At the heart of life is DNA.
DNA is one of life's essential building blocks. Found inside nearly every cell in your body, it carries the instructions that help cells grow, repair themselves, and do their work.
An illustrated story of DNA replication
One becomes two. The hidden story of life.
Every day, a quiet miracle happens inside you.You do not see it, but new cells are being made all the time. Before one cell can become two, its DNA must copy itself. Deep inside, a precise choreography begins. This is the story of DNA, and how life carries itself forward.
Begin with oneBefore the cell divides, every letter must be copied.
Human DNA is far too long to copy from one end. So the work begins at many points along the chromosomes. We will follow one.
First, the twist must let go.
An enzyme releases the tension ahead. Then helicase opens the double helix into two strands, while small proteins hold the exposed DNA apart.
Each half remembers the whole.
Each old strand becomes a guide. A always pairs with T, and C with G. With this simple rule, the cell can rebuild both missing sides.
Every copy needs a beginning.
Primase lays down a tiny RNA starter called a primer. DNA polymerase attaches at its end and begins adding matching letters.
One side flows. The other follows in pieces.
DNA polymerase can build in only one direction. So one new strand grows in a continuous line, while the other is built in short pieces as the fork opens.
The pieces become a whole.
Behind the moving fork, the RNA primers are removed and replaced with DNA. Ligase seals the fragments into one strand, while polymerase checks each new letter as it works.
One molecule. Two complete copies.
Each helix holds one original strand and one newly made strand. Now the cell is ready to divide, carrying the same instructions forward.
At the heart of life is DNA.
DNA is one of life's essential building blocks. Found inside nearly every cell in your body, it carries the instructions that help cells grow, repair themselves, and do their work.
Before the cell divides, every letter must be copied.
Human DNA is far too long to copy from one end. So the work begins at many points along the chromosomes. We will follow one.
First, the twist must let go.
An enzyme releases the tension ahead. Then helicase opens the double helix into two strands, while small proteins hold the exposed DNA apart.
Each half remembers the whole.
Each old strand becomes a guide. A always pairs with T, and C with G. With this simple rule, the cell can rebuild both missing sides.
Every copy needs a beginning.
Primase lays down a tiny RNA starter called a primer. DNA polymerase attaches at its end and begins adding matching letters.
One side flows. The other follows in pieces.
DNA polymerase can build in only one direction. So one new strand grows in a continuous line, while the other is built in short pieces as the fork opens.
The pieces become a whole.
Behind the moving fork, the RNA primers are removed and replaced with DNA. Ligase seals the fragments into one strand, while polymerase checks each new letter as it works.
One molecule. Two complete copies.
Each helix holds one original strand and one newly made strand. Now the cell is ready to divide, carrying the same instructions forward.
Two complete copies
Life carries itself forward.
The cell can now divide. Each new cell receives the same instructions, ready to grow, repair, and begin the cycle again.
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