Cell Replication

Binary Fission is how prokaryotic cells (bacteria) copy themselves. The DNA copies and separates, and the cell wall splits the cell in half. Prokaryotes

In Eukaryotic cells, it’s more complicated… One section of DNA is called a gene. –All cells within one organism have the same genes. –What makes one cell different from another cell is that different genes are turned on or off in different cells.

Mitosis Cells divide to make more cells. The new cells made during mitosis are called daughter cells. DNA in a cell is bundled into chromosomes. Humans have 46 chromosomes, 23 from each parent. Every cell has the same 46 chromosomes.

Chromosomes Chromosomes are bundles of DNA packaged around proteins. Each chromosome has a centromere in the center.

More Chromosomes Each half of the chromosome is called a chromatid. In mitosis, the two chromatids of each chromosome separate, with each chromatid going into a daughter cell. Check for Understanding

Label the Parts of the Chromosome Use your notes from the last two slides to label this picture:

Prophase In prophase, the DNA condenses into chromosomes and the nuclear membrane starts to disappear.

Metaphase In Metaphase, the chromosomes line up in the middle of the cell.

Anaphase In anaphase, the chromatids are pulled apart to opposite sides of the cell.

Telophase In telophase the spindle dissolves and the nuclear membranes reforms. The cytoplasm and other cell organelles are divided up.

Cytokinesis In Cytokinesis, the cell membrane pinches apart to form two separate cells.

Machinery of Mitosis The centrioles in the cell attach spindle fibers to the centrosomes on the chromosomes. The spindle fibers pull the sister chromatids apart, putting one chromatid on each side of the cell.

Check for Understanding Prophase: Chromosomes condense Nuclear envelope disappears centrosomes move to opposite sides of the cell Spindle forms and attaches to centromeres on the chromosomes Metaphase Chromosomes lined up on equator of spindle centrosomes at opposite ends of cell Anaphase Centromeres divide: the 2 chromatids of each chromosome are split apart These chromatids are pulled to opposite poles by the spindle Telophase Chromosomes de-condense Nuclear envelope reappears Cytokinesis: the cytoplasm is divided into 2 cells