* 4 Flashcards
4 ways that carbon skeletons can vary
length, branching, double bond positions, presence of rings
fat
- molecules w/ long hydrocarbon tails attached to a nonhydrocarbon component.
- constructed from 2 kinds of smaller molecules: glycerol and fatty acids
- triacylglycerol (or triglyceride): 3 fatty acid molecules are each joined to glycerol by an ester linkage
enantiomers
- mirror isomers
- differ in shape b/c of an asymmetric carbon, one that is attached to 4 diff atoms / groups of atoms
- only 1 isomer is biologically active b/c only that from can bind to specific molecules in an organism
functional groups
chemical groups that affect molecular function by being directly involved in chemical reactions. each functional group participates in chem rxns in a characteristic way from 1 orgnanic molecule to another
disaccharide
- 2 monosaccharides joined by a glycosidic linkage, a covalent bond formed btwn 2 monosaccharides by a dehydration rxn.
storage polysaccharides: plants
- plants store STARCH, a polymer of glucose monomers, as granules within cellular structures known as plastids, which include chloroplasts. most of the glucose monomers are joined by 1-4 linkages.
- the simplest form of starch, AMYLOSE, is unbranched. AMYLOPECTIN, a more complex form, is branched w/ 1-6 linkages at the branch points
storage polysaccharides: animals
- animals store GLYCOGEN, a polymer of glucose that is like amylopectin but more extensively branched. stored as dense clusters of granules within liver and muscle cells
- hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases
- glycogen can’t sustain an animal for long – depleted in a day if not replenished
cellulose
- major component of cell walls.
- polymer of glucose.
- animals can’t digest cellulose; it’s eliminated w/ feces. along the way, cellulose abrades the wall of the digestive tract and stimulates the lining to secrete mucus, which aids in the smooth passage of food thru the tract. “insoluble fiber” (but microorganisms living in cows and termites’ gut can)
starch vs cellulose
- shape: starch molecules are helical; cellulose molecules are straight, never branched
- starch: gluclose monomers in alpha configuration
- cellulose: beta (each monomer is “upside down” w/ respect to its neighbors)
microfibrils
- some hydroxyl groups on the glucose monomers of cellulose are free to hydrogen-bond w/ the hydroxyls of other cellulose molecules lying parallel to it. parallel cellulose molecules held together in this way are grouped into units called microfibrils.
- cable-like; strong building material for plants
- 80 cellulose molecules long
chitin
- the carb used by arthropods (insects, spiders, crustaceans, etc) to build their exoskeletons
- pure chitin is leathery and flexible, but becomes hardened when encrusted w/ calcium carbonate, a salt
- found in many fungi, which use it as the building material of their cell walls
- beta linkages, but the glucose monomer has a nitrogen-containing appendage
glycerol
an alcohol. each of its 3 carbons bears a hydroxyl group.
why do fats separate from water?
nonpolar C-H bonds in the hydrocarbon chains of fatty acids make fats hydrophobic. the water molecules hydrogen-bond to one another and exclude the fats.
ester linkage
a bond btwn a hydroxyl and a carboxyl group.
fatty acid
- has a long carbon skeleton, usually 16 or 18
- the carbon at 1 end of the skeleton is part of a carboxyl group, which gives it the name ‘acid’
saturated fatty acid
- there are no double bonds btwn carbon atoms composing a chain. as many H atoms as possible are bonded to the C skeleton. (saturated w/ hydrogen)
- no double bonds –> flexibility allows the fat molecules to pack together tightly
unsaturated fatty acid
- 1 or more double bonds btwn the carbon atoms composing a chain, w/ 1 fewer H atom on each double-bonded C.
- nearly all double bonds in naturally occurring fatty acids are cis double bonds, which cause a kink in the hydrocarbon chain wherever they occur.
saturated vs unsaturated fats
- most animal fats are saturated. ex: lard and butter. solid at room temp
- most plant and fish fats are unsaturated. liquid at room temp.
why are unsaturated fats liquid at room temp?
the kinks where the cis double bonds are located prevent the molecules from packing together closely enough to solidify at room temp.
trans fat
the process of hydrogenating vegetable oils produces not only saturated fats but also unsaturated fats w/ trans double bonds
atherosclerosis
- cardiovascular disease
- deposits called plaques develop w/in the walls of blood vessels, causing inward bulges that impede blood flow and reduce the resilience of the vessels
omega-3 fatty acids
- required for normal growth in children
- protect against cardiovascular disease in adults
- so named b/c they have a double bond at the 3rd carbon-carbon bond from the end of the hydrocarbon chain