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Now you know why DNA is so important!

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Why is DNA important?

▶ 5:27 video · Watch on YouTube

  1. 0:00 Start
  2. 0:53 A twisted ladder
  3. 1:45 Unzip and copy
  4. 2:31 The messenger
  5. 3:34 Reading in threes
  6. 4:26 Why DNA matters

Your turn

Twist, copy and read DNA yourself

Play with DNA!

Each lab is one step from the video. Change things and see what happens.

Each lab isolates one step of the story. The pictures are simplified models, not to scale.

Tap the buttons and see what happens.

1

Seed, cell, DNA

Three scales

Zoom in!

Tap the acorn, the cell or the DNA to zoom from one to the next.

Step from the seed to one of its cells to the molecule that holds the instructions.

Tap the acorn. Then the cell. Then the DNA!

▶ Watch this part
2

Twist the ladder

Ladder or helix

Twist the ladder

Drag across the ladder to twist and untwist it. Which letters always pair up?

Untwist the double helix into a flat ladder: sugar-phosphate sides, base-pair rungs, A–T and C–G.

Drag to twist the ladder. Then untwist it!

▶ Watch this part
3

Rebuild the missing side

Template copying

Fill the gaps

Tap each empty gap until the letter matches the old strand: A with T, C with G.

Each old strand is a template: only one base fits each gap. Rebuild the new strand.

Tap a gap to change its letter. Can you match them all?

▶ Watch this part
4

Copy a gene into RNA

Transcription

Make a copy

Copy the gene one letter at a time. What does RNA put opposite an A?

Build messenger RNA from the DNA template. Note U wherever DNA would pair with T.

Tap to copy the recipe, one letter at a time.

▶ Watch this part
5

Change one letter

Point changes

Tap any RNA letter to change it. Can one letter change the whole protein?

Change single bases. Some codon changes swap an amino acid, some change nothing, and some create an early stop.

▶ Watch this part
6

Make a kitten

Half and half

Make a kitten

Tap Make a kitten. Each kitten gets one of every pair from mom and one from dad.

Each offspring gets one chromosome of every pair from each parent (a simplified picture with 4 pairs).

Tap Make a kitten. Some from mom, some from dad!

▶ Watch this part

What is DNA?

DNA is a set of instructions inside living things. It tells an acorn to grow into an oak tree, and it tells your body how to grow into you.

1. Tiny cells

Every living thing is made of tiny cells. Inside each cell is DNA. It is very, very long, but it is packed up super small.

2. A twisted ladder

DNA looks like a ladder, all twisted up. The steps are made of four letters: A, T, C and G. A always holds hands with T, and C always holds hands with G.

3. Unzip and copy

When a cell splits in two, the ladder unzips like a zipper. Each side gets a new matching side, so each new cell gets its own DNA.

4. Recipes for proteins

The order of the letters is like a recipe. A tiny builder in the cell reads the recipe and makes proteins. Proteins build your body and keep it working.

Did you know? You got half of your DNA from your mom and half from your dad. And an oak, a giraffe and you all use the same kind of code!

← More explainers

Why is DNA important? The short answer

DNA (deoxyribonucleic acid) is the molecule that holds the instructions for building and running a living thing.1 It is the hereditary material in humans and almost all other organisms, and nearly every cell in your body carries the same DNA.2 DNA matters for four big reasons:

  1. It stores the instructions. The order of its four chemical letters spells out genes, and most genes are recipes for proteins, the molecules that do most of the work in your body.1
  2. It can copy itself. Before a cell divides, its DNA is copied so each new cell gets a full set. That is how you grow.210
  3. It carries traits to the next generation. You inherited half of your DNA from each parent.1
  4. Almost all life shares the same code. That's strong evidence that all living things on Earth are related.11

That's why an acorn grows into an oak and never a giraffe: the acorn's DNA holds oak instructions.

What is DNA, and where is it found?

In plants, animals and fungi, most DNA sits inside the cell's nucleus. A small amount is also found in mitochondria, the cell's energy makers.12 Each DNA molecule is extremely long and thin, so the cell packs it tightly into bundles called chromosomes. Humans have 23 pairs.1 Stretched end to end, the DNA in just one of your cells would be about 2 meters long, yet it fits inside a nucleus far too small to see without a microscope.12

Your complete set of DNA, your genome, contains about 3 billion bases and about 20,000 genes.13

What is DNA made of?

DNA is a chain of building blocks called nucleotides. Each nucleotide has three parts: a phosphate group, a sugar (deoxyribose) and one of four bases: adenine (A), thymine (T), guanine (G) and cytosine (C).14 The nucleotides link up with the sugar and phosphate alternating, making a long strand.1 Two strands wind around each other to form the famous double helix: a ladder twisted into a spiral.4

What makes up the sides and rungs of DNA?

The sides (the backbone) are sugar and phosphate. The rungs are pairs of bases. MedlinePlus describes it exactly like a ladder: "the base pairs forming the ladder's rungs and the sugar and phosphate molecules forming the vertical sidepieces."2

Part of the "ladder"What it's made ofWhat it does
Sides (backbone)Alternating deoxyribose sugar and phosphate groups4Strong outer rails that hold the letters in order
RungsBase pairs: A with T, C with G2Carry the information; the order of bases is the code
What holds a rung togetherHydrogen bonds: two between A and T, three between C and G9Weak enough to unzip for copying, strong enough to stay paired

The pairing never changes: A always pairs with T, and C always pairs with G.24 Every rung is the same width, so the helix is an even 2 nanometers across, with about 10 base pairs per full turn.9

How does DNA copy itself?

The pairing rule is what makes copying possible. When a cell gets ready to divide, the two strands of the helix separate like a zipper. Each old strand then acts as a pattern, or template: opposite every A only a T fits, and opposite every C only a G fits. New nucleotides snap into place, and the result is two DNA molecules, each with one old strand and one new strand.10 Scientists call this semi-conservative replication. When Watson and Crick published their model in 1953, they noted that the pairing "immediately suggests a possible copying mechanism for the genetic material."10

Copying matters because each new cell needs an exact copy of the DNA in the old cell.2 For more on how cells split, see why do cells divide?

How is RNA different from DNA?

RNA (ribonucleic acid) is DNA's close cousin, with three key differences: it usually has one strand instead of two, its sugar is ribose instead of deoxyribose, and it uses uracil (U) instead of thymine (T).57

DNARNA
Full nameDeoxyribonucleic acidRibonucleic acid
StrandsTwo, twisted into a double helix4Usually one5
SugarDeoxyriboseRibose57
BasesA, T, C, GA, U, C, G (uracil replaces thymine)5
Main jobLong-term storage of the instructionsWorking copies and helpers for making proteins (mRNA, tRNA, rRNA)57
Where (in our cells)Stays in the nucleus (plus a little in mitochondria)7Made in the nucleus, then works out in the cytoplasm7

A handy way to remember it: DNA is the master recipe book that never leaves the library, and messenger RNA is a photocopy of one recipe that you carry to the kitchen. Some viruses even use RNA instead of DNA as their genetic material.5

How does DNA make proteins?

It takes two steps.1

  1. Transcription: enzymes read a gene and build a matching strand of messenger RNA (mRNA). Wherever the DNA has an A, the RNA gets a U.17 (Curious how those enzymes work? See how do enzymes work?)
  2. Translation: the mRNA travels to a ribosome, which reads it three letters at a time. Each group of three is a codon, and each codon stands for one amino acid, or for "stop".67

With four letters in groups of three there are 64 possible codons: 61 code for the 20 amino acids and 3 are stop signals.615 AUG means "start here" and also codes for the amino acid methionine.1115 Most amino acids have more than one codon, and only methionine (AUG) and tryptophan (UGG) have just one.15 The ribosome links the amino acids like beads on a string until it hits a stop codon, and the chain folds into a working protein.11

Protein-coding genes make up only about 1% of human DNA. Much of the rest helps control when, how and how much of each protein is made.1

Who discovered DNA?

The Swiss scientist Friedrich Miescher first found DNA in cell nuclei in the 1860s.8 For decades, many scientists thought DNA was too simple to carry life's instructions and bet on proteins instead.18 Erwin Chargaff then found that the amount of A matches T and C matches G, a clue to the pairing.13

In 1953, James Watson and Francis Crick built the double-helix model.1 They relied on X-ray diffraction images made by Rosalind Franklin in Maurice Wilkins' lab, including the famous "photo 51". Watson saw it without Franklin's knowledge.149 Watson, Crick and Wilkins won the Nobel Prize in 1962. By then Franklin had died, at just 37, and Nobel Prizes are not given after death. Crick later said her contribution had been critical.914

One code for (almost) all life

With only a few minor exceptions, virtually every species uses the same genetic code. The same codon means the same amino acid in a bacterium, an oak tree, a giraffe and you.11 This is so reliable that a horse gene's mRNA put into a tulip cell would make the horse protein. OpenStax calls the single shared code "powerful evidence that all of life on Earth shares a common origin."11 To see how that shared ancestry played out, read how did humans evolve?

Common misconceptions

"Watson and Crick discovered DNA." Miescher found DNA in the 1860s. In 1953 Watson and Crick worked out its shape, using Rosalind Franklin's X-ray data.89
"RNA is just DNA with one strand." It also has a different sugar (ribose) and uses U instead of T.5
"Most of our DNA is genes." Protein-coding genes are only about 1% of it.1
"DNA is only in the nucleus." Mitochondria have a little DNA of their own.1
"Each amino acid has one codon." Most have two to six. Only methionine and tryptophan have just one.15

FAQ

Why is DNA important, in simple words?

DNA holds the instructions a living thing needs to grow, work and reproduce. Its four-letter code spells out genes, and genes are recipes for proteins, the molecules that build your body and keep it running. DNA is also copied every time a cell divides and passed from parents to their young.

How is RNA different from DNA?

There are three main differences. DNA has two strands twisted into a double helix, while RNA usually has just one strand. DNA's sugar is deoxyribose and RNA's is ribose. And DNA uses the base thymine (T), while RNA uses uracil (U) in its place. DNA stores the instructions; messenger RNA is a working copy of one gene that carries the recipe to a ribosome.

What makes up the sides and rungs of the DNA ladder?

The sides (the backbone) are made of alternating sugar (deoxyribose) and phosphate groups. The rungs are pairs of nitrogen bases held together by hydrogen bonds: adenine always pairs with thymine, and cytosine always pairs with guanine.

What is the purpose of DNA?

DNA's job is to store and pass on information. It carries the instructions for making proteins, it can be copied exactly when a cell divides, and it is handed down from parents to offspring, so each generation gets the instructions for building a new organism.

What are the main functions of DNA?

DNA stores genetic information, copies itself (replication) before a cell divides, provides the template for messenger RNA (transcription) so that proteins can be made, and carries inherited traits from one generation to the next. Parts of DNA outside genes help control when and how much of each protein is made.

Who discovered DNA?

Friedrich Miescher first found DNA in cell nuclei in the 1860s. Its double-helix shape was worked out in 1953 by James Watson and Francis Crick, who relied on X-ray images made by Rosalind Franklin in Maurice Wilkins' lab at King's College London.

Why is DNA important today?

Knowing how DNA works lets scientists understand how living things grow and are related, trace how genes are turned into proteins, and study how organisms change over time. Because almost all life shares the same genetic code, what we learn in one organism often applies to many others.

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Sources

  1. NIH National Human Genome Research Institute, Deoxyribonucleic Acid (DNA) Fact Sheet
  2. MedlinePlus Genetics (NIH), What is DNA?
  3. MedlinePlus Genetics (NIH), What is a gene?
  4. NHGRI Talking Glossary, Double Helix
  5. NHGRI Talking Glossary, Ribonucleic Acid (RNA)
  6. NHGRI Talking Glossary, Codon
  7. OpenStax Biology 2e, 3.5 Nucleic Acids
  8. OpenStax Biology 2e, 14.1 Historical Basis of Modern Understanding
  9. OpenStax Biology 2e, 14.2 DNA Structure and Sequencing
  10. OpenStax Biology 2e, 14.3 Basics of DNA Replication
  11. OpenStax Biology 2e, 15.1 The Genetic Code
  12. OpenStax Concepts of Biology, 9.1 The Structure of DNA
  13. Nature Education Scitable, Discovery of DNA Structure and Function: Watson and Crick
  14. Nature Education Scitable, Rosalind Franklin: A Crucial Contribution
  15. Encyclopaedia Britannica, Genetic code