to a transmembrane protein
what are the 2 types of transmembrane proteins that contain regions that span the membrane?
1) alpha-helical type: eukaryotes
2) beta type: beta barrel, in prokaryotes - gram-negative bacteria, cell wall of gram-positive bacteria; in euk, only in outer membrane of mitochondria (and chloroplast)
what are integral membrane proteins
directly inserted into a lipid membrane or are covalently bound to other groups that're inserted in a membrane
or only inserted into inner leaflet of plasma membrane
attached to membrane thru covalent linkage to a fatty acid, hydrocarbon tail, phospholipid attachment
what are peripheral membrane protines
those associated w/ membrane thru non-covalent interactions w/ other proteins
what is the structure of alpha-helical transmembrane proteins?
1) hydrophobic side chains that interact w/ lipid bilayer
2) positive side chains to residues that interact w/ phospholipid head groups
3) positively charged residues in intracellular regions close to membrane, b/c inteact w/ particular lipidsin tehse regions
4) polar sidechains for transmembrane residues that face a polar channel
what are 3 major classes of lipids found in the plasma membrane?
how do their properties differ?
1) glycerolipids, store energy via fat droplets
2) glycerophospholipids, major cell membrane components
3) sphingolipids, also membrane lipids, but do not contain phosphate group
arachiodonic acid is named 20:4Δ5, 8, 11, 14. what do these numbers designate?
numbers designate the position of double bonds w/ respect to COOH end of hydrocarbon tail
why aren't triglycerides found in cell membranes?
all 3 of its OH groups are esterified, it does not have a polar head group, so it could not be a membrane component
what are some lipids that're differentially distributed in the plasma membrane?
describe the significance of this observation
asymmetric distribution in plasma membrane b/c of different function of each kind of lipid
PS (monitors cell viability), PI (signaling molecule) are negative, PE is neutral, are on cytosolic side of bilayer
PC, sphingomyelin, glycolipids are on extracellular side of bilayer
cholesterol is in both monolayers
what properties contribute to ability of molecules to cross membranes?
make up of membrane - so if only phospholipids or if also proteins
also partical itself- permeable gas and hydrophobic molecules pass easily; small polar molecules pass mostly easily; large polar molecuels and charged species cannot pass
discuss different ways in which proteins are associated w/ membranes
proteins can be components of plasma membranes
may be: transmembrane, monolayer-associated, lipid-linked, or protein-attached