MCAT Studies: Amino Acids

Amino Acids

Chart division of amino acids based on properties:

Acidic	Basic	Polar	Nonpolar
Aspartic acid  Glutamic acid	Lysine*  Arginine?  Histidine*	Serine  Cysteine  Tyrosine  Threonine*  Asparagine  Glutamine	Glycine  Alanine  Valine*  Leucine*  Isoleucine*  Phenylalanine*  Tryptophan*  Methionine*  Proline

* Essential amino acids, (Arginine is debated).

PVT TIM HALL - Essential Amino Acids

Aspartic acid, Asp (D)

• Acidic → if deprotonated, (-) charged side chain
• Aspartate = deprotonated aspartic acid

Glutamic acid, Glu (E)

• Acidic → if deprotonated, (-) charged side chain
• Glutamate = deprotonated glutamic acid

Lysine, Lys (K)

• Basic → if protonated, (+) charged side chain
• Cationic @ physiological pH

Arginine, Arg (R)

• Basic → if protonated, (+) charged side chain
• Cationic @ physiological pH

Histidine, His (H)

• Possible Basic → if protonated, (+) charged side chain
• Possible acidic → if deprotonated, (-) charged side chain
• Side chain close to physiological pH → "His goes both ways," Acid/Base

Glycine, Gly (G)

• Nonpolar → hydrophobic
• Aliphatic side chain → Only H atom as side chain

Alanine, Ala (A)

• Nonpolar → hydrophobic
• Aliphatic side chain → Methyl side chain 

Valine, Val (V)

• Nonpolar → hydrophobic
• Aliphatic side chain → Isopropyl side chain
• V similar in shape to isopropyl 

Leucine, Leu (L)

• Nonpolar → hydrophobic
• Aliphatic side chain → isobutyl side chain

Isoleucine, Ile (I)

• Nonpolar → hydrophobic
• Aliphatic side chain → secbutyl side chain
• Not sure why this one was called iso when sec would have been a more appropriate side chain name.

Phenylalanine, Phe (F)

• Nonpolar → hydrophobic
• Aromatic side chain → phenyl
• Easy to remember this one: alanine structure + phenyl group

Tryptophan, Trp (W)

• Nonpolar → hydrophobic
• Aromatic side chain → indole side chain

Methioine, Met (M)

• Nonpolar → hydrophobic
• Sulfur containing amino acid
• Thioether side chain
• Related to the start codon AUG → codes for methionine

Serine, Ser (S)

• Polar → hydrophilic
• Hydroxyl side chain

Cysteine, Cys (C)

• Polar → hydrophilic
• Sulfur containing amino acid
• Thiol side chain

Tyrosine, Tyr (Y)

• Polar → Hydrophilic
• Aromatic side chain → Phenol

Threonine, Thr (T)

• Polar → hydrophilic
• hydroxyl side chain

Asparagine, Asn (N)

• Polar → hydrophilic
• Amide side chain
• Amide derivative of aspartic acid

Glutamine, Gln (Q)

• Polar → hydrophilic
• Amide side chain
• Amide derivative of glutamic acid

Proline, Pro (P)

• Nonpolar → Hydrophobic
• Unique b/c covalently bonded to nonpolar side chain
• Has α-amino group

I will need to really mesh these structures together and test out what works best for memorization.

So far the 4 easiest to remember are aspartic acid, glumatic acid, glycine, and proline. The acids have the almost the same structure, but missing one extra carbon (w/ hydrogens). Glycine has only the H atom for its R group, while proline has a unique pentagon ring.