Amino Acids Overview

Overview

This lesson explains how to effectively memorize amino acids, focusing on drawing their structures and understanding how R groups define their properties.

Memorization Strategy

• Practice drawing each amino acid structure to memorize them effectively.
• All amino acids have a central carbon with four groups: amino, carboxyl, hydrogen, and R (side chain).

Amino Acid Structure Basics

• Central (chiral) carbon bonds to an amino group, a carboxylic acid group, a hydrogen, and an R group.
• The R group (side chain) varies and determines each amino acid's properties.

Examples of Amino Acids by Type

Nonpolar (Hydrophobic) Amino Acids

• Glycine (Gly): R group is H; simplest structure.
• Alanine (Ala): R group is CH₃ (methyl).
• Valine (Val): R group is isopropyl (CH-(CH₃)₂).
• Leucine (Leu): R group is isobutyl (CH₂-CH-(CH₃)₂).
• Isoleucine (Ile): R group is sec-butyl (CH-(CH₃)-CH₂-CH₃).
• Methionine (Met): Contains sulfur; R group is CH₂-CH₂-S-CH₃, nonpolar.
• Proline (Pro): Ring structure; nitrogen is part of side chain; nonpolar, heterocyclic.
• Phenylalanine (Phe): Benzene ring on methyl; aromatic and nonpolar.
• Tryptophan (Trp): Two fused rings (indole); aromatic, mostly nonpolar.

Polar (Hydrophilic) Amino Acids

• Serine (Ser): R group is CH₂-OH; hydroxyl makes it polar.
• Threonine (Thr): R group is CH(OH)-CH₃; contains polar and nonpolar portions, overall polar.
• Cysteine (Cys): R group is CH₂-SH (thio group); can form disulfide bonds, generally polar.
• Asparagine (Asn): R group is CH₂-amide; polar due to amide group.
• Glutamine (Gln): R group is CH₂-CH₂-amide; polar due to amide group.
• Tyrosine (Tyr): Phenyl group with OH; contains both polar (OH) and nonpolar parts.

Acidic (Negatively Charged) Amino Acids

• Aspartate (Asp): R group is CH₂-COOH; extra carboxyl group (acidic, negatively charged).
• Glutamate (Glu): R group is CH₂-CH₂-COOH; extra carboxyl group (acidic, negatively charged).

Basic (Positively Charged) Amino Acids

• Lysine (Lys): R group is (CH₂)₄-NH₂; basic and positively charged.
• Arginine (Arg): R group contains three methylene groups and a guanidinium group; basic, positively charged.
• Histidine (His): R group is imidazole ring; basic, aromatic, heterocyclic, and charged.

Key Terms & Definitions

• Amino Acid — Organic molecule with central carbon, amino group, carboxyl group, hydrogen, and variable R group.
• R Group — The side chain on an amino acid that determines its properties.
• Nonpolar Amino Acid — Amino acid with hydrocarbon R groups; hydrophobic.
• Polar Amino Acid — Amino acid with R groups that form hydrogen bonds; hydrophilic.
• Aromatic Amino Acid — Contains a benzene or similar ring structure in R group.
• Charged Amino Acid — Side chain charged at physiological pH; can be acidic (negative) or basic (positive).
• Heterocyclic Amino Acid — Amino acid whose side chain ring contains atoms other than carbon.

Action Items / Next Steps

• Practice drawing each amino acid structure multiple times from memory.
• Compare similar amino acids to reinforce understanding of structural differences.
• Test yourself by pausing before viewing each new structure and drawing from memory.