Cell Division

DNA Replication and Cell Division

DNA must replicate so that during cell division, the new cells formed each receive a complete set of genetic information

Cells must divide for:• reproduction (e.g. unicellular organisms)• growth (e.g. 1 fertilized egg --> human of ~100

trillion cells)• healing and tissue repair (e.g to replace dead or

damaged cells)

Mitosis

The Cell Cycle

Mitosis occurs when a parent cell divides to produce two identical daughter cells

Mitosis refers to the process of dividing the nuclear material

Cytokinesis refers to the process of separating the cytoplasm and its contents into equal parts

The cell cycle consists of interphase, mitosis, and cytokinesis

Interphase G1 phase: cell grows

S phase: DNA is replicated

G2 phase: cell prepares for mitosis

DNA is visible in the nucleus as strands called chromatin

Phase 1 of Mitosis: Prophase Centrioles move to

opposite poles of the cell

Chromatin condenses and shortens into chromosomes

Spindle fibres form between the centrioles

Nuclelar membrane starts to dissolve

Phase 2 of Mitosis: Metaphase Spindle fibres attached

to centrioles pull chromosomes into place

Chromosomes line up across the equator of the cell

Centromeres hold the chromosomes perpendicular to the spindle fibres

Phase 3 of Mitosis: Anaphase Chromatids (single-

stranded chromosomes) separate at the centromere

Chromatids are pulled to opposite poles by spindle fibres

Phase 4 of Mitosis: Telophase

Two nuclear envelopes form

Single-stranded chromosomes uncoil to become chromatin

Cytokinesis

occurs after telophase: organelles are distributed between the two daughter cells and the cell membrane pinches inward

Summary

Interphase Prophase

Metaphase

Anaphase

Telophase

Mitosis in Onion Root Cells