amino acids, polymers and proteins Flashcards
general formula of an amino acid
NH2–CHR–COOH
what is a zwitterion
ion with both a positive and negative charge that’s overall charge cancels out.
define isoelectric point
the pH at which a zwitterion forms in solution
how does an amino acid form a zwitterion
the H from the COOH of one molecule will protonate the NH2 group of another molecule
what groups does an amino acid zwitterion contain
NH3+ and COO-
what are three physical properties of amino acids
white solids
high melting point (around 300)
water soluble
at what pH can an amino acid act as an acid and why
low pH
COOH has a proton to donate
at what pH can an amino acid act as a base and why
high pH
N has a lone pair of electrons which can accept a proton
what is amphoteric behaviour
when a substance can act as both an acid and a base, depending on the chemical environment
which is the only amino acid that is not optically active
glycine
why is glycine the only amino acid that is not optically active
it does not have a chiral carbon as the R group is a Hydrogen
what is the bond between amino acids in a peptide/polypeptide called
an amide link
what type of polymer are polypeptides
condensation polymers
two steps to hydrolyse peptide bonds
1 heat under reflux with HCl for up to 24hrs
2 followed by addition of water
what does a condensation reaction produce
polymer and a small molecule eg H20 or HCl
what are polyesters formed from
a dicarboxylic acid and a diol
or a diacyl chloride and a diol
what are polyamides formed from
a dicarboxylic acid and a diamine
what is the ester functional group formed in a polyester
O=C-O
what is the amide group in a polyamide
O=C-NH
what is the glycine R group
H-
what is the alanine R group
CH3-
what is the valine R group
(CH3)2CH-
what is the cysteine R group
HS-CH2-
what is the phenylalanine R group
C6H5-CH2-
