(NOT FINISHED) 05 - amino acids and peptides

what four groups are attached to the α-carbon of most amino acids?

a carboxyl group, an amino group, a hydrogen atom, and an R group

what is unique about glycine compared to other amino acids?

it has a second R group instead of a hydrogen atom attached to the alpha carbon

what determines the identity and properties of an amino acid?

the R group attached to the alpha carbon

what is the chiral center of the amino acid?

the alpha carbon

why can the α-carbon of amino acids have two unique spatial arrangements?

because it has a tetrahedral shape of bonding orbitals allowing the four different groups to occupy two distinct spatial arrangements

how many possible stereoisomers do amino acids have?

2

what causes amino acids to have stereoisomers?

the alpha carbon is chiral which allows for different spacial arrangements

what is another name for a chiral center?

asymmetric carbon

what defines a chiral (asymmetric) carbon?

an atom with substituents arranged so that the molecule is not superimposable on its mirror image

what are enantiomers?

the two possible stereoisomers

what defines an L-amino acid?

the α-amino group is on the left

what defines a D-amino acid?

the α-amino group is on the right

which amino acid’s R groups are hydrophilic because they can form hydrogen bonds with water? what makes these molecules polar?

serine, threonine, cysteine, asparagine, glutamine; the hydroxyl, amide, and sulfhydryl (forms disulfide bonds) groups

which amino acids have an R group with a significant positive charge at pH 7.0?

lysine, arginine, and histidine

what functional group does histidine have that affects its charge?

an imidazole group.

at pH 7.0, what are the possible charges of histidine?

it may be positively charged (protonated) or uncharged.

why can histidine be either protonated or uncharged at physiological pH?

because the pKa of its imidazole side chain is close to 7, allowing it to exist in both forms.

which amino acids have an R group with a new negative charge at pH 7?

aspartate and glutamate