lecture 4 - amino acids & peptides Flashcards
What is the basic structure of an amino acid?
Central alpha carbon, R side chain, amino group, carboxylic group
Are amino acids in nature L or D stereoisomers?
Almost always L
Which amino acid does not have a chiral carbon, and is therefore not a stereoisomer?
Glycine
As the pH of a solution increases, are amino acids protonated or deprotonated?
deprotonated
What are the 3 key classifications of amino acids?
Non-polar, polar (uncharged), polar (charged)
What are the 2 amino acids that have acidic side chains?
Aspartame, glutamate
What are the 3 amino acids that have basic side chains?
Lysine, arginine, histidine
How would an amino acid mutation in a protein be described using single letter codes?
3 letter code for mutation - 1st letter=original aa, 2nd letter=location of mutant on protein chain, 3rd letter=new residue
What reaction type is involved in the formation of a disulphide bond?
Oxidation reaction
What is the double bond character of the peptide bond?
40% double bond character
Is the peptide bond planar or non-planar?
Planar
What is the value of the rotational barrier of the peptide bond?
80KJ/mol
What is the ‘rotational barrier’ of a bond?
The difference in energy between the most stable and least stable configurations of rotation around a bond.
Are peptide bonds usually cis or trans?
Trans
Why do peptide bonds have dipoles?
The double bond resonance form produces a dipole
What is the name for an amino acid when it is in a polypeptide chain?
An amino acid residue
Are amino acids typically charged or uncharged in solution?
Usually exist as zwitterions in neutral solution so have a net neutral charge, but the side amino and carboxyl groups are equally and oppositely charged.
What is the nature of an amino acid at its pI?
Has no net charge
What is the pI of an amino acid?
The isoelectric point - the pH at which an amino acid has no net charge
Which amino acid is involved in disulfide bridge formation?
Cysteine
What is phosphorylation, in terms of amino acid modification?
The covalent addition of a phosphate group to a residue
What is hydroxylation, in terms of amino acid modification?
The addition of a hydroxyl (OH) group to an amino acid
What is carboxylation, in terms of amino acid modification?
The addition of a carboxylate group to an amino acid residue
What is metal binding, in terms of amino acid modification?
The binding of a metal ion to a peptide
What is iodination, in terms of amino acid modification?
The addition of an iodine atom to an amino acid residue/protein
What is glycosylation, in terms of amino acid modification?
The addition of a sugar/carbohydrate molecule to an amino acid in a protein chain.
