DNA & RNA Bases — Chemistry Mnemonic
Target: mnemonic for DNA RNA bases nucleotides
Why is this hard to memorize?
DNA and RNA bases are tested in both Chemistry (biomolecules) and Biology (molecular biology) in NEET. DNA has four bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T). RNA replaces Thymine with Uracil (U). Base pairing follows strict rules: A-T (or A-U in RNA) with 2 hydrogen bonds, and G-C with 3 hydrogen bonds. You also need to know: purines (A, G — double ring) vs pyrimidines (C, T, U — single ring), Chargaff's rules, and the sugar difference (deoxyribose in DNA, ribose in RNA). These facts are tested so frequently that instant recall is essential.
Classic mnemonics you should know
"AT the GC — A pairs with T, G pairs with C"
"AT the GC" or "Apple Tree, Green Car" — A always pairs with T (2 H-bonds) and G always pairs with C (3 H-bonds). In RNA, T is replaced by U, so A pairs with U.
"PURe As Gold — PURines = Adenine, Guanine (double ring, bigger)"
Purines(PURe) = A and G. Pyrimidines = C, T, U (CUT the PY). Pure As Gold → A and G are purines. Remember: puRine has R = two Rings; pyrimidine has Y = one ring (Y looks like a fork, simpler).
"A-T = 2 bonds (A and T have fewer letters combined). G-C = 3 bonds (G≡C, the triple bar)"
A-T has 2 hydrogen bonds. G-C has 3. To remember: "A-T = 2" (the letters A and T come before C and G alphabetically → fewer). Or: G-C is "stronger" → 3 bonds → higher melting point for GC-rich DNA.
The complete list
- Adenine (A) — Purine
- Guanine (G) — Purine
- Cytosine (C) — Pyrimidine
- Thymine (T) — Pyrimidine (DNA only)
- Uracil (U) — Pyrimidine (RNA only)
- A-T pairing (2 H-bonds)
- G-C pairing (3 H-bonds)
- DNA sugar: Deoxyribose
- RNA sugar: Ribose
Frequently asked questions
How do I remember which bases are purines and which are pyrimidines?
"PURe As Gold" — Purines are Adenine and Guanine (double-ring structures). Pyrimidines are Cytosine, Thymine, and Uracil — "CUT the Py(e)" helps remember C, U, T are pyrimidines.
Why does DNA use Thymine but RNA uses Uracil?
Thymine is a methylated form of Uracil (has an extra CH₃ group). DNA uses Thymine because it provides better protection against mutations — if Cytosine deaminates, it becomes Uracil, and the repair system can detect this error only if Uracil is not normally present in DNA. RNA does not need this extra protection because it is short-lived.
What is Chargaff's rule and how is it tested in NEET?
In double-stranded DNA: %A = %T and %G = %C (because of complementary base pairing). So A+G = T+C (purines = pyrimidines). A typical NEET question gives you one percentage (e.g., "A = 30%") and asks you to find the rest: T = 30%, G = C = 20%. Remember: this rule only applies to double-stranded DNA, not to single-stranded DNA or RNA.
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