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DNA Decoded

Crack the molecule of life: the double helix, the four bases and how their order spells out every protein you make.

⏱️ 10 min 🎯 13 activities Teachers Not yet rated Students Not yet rated

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What you'll cover

DNA Decoded 🧬

Inside almost every one of your cells is a molecule that spells out how to build **you**: **DNA**. Decode its structure, the four-letter alphabet it uses, and how the order of those letters becomes the proteins that run your body.

DNA, genes and chromosomes 🧵

The genetic material in the nucleus is **DNA**. It is organised into structures called **chromosomes** — each a very long DNA molecule. A **gene** is a small **section** of a chromosome (a section of DNA) that codes for a particular sequence of amino acids — and so for a specific **protein**.

What is a gene?

Which best describes a **gene**?

  • A small section of DNA that codes for a specific protein
  • The entire genetic material of an organism
  • A type of cell
  • A finished protein molecule

The double helix 🔬

DNA is a **polymer** made of **two strands** coiled into a **double helix**. Each strand is a chain of small units called **nucleotides**. A nucleotide has three parts: a **sugar**, a **phosphate** and a **base**. The sugars and phosphates form the **backbone**; the bases stick inwards. There are **four** bases: **A, T, C and G**.

Label the DNA

An interactive activity.

Bases pair up 🔗

The two strands are held together by their bases, and the pairing is **fixed** — this is **complementary base pairing**: • **A** always pairs with **T** • **C** always pairs with **G** So if you know the bases on one strand, you know the other.

Pair them up

In DNA, the base A always pairs with _____, and the base C always pairs with _____.

T G A U

Find the partner

On one DNA strand there is a base **G**. Which base sits opposite it on the other strand?

  • C
  • T
  • A
  • G

The code of three 📖

How does a base sequence build a protein? The **order** of the bases is a code. Every group of **three bases** (a **codon**) codes for **one amino acid**. Chain the amino acids in that order and you get the protein. Interestingly, **most** of your DNA does **not** code for proteins — much of it controls **gene expression** (which genes are switched on).

How many bases?

In the genetic code, how many bases code for a single amino acid?

  • Three
  • One
  • Two
  • Four

Genome and mutations 🌍

The **genome** is the **entire** genetic material of an organism. Mapping the whole human genome helps scientists find genes linked to disease, treat inherited disorders, and trace human migration. DNA also changes: a **mutation** is a change to the base sequence. Mutations happen continuously — **most have no effect** on the protein, but occasionally one alters the protein's shape and how it works.

True of DNA?

Pick the TWO correct statements.

  • The genome is all of an organism's genetic material
  • Most mutations have no effect on the protein
  • The base G pairs with the base A
  • One base codes for one amino acid

In the exam 🎓

Decoded. Grade-9 habits for DNA: • **DNA** = a double-helix polymer of two strands; a **gene** codes for one protein; the **genome** is all of it. • A nucleotide = **sugar + phosphate + base**; bases pair **A–T** and **C–G**. • **Three bases (a codon) → one amino acid**; most DNA is non-coding; **mutations** change the base sequence (usually with no effect).