Lecture 1 - Amino acids Flashcards
Proteins are polymers of
amino acids
A protein’s amino acid sequence is known as its
primary structure
The primary structure determines the amino acids
3-D structure (conformation)
A protein’s structure determines the _________ of that protein.
function
Amino acids join via
peptide bonds
The ________ of amino acids account for the large variety in protein function.
functional groups
Amino acids contain a central _______ _______ atom (except proline).
tetrahedral carbon
For 19 of the 20 amino acids, the alpha-amino group is
primary
The alpha-carbon is a stereorcenter for every amino acid except
glycine
Which amino acids predominate in nature, L or R?
L
Five groups of amino acid side chains
- Non-polar aliphatic
- Aromatic
- Polar uncharged
- Positively charged
- Negatively charged
Aliphatic amino acids (7)
Glycine
Alanine
Valine
Leucine
Isoleucine
Proline
Methionine
Aromatic amino acids (3)
Phenylalanine
Tyrosine
Tryptophan
Polar, uncharged amino acids (5)
Serine
Threonine
Cysteine
Glutamine
Asparagine
Positively charged amino acids (3)
Lysine
Arginine
Histidine
Negatively charged amino acids
Aspartate
Glutamate
Cysteine residues react with each other to form
disulfide bonds
Cytoplasm is a reducing environment, preventing the formation of
disulfide bonds
Which amino acid can bind and release protons near physiological pH?
Histidine
Amino acids are weak ________ acids
polyprotic
The degree of dissociation in amino acids depends on the pH of the
medium it is in
Alpha carboxyl group pKa
2
Alpha amino group pKa
9
The isoelectric point, pI, is
the pH of an amino acid at which the molecule has an average net charge of zero.
For simple amino acids, the pI is
the average of the pKa’s of the carboxyl and ammonium groups.
For amino acids with additional acidic or basic groups, the pI is
the average of the pKa’s of the two most similar acids.
pKa tells us how acidic a
hydrogen atom in a molecule is
pH tells us how acidic a
solution is
At physiological pH, the _______ group is completely dissociated.
alpha carboxyl
