Amino Acids Flashcards
What are amino acids and how do they build polypeptide chains?
Amino acids are monomers or proteins. Amino acids are joined by peptide bonds during condensation reactions to form polypeptide chains.
What is common structure of amino acids?
- Carboxylic acid -COOH
- Amino group - NH2
- H atom
- R group (unique for every amino acid so determines identity)
Polypeptide chain has directionality. What does this mean?
Two ends of chain are chemically distinct. N-terminus (amino end) has a free amino group. C-terminus (carboxyl end) has a free carboxyl group.
What determines chemical behaviour of amino acid?
The R group
Lysine (at physiological pH)
Electrically charged: side chain is positively charged. Considered basic amino acid
Acidic Amino Acids: side chains are negatively charged
Aspartic acid (Asp) Glutamic acid (Glu)
Basic Amino Acids: side chains are positively charged
Lysine (Lys)
Arginine (Arg)
Histidine (His)
Non-Polar (Hydrophobic) Amino Acids
Glycine (Gly) Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) Methionine (Met) Tryptophan (Trp) Phenylalanine (Phe) Proline (Pro)
Polar (Hydrophilic) Amino Acids
Serine (Ser) Threonine (The) Cysteine (Lys) Tyrosine (Tyr) Asparagine (Asn) Glutamine (Gln)
Glycine at physiological pH?
Non-polar (hydrophobic)
Histidine at physiological pH?
Side chain is positively charged: basic amino acid.
ALTHOUGH, at pH 7 side chain is mainly uncharged
Arginine at physiological pH?
Side chain is positively charged: basic amino acid
Which is the only amino acid that isn’t chiral / doesn’t posses optical activity?
Glycine
What do optical isomers do?
Rotate plane-polarised light in opposite directions
What is physiological pH?
7.2-7.4
At physiological pH, what is the amino group and carboxyl group typically like?
Amino group typically protonated (has positive charge)
Carboxyl group typically deprotonated (has negative charge)
What is pKa?
The pH at which a group is 50% ionised
What is the pKa for carboxylic acid groups?
Roughly 1.8 – 2.5; almost always negatively charged
What is the pKa for amino groups?
Roughly 9-10; almost always positively charged
What is the pKa for histidine?
Roughly 6.0
If a pH is below pKa, what is seen?
Group will have H attached
