BioChem CH11/12 E2

what are lipids and 5 classes

-defined as molecules that are not soluble in water
1,Free fatty acids: a common fuel
2,Tricylglycerols:storage form of fatty acids
3,Phospholipids:membrane lipids
4,Glycolipids:membrane lipids composed in part of carbohydrates
5,steroids:polycyclic hydrocarbons with a variety of functions

what are fatty acids

-chains of hydrogen-bearing carbon atoms that have carboxylic acid at one end and a methyl group at the other end
-may be saturated or unsaturated

what are carbons 2/3 called on fatty acids; and what is methyl carbon called

2/3: alpha and beta carbons
methyl: omega

what form are fatty acids referred to in

their carboxylate form

what configuartion are fatty acid double bonds typically in

cis bonds
-in polyunsaturated fatty acids, double bonds are separated by at least 1 methylene group

how is melting point in fatty acids; what are the properties of fatty acids dependent on

-shorter chain=lower melting point
-more cis bonds (double bonds)= lower melting point
-dependent on chain length and degree of unsaturation

what factors determine the melting point of fatty acids

-chain length
-# of cis double bonds

why are cis cunsaturated bonds essential for our diets

bc humans cant synthesize them
-fatty acids are precursors to variety of hormones and appear to offer some protection from coronary heart disease

how are fatty acids storeed

-as tricylglycerols in which 3 fatty acids are esterified to one molecule of glycerol

what are the 3 common types of membrane lipids

-phospholipids
-glycolipids
-cholesterol

what 4 components are phospholipids composed on

-fatty acids (2 or more), a platform, a phosphate, and an alcohol
-2 common platforms are glycerol/sphingosine
-major phospholipids are derived from phosphatidate

what are phospholipids with glycerol platform/sphingosine called

-glycerol: phosphoglycerides or phosphoglycerols
-sphingosine: sphingolipids (common in myelin sheath of nerve cells)

what are glycolipids

-carbohydrate-containing lipids-carbohydrate components are on the extracellular surface of the cell membrane (play role in cell-to-cell interactions)
-cerebrosides are the simplest glycolipids

what are steroids

-lipids that have a variety of roles
-built on tetracyclic platform
-cholesterol is the most common steroid (maintains membrane fluidity)

what are characteristics of membranes

-sheetlike structures
-composed of lipids and proteins
-small amphipathic molecules that form closed bimolecular sheets (prevent movement of polar/charged molecules)
-serve to mitigate the impermeability of membranes and allow movement of molecules
-are noncovalent assemblies
-are asymmetric outer is always different from inside
-are fluid structures
- are electrically polarized (inside is negative)

what do phospholipids and glycolipids form

lipid bilayers in aqueous solutions
-powered by hydrophobic effect

what are liposomes and how are they useful

-they are aqueous compartments enclosed by a lipid membrane
-useful as drug-delivery systems (drugs are more targeted than are systemic drugs= less of body exposed to toxic drugs

what are lipid bilayers impermeable to

-ions and most polar molecules

what is hydrophobicity

-ability of small molecules to cross a membrane
-ions cannot cross membranes bc of the energy cost of shedding their associated water mmolecules

what does membrane processes depend on? and what is melting temperature

-the fluidity of the membrane
-temp at which a membrane transitions from being highly ordered to very fluid (dependent on length of fatty acids)
-cholesterol helps to maintain proper membrane fluidity

what do membrane proteins allow transport of

-molecules and infro across the membrane

how do proteins associate with lipid bilayer

-integral membrane: proteins are embedded in the hydrocarbon core of membrane
-peripheral membrane: proteins bound to polar head groups or exposed to surfaces of integral membrane proteins
-some are associated by attachment to a hydrophobic moiety that is inserted into the membrane

what are 2 strcutural features of integral membrane proteins

-membrane spanning alpha helices
-beta strands form a pore in membrnae or by embedding part of the protein into the membrane

how did they prove membrane is fluid (EXAM)

-fluorescence recovery after photobleaching (FRAP) showed measurement of lateral mobility of membrane components
-membrane component is attached to fluorescent molecules
-on very small portion of membrane, dye is destroyed by high-intensity light (bleaching)
-mobility is a function of how rapidly the bleached area recovers fluorescence
-lateral diffusion of proteins depends on whether they are attached to other cellular or extracellular components

what are the 2 types of diffusions of lipids

-they rapidly diffuses laterally in membranes
-very slow with transverse or flip-flopping diffusion (very rare without the assistance of enzymes); prohibition accounts for stability of membrane asymmetry

when will a small molecule spontaneously cross a membrane

-if the concentration of molecule is higher on one side than the other
-molecule is lipophilic or soluable in nonpolar solutions

how can polar molecules diffuse across a membrane; what are the types of transport

-only with assistance of a protein called a channel
-this movement is called facilitated diffusion or passive transport
-active transport is movement against concentration gradient and requires a source of energy

what is the Na+-K+ ATPase pump

-uses energy of ATP hydrolysis to simutaneously pump 3 NA+ ions out of the cell and 2 K+ ions into the cell against their concentration gradient

what are secondary transporters

-use one concentration gradient to power the formation of another

voltage vs ligand activaed channels

-voltage: channels acitvated byb changes in the voltage across a membrane
-ligand: cannels activated by binding specific molecules to the channels