cell division. dna replication and cell division dna must replicate so that during cell division,...
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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
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