Cell Cycle (PDF)

The cell cycle dr. Reham Abd Al Monsif UNIT V Eukaryotic cell division consists of: 1- Mitosis: The division of the nucleus 2- Cytokinesis: The division of the cytoplasm  THE CELL CYCLE...

The cell cycle dr. Reham Abd Al Monsif UNIT V Eukaryotic cell division consists of: 1- Mitosis: The division of the nucleus 2- Cytokinesis: The division of the cytoplasm  THE CELL CYCLE (A) Interphase (about 90 % of the cell cycle): Can be divided into 3 sub-phase 1- G1 phase (first gap) 2- S phase (synthesis) 3- G2 phase (second gap) (A) Mitosis (M) (B) Cytokinesis INTERPHASE Cell growth and DNA synthesis occur during interphase Consists of G1 phase, S phase, G2 phase G1 AND G0 PHASES G1 phase: growth phase and a preparation time for DNA synthesis RNA and protein synthesis also takes place Duplication of organelles and structures G0 not cycling cells (resting state) The restriction point, if passed cell commit a cell to enter S phase (DNA synthesis) S PHASE Synthesis of nuclear DNA (DNA replication) Each chromosome form a sister chromatid Actively cycling cells spend 6 hours in S phase G2 PHASE Gap between completion of S and start of Mitosis It is safety period to ensure the completion of DNA synthesis before Mitosis (nuclear division) Checkpoint (intracellular regulatory molecules assess nuclear integrity) (B) MITOSIS (NUCLEAR DIVISION) It is continuous process Mitosis is conventionally divided into five phases: 1- Prophase 2- Prometaphase 3- Metaphase 4- Anaphase 5- Telophase  Summary of Mitosis 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: each 2-chromatid chromosome becomes teo 1-chromatid chromosomes - chromosomes pulled to opposite poles by the spindle  Telophase: - chromosomes de-condense - Nuclear envelope reappears - Cytokinesis: the cytoplasm is divided into cells (C) CYTOKINESIS Completion of cell cycle Cytoplasmic division Actin microfilaments ring forms cleavage furrow Cleavage furrow begins in anaphase