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DNA structure, coding and protein synthesis

Inheritance, variation and evolution • Reproduction

Key concepts

What you'll likely be quizzed about

  • A nucleotide comprises a sugar molecule, a phosphate group, and a single base.
  • The four DNA bases are adenine (A), thymine (T), cytosine (C), and guanine (G).
  • Each nucleotide is formed by the combination of its sugar, phosphate, and attached base.
  • Nucleotides bind together through covalent bonds between the sugar of one and the phosphate of the next, creating a long polymer.
  • The base projects from the sugar–phosphate backbone, forming hydrogen bonds with a complementary base on the opposite strand.

Flashcards

Test your knowledge with interactive flashcards

Why can several codons code for the same amino acid?

Click to reveal answer

The genetic code is redundant, allowing multiple codons to correspond to the same amino acid.

Key notes

Important points to keep in mind

A nucleotide consists of sugar, phosphate, and base; bases are A, T, C, G.

A–T and C–G base pairing forms the double helix; the backbone consists of sugar and phosphate.

Three-base codons correspond to amino acids; several codons can specify the same amino acid.

Transcription generates mRNA in the nucleus; translation assembles polypeptides at ribosomes.

Substitution mutations alter at most one amino acid; insertions or deletions cause frameshift mutations affecting all downstream amino acids.

Protein function relies on the precise sequence of amino acids and proper folding.

Coding variants can modify protein sequences; non-coding variants influence gene expression or may be neutral.

Many mutations are neutral; some can be advantageous or harmful depending on their effect.

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