unit 15: Cell membranes Flashcards
what are the functions of lipids in animals?
provide structure in cell membranes
energy storage
metabolites and messengers
enzyme cofactors
pigments (light retinal pigments, photosynthetic pigments)
what are the three main types of animal membrane lipids and their components?
- phospholipids (glycerophospholipids, sphingophospholipids)
- glycolipids (glycosphingolipids)
- sterols (cholesterol)
what are the general features of fatty acids
- can have varying lengths of hydrocarbon chains w/ terminal COOH group
- usually even number of carbon atoms in cellular fatty acids
- can be saturated or unsaturated. and varying degrees of saturation
describe the general features of sterols
- a 4 ring hydrocarbon structure w/ different hydrocarbon tails
- has a OH- group (equivalent to a polar head group)
- is only produced by eukaryotes
what are the main functions of membranes
- enclose cell (plasma membrane)
- intracellular compartmentalization (internal membranes in eukaryotes)
- controls flow of molecules. between inside and outside of cell and intracellular compartments
- ATP synthesis: occurs in plasma membrane of prokaryotes, inner mitochondrial membrane/chloroplast thylakoid membrane of eukaryotes
- cell adhesion
- cell communication/signaling
composition and fundamental architecture of cellular membranes
- double-layered sheet like structures (leaflets) about 5-10 nm thick
- composed mainly of lipids and proteins.
- some carbohydrates can be attached
- 1:4 to 4:1 lipid: protein ratio
- non covalent assemblies of phospholipids stabilized by non covalent forces
- asymmetric composition
- electrically polarized. usually negative inside. the membrane potential is about 60mV
- fluid mosaic model
- dynamic
how do lipids interact with water and the forces contributing to formation of membranes
- lipid bilayers form through self assembly of phospholipids via non covalent forces
- driven by hydrophobic effect and van Der Waals forces b/w acyl chains
- stabilized by interaction of hydrophilic head groups w/water. this is electrostatic interactions and hydrogen bonding
- cooperative structures can be extensive
- self healing structures: energetically unfavorable when planar. becomes energetically favorable when membranes fuse.
rank the permeability of gases, small uncharged polar molecules, large uncharged polar molecules, ions, charged polar molecules
gases - permeable
small uncharged polar molecules- slightly permeable
large uncharged polar molecules- impermeable
Ions- impermeable
charged polar molecules- impermeable
what are the categories of membrane proteins
peripheral membrane proteins
lipid-anchored proteins
integral membrane proteins
describe peripheral membrane proteins
- electrostatic interaction and H-bonding w/polar head groups and other proteins
- easily dissociated by ph, salt
describe integral membrane proteins
- usually span membrane
- hydrophobic domains interact w/hydrophobic core
- hydrophilic domains interact w/surface
- require detergents for disociation
describe lipid-anchored proteins
- covalently attached hydrophobic chain provides membrane anchor
what are the different motifs found in membrane-spanning domains of integral membrane proteins
- single pass transmembrane protein
- multi pass transmembrane proteins
- beta strand transmembrane proteins
describe single pass transmembrane protein
a-helix
oligomerization by coiled-coil formation
hydrophobic amino acid side chains protrude from helix:
van der Waals interactions w/ lipids
peptide bonds toward interior of helix
describe multi pass transmembrane proteins
- several a-helices
- bacteriorhodopsin: proton pump, similar to eukaryotic G-coupled protein family, 7 membrane spanning helices connected by loops
- eukaryotic aquaporins: facilitate diffusion of small hydrophilic molecules, half-helices form channel, tetramers w/ several membrane-spanning domains
describe b-strand transmembrane proteins
b-barrel motif formed by H-bonds between neighboring antiparallel beta-strands
- non polar residues outside
- polar residues line interior
describe a method for prediction of certain motifs
hydropathy plot:
- identifies segments w/hydrophobic amino acids from primary seq.
- plots free energy change for transferring 20 amino acid segments from hydrophobic to aqueous environment
- useful for predicting a-helical transmembrane domains
what effect do ionic detergents have on membrane proteins
- bind to hydrophobic regions of proteins (membrane or soluble proteins)
- denature proteins at high concentration
what effect do non-ionic detergents have on membrane proteins
- milder non-denaturing
- solubilize membrane proteins at low concentration
- solubilize membranes by micelle formation at high concentration
define lipide/lipodomics
Complement of lipid-containing molecules of a cell/organ/tissue and its analysis
describe unsaturated fatty acids
- cis configuration of double bonds in natural FA
- double bonds are usually separated by one or more methylene groups in polyunsaturated fatty acids
- have a lower melting point compared to saturated FA (ex. steric acid has a higher mp than oleic acid)
what are methylene groups
CH2
why are fatty acids a good source of energy?
they are highly reduced, more than carbs. so they are electron rich
- this means they can provide a lot more energy than carbs
what do membrane lipids contain
polar head group and non polar tail
membrane lipids are___
amphiphilic, meaning they contain both polar and non polar portions
contrast phospholipids and glycolipids
phospholipids:
- contain a phosphate group
- can have a glycerophospholipids/phosphoglycerides or sphingolipid/ sphingophospholipid
glycolipids:
- contain a carbohydrate
- can have sphingolipid or galactolipid
describe glycerophospholipids
glycerol attached to
- 2 FA
- Phosphate - alchohol
describe sphingolipids
phospholipid:
sphingosine backbone
- 1 FA
- Phosphate - alcohol
glycolipid:
sphingosine backbone
- 1 FA
- carbohydrate portion
galactolipids
glycerol backbone
- 2 FA
- carbohydrate
describe phosphatidic acid
- precursor glycerophospholipids/ Phosphogylcerides
- is just the phosphate group, no alcohol bound
- small amount found in membranes
- glycerol backbone; C1 and C2 are ester to FA one usually has a cis double-bond. C3 ester bound to the phosphate group
in phosphoglycerides the phosphatidate is ester bound to an alcohol
what are common alcohols in glycerophospholipids and their charges once glycerophospholipids
serine (PS)- (-)
ethanolamine (PE)- 0, zwitterion
choline (PC) - 0, zwitterion
glycerol (Cardiolipin) - (-)
inositol (PI)- (-)
- alcohol head group determines glycerophospholipid charge