Intro to Amino Acids Flashcards
Which four groups are attached to the central carbon (α) of an amino acid?
- amino group (-NH2)
- carboxylic acid group (-COOH)
- hydrogen atom
- R group (side chain which varies in every single amino acid)

Which amino acid is the smallest?
Glycine
All amino acids are chiral (or has a stereogenic center), with the exception of?
Glycine
The α-carbon of most amino acids is chiral and optically active. Glycine is achiral because its R group is a hydrogen atom and it is therefore optically inactive.
Which four amino acids have alkyl side chains? (containing one to four carbons)
- alanine
- valine
- leucine
- isoleucine
Which amino acid has an unbranched alkyl side chain?
Alanine
(Alanine only has a methyl side chain and is therefore unbranched.)
Which three amino acids have uncharged aromatic side chains?
- phenylalanine (F)
- tryptophan (W)
- tyrosine (Y) (polar)
Which two amino acids have R groups that are acidic and negatively charged?
- glutamate (E)
- aspartate (D)
Which three amino acids have R groups that are basic and positively charged?
- arginine (R)
- histidine (H)
- lysine (K)
Which two amino acids have sulfur in their R groups?
- methionine
- cysteine
Which amino acid creates kinks in α-helices and creates turns in β-pleated sheets?
Proline
Any amino acid with -OH in its R group can undergo which two processes?
- reversible bonding
- phosphorylation
Which three amino acids can undergo reversible bonding and phosphorylation, due to the presence of -OH in their R groups?
- serine (S)
- threonine (T)
- tyrosine (Y)
Which two amino acids have amide groups in their side chains that can be removed via transamination (or deamidation)?
- asparagine
- glutamine
Which amino acid is the only one with two rings?
Tryptophan
Which amino acid can serve as both an acid AND a base?
Histidine
(Because its pKa is close to physiological pH.)
Which amino acid is involved in metabolism?
Alanine
Which amino acid has a pKa of 6?
Histidine
Because histidine has a pKa of 6, it has a 50% chance of being protonated (positively charged) OR deprotonated (neutral) at physiological pH.
Which amino acid is involved in the formation of disulfide bridges?
Cysteine

(has a thiol (-SH) group in its side chain)
What is the average molecular weight (MW) of ONE amino acid residue in a protein?
110 Da
(110 g/mole)
Which two amino acids are constitutional isomers?
- leucine
- isoleucine
Amino acids can occur in L and D configurations. Which configuration do eukaryotic organisms prefer?
L-configuration
(Only L-amino acids are manufactured in eukaryotic cells and incorporated into proteins.)
Which three amino acids are an important source of energy in skeletal muscles and signals cells to synthesize proteins?
- leucine
- isoleucine
- valine
All three of these amino acids are branched.
Which three amino acids can act as nucleophiles during enzymatic catalysis?
- serine
- threonine
- cysteine
Which three amino acids function in absorbing UV light?
- tryptophan (280 nm)
- tyrosine (274 nm)
- phenylalanine (257 nm)
All amino acids have an (S) absolute configuration, with the exception of?
Cysteine
Which amino acid allows a protein to be flexible?
Glycine
(Glycine is the smallest amino acid and only has a hydrogen atom as its side chain.)
Which two amino acids are used in in alpha helix and beta pleated sheet turns?
- glycine
- proline
What is the one letter and three letter abbreviation for the amino acid tryptophan?
Tryptophan: (W) Trp
What is the one letter and three letter abbreviation for the amino acid lysine?
Lysine: (K) Lys
What is the one letter and three letter abbreviation for the amino acid threonine?
Threonine: (T) Thr
What is the one letter and three letter abbreviation for the amino acid tyrosine?
Tyrosine: (Y) Tyr
What is the one letter and three letter abbreviation for the amino acid glutamine?
Glutamine: (Q) Gln
What is the one letter and three letter abbreviation for the amino acid glycine?
Glycine: (G) Gly
What is the one letter and three letter abbreviation for the amino acid leucine?
Leucine: (L) Leu
What is the one letter and three letter abbreviation for the amino acid asparagine?
Asparagine: (N) Asn