DNA

What is DNA?

DNA is the set of instructions that make you, you. These instructions tell your body how to create organs and tissues, how to function and what you look like. You can think of DNA as a vast library of instruction manuals. It uses its own “language” to write the story of you that your cells can read.

All living things have DNA in their cells (and some viruses carry it with them, too). You inherit your DNA from your biological parents — you get half from your mother and half from your father.

The letters in DNA stand for deoxyribonucleic acid (“dee-OCK-see-rai-bow-new-CLAY-ick A-sud”). A nucleic acid is an acidic substance found in the nucleus, or “brain” of a cell. “Deoxy” just means it has one less oxygen molecule in its structure than ribonucleic acid, or RNA.

Your genome

All your DNA together is called your genome. Your genome is organized into:

• Chromosomes: These are threadlike structures that separate your DNA into manageable chunks, like individual books of instructions in your DNA library.
• Genes: These are individual sections of your chromosomes that give instructions for specific traits. Think of these like chapters in a book.
• Non-coding DNA: This is the DNA between your genes. It doesn’t code for specific traits, but it still plays an important role. A bit like punctuation in a book, it helps your genes work properly and supports other important cell functions.

What does DNA do?

DNA carries instructions that your cells can read and translate into proteins. These proteins help your body do everything it needs to function — from how your organs work to how you look.

DNA uses its own language to write these instructions. The language is written entirely in four letters: A, C, G and T. There are so many possible combinations for these letters — just like how the letters T-O-P mean something very different than P-O-T — that everyone’s DNA writes a unique story.

DNA’s letters stand for adenine, cytosine, guanine and thymine — groups of molecules that carry instructions on them, usually called bases. Your body reads these letters through:

1. Transcription: RNA — single-stranded nucleic acids that can carry messages — copies the instructions and carries them out of the nucleus.
2. Translation: Tiny decoding machines called ribosomes read the RNA messages and build proteins by linking together amino acids.
3. Post-translational modification, folding and transport: After translation, your cells make further changes to the proteins. Then, they’re ready to help your body work.

Where is DNA located?

Almost all the cells in your body have DNA in their nucleus. The exceptions are red blood cells and platelets (which don’t have a nucleus). Your mitochondria — organ-like structures inside your cells that provide energy — also have DNA. Mitochondrial DNA is usually only inherited from your mother.

What’s the structure of DNA?

DNA is a winding, spiral shape called a double helix. This means it’s actually two corkscrew shapes connected in the middle, like a twisty zipper. In illustrations, it tends to look like a spiral staircase.

DNA is made up of a chain of nucleotides, or building blocks. Each of these building blocks is made up of three parts:

• A nitrogenous base: This is one of four nitrogen-containing bases (adenine, cytosine, guanine and thymine), often just known by the letters A, C, G and T. Each one pairs up in the middle of the corkscrew (As with Ts and Cs with Gs). These are known as base pairs.
• A sugar molecule (deoxyribose): This looks like a pentagon, with five carbon molecules at its five points. It connects the nitrogenous base to the “backbone” — the twisty part — of the DNA.
• A phosphate group: This connects the sugar molecules together to make up the backbone of DNA.

What happens when there are errors in your DNA?

Errors in or damage to your DNA can cause health issues. Your DNA has ways to “proofread” its sequence to make sure there aren’t any errors when it makes more copies of itself. For instance, a base pair might be incorrectly matched. Sometimes, the proofreading process can fail, leading to changes (mutations) in your DNA.

Your DNA can also get damaged during activities in everyday life, including:

• Exposure to the sun
• Inhaling pollution or harmful substances
• Smoking
• Drinking alcohol

DNA damage or changes can lead to:

• Cancer
• Lung disease, heart disease and diseases in other organs
• Skin changes and premature aging
• Fertility issues
• Congenital (present-at-birth) conditions