DNA Structure
Two antiparallel sugar-phosphate strands held together by hydrogen-bonded base pairs (A=T two bonds, G≡C three bonds). RNA differs by ribose sugar, uracil, and single-stranded form.
Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C). RNA replaces T with Uracil (U).
Pairing: A pairs with T (or U) — two H-bonds. G pairs with C — three H-bonds. GC-rich regions melt at higher temperature.
Polarity: Strands are antiparallel — one runs 5'→3', the other 3'→5'. DNA polymerase only adds nucleotides at the 3' end.
Scale: The human genome is ~3.2 billion base pairs across 23 chromosome pairs, encoding ~20,000 protein-coding genes.
Helix: One full turn of the B-form helix is ~10.5 base pairs and ~3.4 nm long. Major and minor grooves are where most proteins bind.
Codon Table
All 64 mRNA codons. AUG starts (Met). UAA, UAG, UGA stop. The code is degenerate — most amino acids are encoded by more than one codon.
Transcribe & Translate
Paste a DNA template (or coding) strand or an mRNA. The page transcribes to mRNA and walks the codons. Stop codons end the run.
Reading frame:
Strand:
Punnett Square
Pick parent genotypes and watch the offspring ratios fall out. Capitals are dominant; lowercase recessive.
Parent 1 (mother)
Parent 2 (father)
Inheritance Patterns
Most real-world traits are not Mendelian. These are the seven patterns you'll see most.
Mutations
Pick a mutation and watch what happens to the protein sequence below. The sample sequence encodes the first nine amino acids of human β-globin.
Drill
Four modes — codon→AA, AA→codons, Punnett ratios, inheritance patterns.
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Daily Challenge
Eight questions. Same set for every user; new set at midnight local time.
Today's set
Question 1 / 8