Chapter 9 - Lipids Flashcards
Hydrolyzable Lipids
Traiglycerols (fats and oils); waxes; glycerophospholipids; sphingolipids (spingophospholipids and sphingoglycolipids)
Assembled from various components - fatty acids combined with other groups: glycerol-based or sphingolipids
Non-hydrolyzable lipids
Steroids; eicosanoids; fat-soluble vitamins
cannot break down to simpler components
Palmitic Acid
C16:0
Stearic Acid
18:0
Oleic Acid
18:1 (9)
Linoleic Acid
18:2 (9, 12)
Alpha linolenic acid
18:3 (9,12,15)
Essential fatty acids
only obtained via diet (not produced)
Linoleate and linolenic acid
Role: precursors of prostalglandons, eicosanoids, epidermal lipids
membrane lipids
Tricylglycerols (TAGs)
3 fatty acyl residues esterfied to glycerol
Neutral and extremely nonpolar (great for energy storage!)
Anhydrous and highly reduced (major component of adipose tissue - tight packing)
Glycerophopholipids
highly amphipathic molecules: 2 fatty acids linked to glycerol-3-phosphate via ester linkages
Common polar head groups
ethanolamine, choline, serine
Plasmalogens
glycerol backbone
one ester-linked fatty acid
one vinyl-ether linked fatty acid
concentrated in CNS membranes; muscle, and peripheral nerve tissue
most common head group: choline or ethanolamine
possible function: protecs cell components from oxidative damage (free radicals) via vinyl ether linkage
Sphingolipids
sphingosine backbone (has amine); abundant in CNS of mammals
Steroid
Precursor: isoprenoid units and squalene
four fused rings, nearly planar structure, very hydrophobic
Cholesterol derivatives (features)
Cholesterol esters; bile salts; hormones; certain vitamins (solubility, rigidity, near planar shape)
Shape & functional group arrangement complementary to receptor, aid in digestion of lipids
Nonpolar allows it to get through membrane (some amphipathic)
signaling molecules, non-hydrolyzable, can mix and match rings to get new flavors
ex: stigmasterol (plant sterol); testosterone (steroid hormone); sodium cholate (bile salt); ergosterol (sterol from fungi and yeast)
fat soluble vitames (a, d, e) (a = retinol)
Cholesterol as related to membrane fluidity
Decreases membrane fluidity because its rigid steroid ring system interferes with the motions of the fatty acid side chains in other membrane liips
Fluidity of membranes as related to temperature
Fluidity is temp. dependent
At membrane “meltting point” -> transition from ordered crystalline state (gel) to fluid
Solid: Van der waals packing but free rotation; thicker due to stiff, extended tails
To maintain the fluid, dynamic structure: alter fatty acid content of membranes
Basic features and components of other fatty-acid based lipids
e.g. waxes, eicosanoids, and fat-soluble vitamins (some derived from cholesterol)
Waxes: esters of long-chain fatty acids and long-chain monohydroxide alcohols (insoluble in H2O; high mp)
protective waterproof coating on leaves, fruits, skin, etc
Eicosanoids: derived from arachindonic acid; oxygenate variations. Signal molecules: bind to enzymes or proteins for response
Fat-soluble vitamins: A (retinol), E (antioxidant), K (nonpolar lipids)
Functions of Lipids
energy storage, insulation, cushioning
cell compartmentalization
hormones and signaling
Melting Point
Effect of shorter tails and more double bonds
shorter tails - fewer van der waals interactions -> lower melting temp.
more double bonds- more kinking of fatty acid tail ->lower melting temp.
Sphingosine
C18 amino alchol: C1-OH; C2-NH2; C3-OH
Ceramindes
basis of all sphingolipids; fatty acyl group linked to C2 by an amide bond
Sphingomyelins
contains phosphate (only sphingolipid)
phophocholine or ethanolamine at ceramide C1
membrane component (about 10-20% of plasma membrane in lipids)
Cerbrosides and Gangliosides
carboyhydrate instead of phosphate at C1 (no phosphate)
Glycosphingolipids
complex
specific tissues and locations in cells
no phosphate, only carbohydrate linked to C1-OH
Cerbrosides
monosaccharide at C1 of ceramide (glucose, glactose, etc)
Gangliosides
ceramide with branched oligosaccharide at C1
lots of types found on cell surface about 6% of brain lipids
membrane signal and markers
problems with degradation responsible for Tay-Sach’s and similar diseases
Membrane Rafts
near crystalline regions rich in sphingolipids and cholesterol
polar head h-bond
cholesterol fills gaps between tails
more crytalline
entire raft diffuses laterally
Fluid Mosaic Model
olive-oil river, protein-filled treas, sugary skies
storm, crazy. Rafts appear and gone. Trees receive quick signals.
Ions whiz around and dive in and out of river.
Traffic is dizzy. Border is cell membrane. (50% of membrane is proteins)
Protein functions
signaling
communication
transport
metabolic rxns
membrane rearranging
Asymmetric distribution of membrane lipids
glycolipids and glycoproteins one extracellular face
asymmetry arises from lipid synthesis in the endoplasmic reticulum (plasma membrane in bacteria) by integral membrane proteins mostly on one face.
LIpid composition between leaflets modulated by..
enzyme activity
flippases: transport across membrane by facilitated diffusion
phospholipid traanslocases: active (atp driven) phospholipid transport across bilayer
non-random phospholipid distribution (communicates cell status or type)
Peripheral
soluble, globular proteins associated with membrane; dissociated by high ionic strenth or pH changes
Integral/intrinsic
inserted into or transverse membranes: removed by detergents or chaotropic agents
span membrane with an amino acid sequence specific to membrane proteins
Lipid-linked
covalent linkage to lipid group inserted into the membrane.
Alpha helix in membrane as transverse thing
satisfies all polar gorups with h-bonding
interacts favorably with nonpolar membrane interior
interactions between helices could be polar
Two distinct regions of integral proteins
region emerging from membrane: globular with hydrophobic core. Exterior of cell: modified with glycosylations. Interior of cell: polar with neg. and pos. charged regions
inside of membrane -> hydrophobic surface (few polar groups with associated H2O)
ex. Glycophorin
Hydropathy plot
identifies transmembrane helices in proteins
B-Barrel
possible polar interior/hydrophobic exterior
2-22 strands (max. H-bonding - satisfies polar backbone groups)
Barrel exterior (band of hydrophobic residues -interior of membrane)
hydrophobic band flanked by aromatic aa - interact with polar heads.
may be monomers or trimers
allow entry of small, polar molecules…can increase specificity by changing the residues.
Linkage of Peripheral protein to membrane surface
Noncovalent - h-bonds and charge-charge interactions
Covalent links from amino acids to lipids -> S, N, or O- linked to amino acids (ex. Cys, Lys, Ser)
