Lipids Flashcards
features of lipids
macromolecules - high molecular weight
important in cellular structures (membranes)
Hydrophobic (soluble in nonpolar solvents such as chloroform or other)
have relatively few polar groups, but some are amphipathic, having polar and nonpolar regions
Diverse functions
Functions of lipids
energy storage
membrane structure
signaling (steroid hormones)
electron transport (coenzyme Q)
pigments
antioxidants (vitamin E)
The main classes of lipids
Fatty acids
Triacylglycerols
Phospholipids
Glycolipids
Steroids
Terpenes
Saturated fatty acids
each carbon atom in the chain is bonded to the maximum number of hydrogens, have long straight chains that pack together well CnH2nO2
Fatty acids without double bonds
Unsaturated fatty acids
have one or more double bonds, so they have bends (angle) in the chains and are less tightly packed
head and tail of fatty acids
polar carboxyl group - head
non-polar hydrocarbon chain - tail
Polyunsaturated fatty acids
have more than one double bond
linoleate - 18-carbon unsaturated fatty acids
Triacylglycerols
glycerol (3-carbon alcohol with a hydroxyl group on each carbon) + 3 fatty acids (by ester bonds formed by the removal of water)
The main function of triacylglycerols
energy storage
insulation against low temperatures
the most abundant lipids in the membrane?
Phospholipids
What do Phospholipids include?
phosphoglycerides or sphingolipids, depending on their chemistry
common alcohol groups (small hydrophilic alcohol linked to P by ester bond) of phosphoglycerides?
serine, ethanolamine, choline, or inositol, which contribute to the polar nature of the phospholipid head group
basic component of phosphoglycerids
phosphatic acid (two fatty acids and a phosphate group attached to glycerol)
Phosphate is charged under physiological pH
What are sphingolipids based on?
sphingosine - has a long hydrocarbon chain with a single site of unsaturation near the polar end
How a molecule ceramide is formed?
Sphingosine can form an amide bond to a long-chain fatty acid (up to 34 carbons), resulting in a molecule called a ceramide
different polar groups attached to the hydroxyl group of the ceramide -> whole family of sphingolipids
diversity of sphingolipids
sphingomyelins
accumulation of sphingomyelin leads to Niemann-Pick disease – mental retardation, early death (due to lack of sphingomyelinase)
a long, unbranched hydrocarbon chain with a carboxyl group at one end -> amphipatic
fatty acid
function of phospholipids
due to amphipatic nature -> key component of bilayer structure in membrane
Where sphingolipids can be found?
in the outer leaflet of the plasma membrane bilayer, often in lipid rafts (in the outer monolayer of animall cells have elevated levels of cholesterol an sphingolipids; less fluid than the rest of the membrane)
roles of lipid rafts
transporting nutrients and ions across membranes
binding activated immune system cells to their mirobial targets
transporting cholera toxin into intestinal cells
how glycolipids are formed?
by the addition of carbohydrates to lipids
derivatives of sphingosine or glycerol
the most common glycolipids that are prominent in brain and nerve cells
cerebrosides
gangliosides
what are cerebrosides?
neutral glycolipids
each molecule has a sugar as its head group
what are gangliosides?
has an oligosaccharide head group with 1 or more negatively charged sialic acid residues
what are steroids?
what is their polarity?
derivatives of a 4-ringed hydeocarbon skeleton, which distinguishes them from other lipids
relatively nonpolar->hydrophobic
how do steroids differ from one another?
in the positions of double bonds and functional groups
Cholesterol - most common steroid
structure?
contains a rigid ring structure + single polar hydroxyl group + short nonpolar hydrocarbon chain
How does cholesterol orient itself?
in the bilayer, it orients with hydroxyl grouo close to the polar head group of adjacent phospholipid molecule
2 kinds of steroid hormones
glucocorticoids
mineralocorticoids
What are the glucocorticoids?
e.g. cortisol
family of hormones promoting synthesis of glucose and suppress inflammation
What are mineralocorticoids?
e.g. aldosterone
regulate ion balance by promoting reabsorption os Na, Cl, bicarbonate ions by kidney
From what terpenes are synthesized?
5-carbon compound isoprene (isoprenoids)
Isoprene and its derivatives are joined to
produce substances such as vitamin A and cartenoid pigments
What are isoprene-based compounds, dolichols, involved in?
activating sugar compounds (during assembly of bacterial cell wall, addition of polysaccharide units to certain proteins and lipids)
What are other isoprene-based compounds?
electron carriers such as coenzyme Q (ubiquinone) and plastoquinone
polyisoprenoids (polymers of isoprene) are found in cell walls of the Archae
What is osmosis?
movement of water: low solute C -> high solute C through water diffusion
What facilitate water flow?
aquaporins (water channels)
What is tonicity?
relative concentrations of solutes in 2 solutions
determines movement of water into ot out of cells
Hypotonic solution
low solute C/high water C
red blood cells exposed to it will swell and burst
Hypertonic solution
high solute C/low water C
red blood cells exposed to it will shrink
Isotonic solution
the same osmotic pressure as referenced solution
for human blood=0.9% NaCl
2 driving forces for passive transport
concentration gradient
electrical gradient (for ions)
What is passive membrane transport?
passage of hydrophobic and small polar molecules via diffusion (osmosis)
