Binary Fission

Binary fission

How prokaryotes reproduce: copy the single circular chromosome, then split into 2 identical cells

Binary fission Step 1

Cell has 1 circular chromosome with 1 ORI (origin of replication)

Binary fission Step 2

DNA replication starts at the ORI and goes both directions, making 2 ORIs

Binary fission Step 3

The 2 ORIs move to opposite ends of the cell while the cell gets longer

Binary fission Step 4

Replication finishes, cell is about 2x its size. Membrane pinches inward and a new cell wall forms in the middle

Binary fission Step 5

Cell splits into 2 genetically identical daughter cells, each with a full chromosome

Binary fission timing fact

E. coli can divide every 20 min; DNA replication takes 19 of those minutes

DNA replication: when

Prokaryotes: right before and during binary fission. Eukaryotes: S phase of interphase

DNA replication Step 1

Replication begins at the ORI (origin of replication). Prokaryotes have 1 ORI; eukaryotes have many along each chromosome

DNA replication Step 2

Replication moves in both directions away from the ORI until the whole DNA molecule is copied

DNA replication Step 3

Result: 2 identical DNA molecules. In eukaryotes, each chromosome now has 2 sister chromatids

DNA replication Step 4

Cohesins hold the sister chromatids together at the centromere until anaphase

DNA replication: key takeaway

DNA amount doubles but chromosome number stays the same (46 chromosomes, 92 DNA molecules in humans