Quiz 2 Flashcards
List the amino acids with non-polar, aliphatic R groups
List the amino acids with aromatic R groups
What two amino acids absorb light around 280nm?
Tryptophan and Tyrosine
List the amino acids with polar, uncharged R groups
List the amino acids with positively charged R groups
The side-chain of basic amino acids can take up an extra proton to become positively charged. Histidine is only weakly basic at neutral pH (pH 7), as only some of the side-chains have taken up a proton (about 10%).
List the amino acids with negatively charged side groups
The side-chain of acidic amino acids can give up a proton (H+) to become negatively charged.
What is the distinction between peptides and proteins proper?
Amino acid polymers < 10,000 Da in molecular weight (MW) are considered peptides; those above 10,000 Da are proteins.
Polymers composed of two amino acids are called
dipeptides
Polymers composed of three amino acids are called?
tripeptides
Polymers composed of more than three amino acids are called?
polypeptides
How do amino acids polymerise?
Through condensation (loss of H2O)
What is the accepted pKa for C-termini
2.2
What is the accepted pKa for N-termini
9.5
Which amino acids act as the primary acids and bases?
Those with polar, charged side chains:
Asp pKa ~3.7
Glu pKa ~4.2
His pKa ~6.0
Lys pKa ~10.5
Arg pKa ~12.5
Additionally, Cys (pKa ~8.4) and Tyr (pKa ~10.5) are both weakly acidic
What effect does the local environment have on the pKa of an amino acid?
Hydrophobic environments may favor non-charged residues (e.g. protonated carboxylic acid groups or unprotonated basic groups)
Hydrophilic conditions/electrostatic interactions may favor charged residues (e.g. unprotonated carboxylic acid groups or protonated basic groups)
Additionally, stabilisation by nearby residues may affect acidity and basicity