BIOC3021 #5 - Amino Acids

Components of an Amino Acid

• An alpha-carbon covalently linked to:

  • Amino Group (-NH2)

  • Carboxyl Group (-COOH)

  • Variable Side Chain (R-group)

  • Hydrogen (-H)

Non-polar (hydrophobic) Amino Acids:

• Alanine (Ala, A)

• Valine (Val, V)

• Leucine (Leu, L)

• Isoleucine (Ile, I)

• Phenylalanine (Phe, F)

• Tryptophan (Trp, W)

• Methionine (Met, M)

• Proline (Pro, P)

Alanine (Ala, A)

Akyl chain R-group

Valine (Val, V)

Akyl chain R-group

Leucine (Leu, L)

Akyl chain R-group

Isoleucine (Ile, I)

Akyl chain R-group

Phenylalanine (Phe, F)

Aromatic ring

Tryptophan (Trp, W)

Aromatic ring

Methionine (Met, M)

Sulfur-containing

Proline (Pro, P)

Unusual cyclic structure

Polar (hydrophilic) Amino Acids

• Glycine (Gly, G)

• Serine (Ser, S)

• Threonine (Thr, T)

• Tyrosine (Tyr, Y)

• Asparagine (Asn, N)

• Glutamine (Gln, Q)

• Cysteine (Cys, C)

• Histidine (His, H)

Glycine (Gly, G)

Simplest R group (H) ➡ Cannot form H bonds

Serine (Ser, S)

Hydroxyl in R-group

Threonine (Thr, T)

Hydroxyl in R-group

Tryosine (Tyr, Y)

Hydroxyl in R-group

Asparagine (Asn, N)

Amide in R-group

Glutamine (Gln, Q)

Amine in R-group

Cysteine (Cys, C)

Sulfur-containing ➡ ONLY amino acid that can form a disulfide bond

Histidine (His, H)

Acidic Amino Acids Definition

Amino acids that are negatively charged at pH = ~7.0

Acidic Amino Acids

• Aspartic Acid (Asp, D)

• Glutamic Acid (Glu, E)

Aspartic Acid (Asp, D)

Carboxyl in R-group

Glutamatic Acid (Glu, E)

Carboxyl in R-group

Basic Amino Acids Definition

Amino acids that are positively charged at pH = ~7.0

Basic Amino Acids

• Lysine (Lys, K)

• Arginine (Arg, R)

Lysine (Lys, K)

Positively-charged nitrogen-containing group

Argenine (Arg, R)

Positively-charged nitrogen-containing group

Uncommon, Chemically-Modified Amino Acids

• 5-Hydroxylysine: modified lysine

• N-acetyllysine: modified lysine

• Thyroxine: 2 modified tyrosine

• Carboxyglutamic Acid: modified glutamic acid

5-Hydroxylysine

• Modified lysine

  • Found in collagen

N-acetyllysine

• Modified lysine

  • Found in histone proteins

Thyroxine

• 2 modified tyrosine

  • The thyroid hormone

Carboxyglutamic Acid

• Modified glutamic acid

  • Involved in blood clotting

A positive (low pH) Amino Acid contains:

-NH3+

-COOH

A neutral (pH = ~7.0) Zwitterionic Amino Acid contains:

-NH3+

-COO-

A negative (high pH) Amino Acid contains:

-NH2

-COO-

Reactions of Amino Acids

1. Formation of a peptide bond (condensation/dehydration reaction)

2. Formation of a disulfide bridge

The formation of a peptide bond (condensation/dehydration reaction) is…

Formed by the reaction of the carboxyl group (-COO-) of one amino acid and the amino group (-NH3+) of another ➡ CO - NH

Enantiomer

A pair of molecules that are non-superimposable mirror images

L- Amino Acid

• An amino acid with its amino group (-NH2) on its left

  • All amino acids found in proteins are L-amino acids

D- Amino Acid

An amino acid with its amino group (-NH2) on its right

Separation of Amino Acids by Ion Exchange Chromatography

In a mixture, increasing Na+ concentrations DISPLACE the amino acids from LEAST positively charged to MOST positively charged