How to memorize the 20 amino acids (names, codes and side chains)
The prettysmart teamUpdated 5 min readthe short answer
Sort them first: learn the 20 amino acids in five side-chain groups, with a short sentence that spells each group's one-letter codes. Then learn the 9 one-letter codes that aren't the name's first letter.
Key takeaways
- The groups spell their codes: GAVLIMP, Fat Young Whippersnappers, Santa's Team Crafts New Quilts, Dragons Eat Knights Riding Horses.
- The odd one-letter codes have reasons: F sounds like Fenylalanine, R like aRginine, and K was free and next to L.
- The nine essential amino acids spell PVT TIM HiLL by their names' first letters, not their one-letter codes.
In this guide
The 20 amino acids, grouped
| Amino acid | 1-letter | 3-letter | Group | Essential |
|---|---|---|---|---|
| Glycine | G | Gly | Nonpolar | |
| Alanine | A | Ala | Nonpolar | |
| Proline | P | Pro | Nonpolar | |
| Valine | V | Val | Nonpolar | Yes |
| Leucine | L | Leu | Nonpolar | Yes |
| Isoleucine | I | Ile | Nonpolar | Yes |
| Methionine | M | Met | Nonpolar | Yes |
| Phenylalanine | F | Phe | Aromatic | Yes |
| Tyrosine | Y | Tyr | Aromatic | |
| Tryptophan | W | Trp | Aromatic | Yes |
| Serine | S | Ser | Polar, uncharged | |
| Threonine | T | Thr | Polar, uncharged | Yes |
| Cysteine | C | Cys | Polar, uncharged | |
| Asparagine | N | Asn | Polar, uncharged | |
| Glutamine | Q | Gln | Polar, uncharged | |
| Lysine | K | Lys | Positive (basic) | Yes |
| Arginine | R | Arg | Positive (basic) | |
| Histidine | H | His | Positive (basic) | Yes |
| Aspartate (aspartic acid) | D | Asp | Negative (acidic) | |
| Glutamate (glutamic acid) | E | Glu | Negative (acidic) |
Textbooks draw the lines differently: some move glycine, tyrosine or tryptophan between polar and nonpolar, and OpenStax’s organic chemistry book splits off only the acidic and basic ones. Learn your course’s version; the deck follows this table.
Four sentences that spell the groups
- Nonpolar: GAVLIMP
- Aromatic: Fat Young Whippersnappers
- Polar, uncharged: Santa’s Team Crafts New Quilts
- Charged: Dragons Eat Knights Riding Horses, the two acids first, then the three bases
The 9 one-letter codes to learn
11 codes are just the first letter. C, H, I, M, S and V have their letter to themselves, and A, G, L, P and T got the letter they share because they’re the most common or simplest. The other 9 come with reasons from the committee that set them (IUPAC-IUB), or a trick where it gave none:
| Code | Amino acid | Why |
|---|---|---|
| F | Phenylalanine | Sounds like “Fenylalanine” |
| R | Arginine | Sounds like “aRginine” |
| W | Tryptophan | Its bulky double ring suits the bulky letter W |
| K | Lysine | L went to leucine; K was free and close to L in the alphabet |
| Y | Tyrosine | T went to threonine; Y was one of the few letters still free |
| D | Aspartate | No reason given; think “asparDic acid” |
| E | Glutamate | No reason given; think “gluEtamic acid”, one letter after D like the acid one carbon longer |
| N | Asparagine | No reason given; think “asparagiNe” |
| Q | Glutamine | No reason given; think “Q-tamine” |
The three-letter codes are the first three letters for 16 of the 20. The exceptions: Asn and Gln, where the n marks the amide (Asp and Glu are the acids), Ile and Trp.
The nine essential amino acids
Nine are essential: the body can’t make them, so food has to supply them.
Mnemonic: PVT TIM HiLL is phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine, leucine, lysine.
It spells names, not codes, so watch three of them: P is phenylalanine (code F), the second T is tryptophan (code W) and the second L is lysine (code K). An older version, PVT TIM HaLL, adds arginine, which is only conditionally essential.
The mix-ups that cost points
- Glutamate and glutamine, aspartate and asparagine: the acids (Glu E, Asp D) carry a negative charge; their amides (Gln Q, Asn N) are polar but uncharged.
- Isoleucine and leucine are isomers: same atoms, different arrangement, both nonpolar and essential.
- Histidine’s charge: it’s grouped with the basic amino acids, but its side chain has a pKa near 6, so at the body’s pH most histidine side chains are uncharged.
- Tyrosine and tryptophan: tyrosine (Y) has an OH on its ring and isn’t essential; tryptophan (W) has a double ring and is.
- Cysteine and methionine both contain sulfur, but only cysteine forms disulfide bonds.
A week that makes it stick
Spread it out: the longer you need to remember something, the wider your review gaps should be (Cepeda et al., 2006).
| Day | What to do |
|---|---|
| 1 | The five groups: write the 20 names into their groups from memory, twice |
| 2 | The 9 odd one-letter codes, then the 4 odd three-letter ones |
| 3 | Review both; add the essential nine with PVT TIM HiLL |
| 5 | The whole deck, mixed up |
| 7, then before your exam | The whole deck again; only the misses need more |
Test yourself instead of rereading: 8 of the deck’s 106 cards are below, and the whole deck goes into prettysmart with one code.
Same method, other lists: how to memorize the 12 cranial nerves, the polyatomic ions, the solubility rules, the periodic table, the bones of the body, the Krebs cycle, the unit circle and the presidents in order. They also come up in the chemistry unit that opens anatomy and physiology.
Flashcards: The 20 amino acids
8 of the 106 cards, each checked against this guide's sources. Tap a card to see the answer.
1What is the one-letter code for Lysine?
2What is the one-letter code for Tyrosine?
3Which amino acid is represented by the one-letter code W?
4What is the one-letter code for Glutamine?
5Which amino acid is represented by the one-letter code E?
6What is the three-letter code for Tryptophan?
7What is the biochemical classification of the Histidine side chain?
8Is Tyrosine an essential amino acid in adult humans?
Questions people ask
Is cysteine an essential amino acid?
No. MedlinePlus lists it as conditionally essential, like arginine, glutamine, tyrosine, glycine, proline and serine: usually made by the body, but needed from food during illness and stress. Some textbooks get this wrong.
What is the 21st amino acid?
Selenocysteine (Sec, U). A few proteins, the selenoproteins, build it in at a UGA codon, which is why it is called the 21st amino acid; IUPAC gives it the code U. Lists of the 20 leave it out.
Do I need to memorize the amino acids for the MCAT?
Yes. The AAMC's content outline lists amino acid classification (acidic or basic, hydrophobic or hydrophilic) among the topics, and MCAT prep companies add all 20 names with both codes, because passages refer to amino acids in any of those forms.
Do I need to memorize the structures too?
It depends on the course. Some biochemistry courses expect structures, while AP Biology explicitly doesn't: its course description excludes the structures of specific amino acids. Learn names, codes and groups first, then add structures if your course asks for them.
Sources
- Nomenclature and Symbolism for Amino Acids and Peptides: one-letter symbols (3AA-21), IUPAC-IUB Joint Commission on Biochemical Nomenclature
- Organic Chemistry, 26.1 Structures of Amino Acids, OpenStax
- Amino acids, MedlinePlus, U.S. National Library of Medicine
- Selenocysteine: the 21st amino acid (Böck et al., 1991), Molecular Microbiology
- AP Biology Course and Exam Description, College Board
- What's on the MCAT Exam? Biological and Biochemical Foundations of Living Systems (PDF), AAMC
- Everything you need to know about amino acids for the MCAT, Blueprint Prep
- How to memorize amino acids, Pearson Channels
- Memorizing amino acids: tips, tricks and mnemonics, Dorothy Memory App
- Distributed Practice in Verbal Recall Tasks (Cepeda et al., 2006), Psychological Bulletin