lecture eleven - lipids and membranes Flashcards
lipids
soluble in non-polar solvents, highly hydrophobic, most reduced class of biological compounds, release energy upon oxidation
sterols
hormones, perhydrocyclopentanophenanthrene ring structure
NOT aromatic, NOT planar
fatty acids
linear hydrocarbons with one carboxyl group at one end and many methylene groups in the side chain
12-24 C
hydrophobic character increases with chain length
double bonds increases the solubility of the compounds in water and decrease their melting point
triaglycerols
MAJOR STORAGE of lipids
3 fatty acids esterified to glycerol
relatively non-polar, highly reduced (saturated)
phosphoglycerols
membrane components
2 fatty acids, glycerol, phosphate, ionic or polar alcohol
fatty acid at 1 position = saturated
fatty acid at 2 position = unsaturated
phosphatidyl choline is the derivative
sphingolipids
membrane functions
similar in overall structure of phosphoglycerols
polyisoprenoid
vitamin A and beta-carotene
resembles polymers of isoprene but have a very different biochemical origin
energy storage =
triaglycerols
membrane components =
phosphoglycerol
hormones =
sterols
biological detergents =
bile acids
insulating material =
phospholipid and sphingomyelin
vitamins =
polyisoprenoid
highly hydrophobic (non-polar) so can be extracted into non-polar solvents
fatty acids
what characteristics determine the melting point and water solubility of a fatty acid
melting point increases with chain length
double bonds decrease melting points & increase solubility
at temperature below the melting point, they will be solid
above melting point, exhibit fluid character
functions of fatty acids
major energy storage material
critical part of biological membranes
lipid derivatives function as hormones
other derivatives are biological detergents
triglycerols consist of
3 fatty acids esterified to glycerol
phosphatidic acid has
2 fatty acids esterified to glycerol
saturated fatty acid
do NOT have double bonds, linear zig-zag structure, are solid at room temperature
monounsaturated fatty acid
1 double bond, 1 unit of unsaturation
polyunsaturated fatty acid
2+ double bonds
how do double bonds change the structure of a fatty acid from a linear to bent form?
unsaturated fatty acids tend to be in the “cis” configuration where the chain continues at a new angle, resulting in a bend
mono and polyunsaturated fatty acids contribute to
the liquid nature of membranes
how are trans isomers formed during the chemical hydrogenation of unsaturated fatty acids?
hydrogenation increases lipid solubility, double bonds are converted to single bonds
how do trans fatty acids influence human health?
trans fatty acids have double bond in trans configuration and this has been shown to increase the risk of CAD
major storage of fatty acid in humans
triacylglycerols
how are triacylglycerols broken down in the intestine? where are they reassembled? where are they taken?
broken down in the lumen of the intestine
component fatty acids and monoacylglycerols
are taken up into the intestinal epithelial cells - where triacylglycerols are reassembled then released in the lymph, and are transported through chylomicrons to adipose cells
where are triacylglycerols stored?
in adipocytes, until there is a need for energy
phosphoglycerols
related to triacylglycerols, but the third carbon is connected to a phosphate residue
fatty acid at the first carbon tends to be saturated
fatty acid at the second carbon tends to be unsaturated
hydroxyl group at the third carbon is connected to the phosphate
major physiological function of phosphoglycerols
serve as membrane components; important to contain unsaturated fatty acids – the fatty acids contribute to the fluid mosaic structure of membranes
phosphatidyl choline
lecithin; carries a positive permanent charge, isn’t affected by pH
phosphatidyl ethanolamine
alcohol derivative, amine group is positively charged at physiological pH
phosphatidyl inositol
polyhydroxyl compound, highly polar but uncharged
phosphatidyl serine
has positively charged amine and negatively charged carboxyl
how do sphingomyelin compounds differ from phosphoglycerols?
sphingosine replaces glycerol; provides HC chain and a long chain FA
amide linkage provides a second HC chain
has phosphate and polar alcohol
cerebrosides
sphingolipids that have glucose or galactose instead of phosphate and choline
brain and nervous tissues
gangliosides differ from cerebrosides in that…
the carbohydrate component is more complex and varied
why is it important for the fluid mosaic membrane to contain phospholipids that are rich in unsaturated fatty acids?
unsaturated fatty acids contribute to the fluidity of the membrane and allow proteins to diffuse in a lateral direction, and associate/interact in a functional manner
basic structure of cholesterol
class of sterols with perhydrocyclopentanophenanthrene ring; NOT aromatic, NOT planar
precursor of bile acids and sterol hormones
derived from cholesterol, act as biological detergents
bile salts
bile salts
stored in the gallbladder, released when lipids are metabolized
break lipids up into smaller particles, making triglycerol compounds more accessible to lipase enzymes
common steroid hormones derived from cholesterol
progesterone, testosterone, estradiol
prostaglandins
lipids that are synthesized in complex pathways from arachidonic acid; have hormone-like functions for short time periods
NSAIDs block…
prostaglandins to reduce pain
how and why do phospholipids form vesicle bilayers and what are the characteristics of these bilayers?
interior of bilayers tend to be hydrophobic, vesicles are formed that carry water through the membrane
polar and non-polar regions; water-filled spherical lipid bilayers
vesicle bilayers function as
artificial cells and can transport molecules across mammalian membranes
micelle
no water inside, hydrophobic interior
vesicles
water-filled interior
the key component of fluid mosaic model
polyunsaturated fatty acids in membrane phospholipids
movement of fluid mosaic model protein molecules
fluidity allows them to diffuse laterally, but they do not rotate
features of fluid mosaic model
phospholipid and glycolipid molecules mosaic of non-polar protein molecules that are embedded in the membrane bilayer
bilayer serves as permeability barrier for polar and ionic membrane and as SEMI-fluid solvent for integral membrane protein
protein diffuse in lateral direction in the plane of the membrane, but do not rotate (flip-flop)
components of FMM
phospholipid bilayer
integral proteins (immersed in the non-polar core)
peripheral proteins are found attached to both faces of bilayer
cholesterol immersed in the non-polar interior of the bilayer
glycolipid and glycoprotein on the outer, extracellular face of the membrane
inner leaflet of FMM
tend to have phospholipids with net negative charge
outer leaflet of FMM
phospholipids tend to be neutral
FMM membrane asymmetry is for…
cell homeostasis
how do components of fluid membranes diffuse?
membrane proteins and lipids diffuse laterally in the plane of the membrane; do NOT rotate from one side to another
complex carbohydrates are found where on the membrane
extracellular face, attached to glycoproteins and proteoglycans
why are phospholipids distributed asymmetrically in the membrane and what is the consequence of this distribution?
inner leaflet is rich in phospholipid with net (-) charge
outer leaflet has neutral phospholipids
consequence = different charges
integral membrane proteins (location and removal)
immersed in nonpolar interior of the membrane with high % of nonpolar amino acids
difficult to remove from the membrane, need detergents
peripheral proteins (location and removal)
not immersed in the interior of membrane, attached to outer face by various interactions; can be removed with mild treatments, relatively polar and don’t need stabilizer
in what ways is the protein glycophorin typical of integral membrane proteins?
has a series of hydrophobic amino acids that are immersed in the membrane with alpha-helical conformation
what part of the glycophorin protein are hydrophobic? which is hydrophilic?
single-membrane spanning alpha-helix that is highly hydrophobic
the outside of glycophorin is mostly hydrophilic amino acids and water-soluble, with carbohydrates attached
the inside of glycophorin is hydrophilic amino acids with no carbohydrate attached
what is a hydropathy plot, and what do such plots tell us about membrane proteins such as glycophorin?
measures the occurrence of its hydrophobic, membrane-spanning alpha helix structures
non-polar amino acids exhibit (+) values
used to construct models of membrane proteins
10 amino acids at a time, starting from the terminal end
what types of compounds can pass through a biological membrane using simple diffusion
small, non-polar molecules and gases
ex: O2, CO2, N, urea, ethanol
simple diffusion
no energy or help needed
diffusion from high to low concentration
not saturated, not sensitive to inhibitors
facilitated diffusion
move through a protein tunnel, still with no energy needed
sugars, amino acids, ions, nucleotides, and water diffuse this way
molecular characteristics of the integral membrane protein transport systems
calcium-ATPase transport calcium ions across mammalian membranes
non-polar with lots of non-polar amino acids
active transport system
substrate moves through a tunnel with energy, low to high concentration
primary active transport
directly coupled to ATP hydrolysis, against a concentration gradient,
direct coupling to an energy source
saturable and sensitive to inhibitors
secondary active transport
energized by ion gradients (Na+ or K+)
first established by a primary system, then indirectly coupled to ATP hydrolysis
saturable and can be inhibited
SYMport
part of secondary active transport; couple the downhill flow of one species to energize the uphill flow of another in the SAME direction across the membrane
ANTIport
part of secondary active transport; couple the downhill flow of one species to energize the uphill flow of another in the OPPOSITE direction across the membrane
