Amino acids, peptides and proteins

what property of amino acids means that their charge can change at different pH's?

amphoteric - can accept or donate a proton (act as an acid or base)

what is the isoelectric point of amino acids?

between pH 6.5 and 7.5 - both amino and carboxyl groups are charged

how many different R groups are there in naturally occurring amino acids and how do they vary?

20

shape, size, hydrogen bonding capacity, hydrophobic character, chemical reactivity

give an example of the structure you would find on a non-polar, neutral amino acid

hydrophobic side chain - either aliphatic or aromatic

(no charge or electronegative atoms to form hydrogen bonds, not soluble in water)

describe the properties of a polar, neutral amino acid

partial charges - can form hydrogen bonds

soluble in water

describe the properties of charged amino acids

charged side chains - can form hydrogen and ionic bonds

very soluble in water

what makes amino acids chiral?

the alpha carbon acts as a chiral centre bonded to 4 distinct groups (apart from glycine)

what does pI mean?

isoelectric point - point which it holds a net charge of zero

how do you calculate pI?

neutral: take the average of the pKa’s (one for the deprotonation of the amino group and one for the deprotonation of the carboxyl group)

acidic: ½ (pKa of carboxyl + side chain pKa)

basic: ½ (pKa of amine + side chain pKa)

state 3 ways by which amino acids can be separated

electrophoresis, polarity, exchange chromatography

between which two atoms on amino acids does a peptide bond form between?

C in C=O of one amino acid, N in N-H of the other

how are peptide bonds resonance stabilised?

electrons are shared unequally, greater electron density on the oxygen than on N

orbital overlap gives partial double bond character to the amide bond