INTERACTIVE PATHWAY · HOW CELLS COPY
DNA replication & cell division
First a cell copies its DNA. Then it sorts the copies and splits. Follow either story at your own pace.
FIRST · COPY THE DNA
Watch two strands become two copies
The copy happens in the S phase, before the cell divides.
THE BIG PICTURE · TAP ANY STOP
From one DNA molecule to two
Choose a stop to update the lesson below, or follow the story in order.
Step 1 of 6: Start with DNA.
Start with DNA
Two strands hold matching bases.
DNA has two strands. A pairs with T, and C pairs with G. Before a body cell divides, it makes a copy of its DNA so each new cell can receive a set.
Look closer at the matching DNA letters
Before copying both strands are old
A pairs with T · C pairs with G. Old strands are dark; newly built strands are copper. This picture shows base pairing, not the real speed or direction of a replication fork.
What to remember: copying makes two DNA molecules. Each gets an old strand and a new strand. A cell can copy DNA without making a protein from every gene.
NEXT · SORT AND SPLIT
Follow the cell cycle
S phase copies the DNA. Mitosis sorts it. Cytokinesis splits the cell.
THE BIG PICTURE · TAP ANY STOP
The cell grows, copies, sorts and splits
Choose a stop to update the lesson below, or follow the story in order.
Step 1 of 5: G1 · Grow.
G1 · Grow
The cell gets ready.
The cell grows and does its normal work. Its chromosomes have not yet been copied for this round of division.
