The nine nonpolar amino acids are glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, and tryptophan. That’s a lot to keep straight, but a combination of mnemonics, subgrouping, and understanding why each one is nonpolar makes the list stick far better than rote repetition.
The GAVLIMP FW Mnemonic
The most widely used memory aid pulls the single-letter codes of all nine nonpolar amino acids into one chunk: G A V L I M P F W. A popular version shortens this to “GAVLIMP” plus the two aromatics, F and W, on the side. Each letter maps to one amino acid:
- G = Glycine
- A = Alanine
- V = Valine
- L = Leucine
- I = Isoleucine
- M = Methionine
- P = Proline
- F = Phenylalanine
- W = Tryptophan
Say “GAV LIMP” out loud a few times and it starts to feel like a name. Then tack on “FW” (think “forward”) to capture phenylalanine and tryptophan. Some students prefer building a sentence instead: “Grandma Always Visits London In May, Preferring Fine Weather.” Any sentence that maps to G-A-V-L-I-M-P-F-W works, and inventing your own tends to be more memorable than borrowing someone else’s.
Split Them Into Three Subgroups
Mnemonics get you through an exam, but grouping the nine by structure helps you actually understand what you’re memorizing. Nonpolar amino acids fall neatly into three families.
The Small Aliphatics: G, A, V, L, I
These five have simple hydrocarbon side chains with no rings, no sulfur, and no special tricks. Glycine is the smallest amino acid of all, with just a single hydrogen as its side chain. Alanine adds one methyl group. Valine, leucine, and isoleucine are the “branched-chain” amino acids you may have seen on supplement labels. Their side chains are short, branching carbon skeletons that repel water the way oil does. On the Kyte-Doolittle hydrophobicity scale (a standard ranking of how strongly each amino acid avoids water), isoleucine scores highest of all 20 amino acids at 4.5, with valine at 4.2 and leucine at 3.8.
The Oddballs: M and P
Methionine and proline are nonpolar but structurally distinctive, which actually makes them easier to remember once you know their quirks.
Methionine contains a sulfur atom buried in the middle of a carbon chain. You might expect sulfur to make it polar, but sulfur and carbon have nearly identical electronegativities, so the side chain behaves like a hydrocarbon. Methionine is also the “start” amino acid, the first one placed during protein synthesis. That double identity (nonpolar + start codon) is hard to forget.
Proline is the only amino acid whose side chain loops back and bonds to its own backbone nitrogen, forming a rigid ring. This kink makes proline a helix-breaker in protein structure. If you remember proline as “the one that bends the chain,” you’ll also remember it belongs in the nonpolar group, because that ring is pure hydrocarbon.
The Aromatics: F and W
Phenylalanine and tryptophan both carry bulky ring structures. Phenylalanine is literally “alanine with a phenyl ring” (a six-carbon benzene ring), which is how it got its name. Tryptophan has an even larger double-ring (indole) structure. Both rings are made entirely of carbon and hydrogen, making them hydrophobic despite their size. Tryptophan scores slightly negative on the Kyte-Doolittle scale (-0.9) because of its size and a nitrogen buried in the ring, but it still behaves as nonpolar in protein folding and is consistently classified with this group.
Why “Nonpolar” Matters for Memory
Understanding the underlying logic reinforces the list better than any acronym alone. A side chain is nonpolar when it contains only carbon-hydrogen bonds (or, in methionine’s case, a carbon-sulfur bond with matched electronegativity). These side chains can’t form hydrogen bonds with water, so they’re pushed away from it.
Inside a folded protein, nonpolar amino acids cluster together in the interior, much like oil droplets merging in water. Polar and charged amino acids arrange themselves on the protein’s surface where they can interact with the watery environment of a cell. This sorting is one of the main forces that drives a protein into its three-dimensional shape. So when you’re trying to recall whether an amino acid is nonpolar, ask yourself: “Would this side chain hide inside a protein, away from water?” If the side chain is just carbons and hydrogens (or methionine’s near-equivalent), the answer is yes.
Memory Tricks That Use Structure
Flash cards and mnemonics work, but linking the name to the structure cements memory at a deeper level. Here are practical associations for the trickier members of the list.
Glycine: The simplest amino acid. Its side chain is just a hydrogen atom, so there’s nothing there to be polar. Think “G for gone” because the side chain is essentially gone.
Valine, Leucine, Isoleucine: These three are the branched-chain trio. Their structures look like little forks or Y-shapes. Leucine and isoleucine are isomers of each other (same atoms, different arrangement), which is why isoleucine has “iso” in the name. If you can draw leucine, just rearrange the branch point and you have isoleucine.
Phenylalanine: The name literally tells you what it is: phenylalanine = phenyl (benzene ring) + alanine. Picture alanine with a big ring bolted onto it.
Tryptophan: The largest amino acid by molecular weight, with a distinctive double ring. Many students remember it as “the turkey amino acid” from the popular (though somewhat exaggerated) association with post-Thanksgiving drowsiness. It’s also the only amino acid with the single-letter code W, which you can think of as “W for wide” since it has the bulkiest side chain.
A Quick Self-Test Strategy
Once you’ve practiced the mnemonic and the subgroups, test yourself by writing all 20 amino acids and sorting them into nonpolar, polar uncharged, positively charged, and negatively charged. The nonpolar group is the largest at nine members, which means once you’ve locked it in, you’ve handled nearly half the list. Start by writing G-A-V-L-I-M-P-F-W from memory, then check each one against the logic: does it have a hydrocarbon or aromatic side chain with no oxygen, nitrogen, or ionizable group exposed? If yes, it belongs.
Most students find that after three or four rounds of writing the list, grouping by structure, and self-testing, the nine nonpolar amino acids become automatic. The mnemonic gets you started, the structural reasoning keeps you from second-guessing yourself, and the self-test closes any gaps.