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 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 The Cell Cycle

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 Telophase Metaphase Anaphase

Mitosis in Onion Root Cells