🧬 DNA

DNA: The Cell’s Instruction Book

DNA stands for Deoxyribonucleic Acid.

It:

• Stores instructions to build and run your body
• Is found in the nucleus of most cells
• Is passed from parents to children

> Every cell in your body (except red blood cells) carries the same DNA.

Think of DNA as a recipe book; cells read its recipes to make proteins.

DNA’s Basic Parts

DNA is built from small units called nucleotides.

Each nucleotide has:

• A sugar
• A phosphate group
• A nitrogen base

There are 4 bases:

• Adenine (A)
• Thymine (T)
• Cytosine (C)
• Guanine (G)

These four letters form the entire genetic code of living things.

The Double Helix Shape

DNA looks like a twisted ladder, called a double helix.

• Sugar and phosphate = sides of the ladder
• Bases = rungs of the ladder

Base-pair rules:

• A always pairs with T
• C always pairs with G

These specific pairings keep DNA stable and easy to copy.

Genes and Chromosomes

• A gene is a segment of DNA with instructions for one protein or trait.
• Chromosomes are long, tightly packed DNA strands.

Humans have:

• 46 chromosomes in most cells
• About 20,000–25,000 genes total

You inherit half your chromosomes from each parent.