Cell Division

I. Reasons for asexual cell division A. Growth B. Repair C. Reproduction

II. Prokaryotes A. Binary Fission: division of prok. cells into 2 offspring cells DNA Copied Cell begins to divide 2 identical haploid cells formed

III. Eukaryotes - Mitosis A. Cytoplasm and nucleus divide B. Cells go through Mitosis and then Cell division (Cytokinesis) C. Mitosis: The division of the nucleus.

IV. Cell Cycle A. The “life cycle” of the cell 1. Interphase- new cell until mitosis Time between cell divisions 2. 3 parts: G1, S, G2 A. G1=1st growth, normal cellular activity B. S= Synthesis- The DNA is copied C. G2=2nd growth time, getting ready for division

Cell Cycle C. Some cells stay in G1. This is called G0. ( neurons, liver cells) No replication/division of cells All cells must go through G1 checkpoints. The cells have proteins that check to make sure everything is ok before the S phase and moving toward division.

Cell Cycle B. Mitosis- “M phase” – nucleus divides C. Cytokinesis- Splitting of the cytoplasm

How does the cell know how to divide? Cell Division Reproduction Growth Repair Why do cells divide? How does the cell know how to divide? The DNA has the instructions for all of the cell’s activities.

Cell Cycle 3 Parts The sequence of development and division of a cell Interphase - Preparation Mitosis – Cell division Cytokinesis – Splitting Adult human cell: ~24 hrs 18-20 hours in interphase 2 hours in mitosis Embryonic cells: 30 min. How long does it take?

Interphase What happens Cell doubles in size DNA replicates Organelles double in number

Mitosis: PROPHASE What happens DNA forms chromosomes Spindle forms Centrioles move toward opposite poles Nuclear membrane begins to disappear

Mitosis: METAPHASE What happens Nucleus has disappeared completely Chromosomes line up in the middle of the cell “equator” Spindle fibers attach at centromeres

Mitosis: ANAPHASE What happens Centromeres divide Chromatids separate and move to opposite poles Spindle fibers retract to poles

Mitosis: TELOPHASE What happens Nuclear membrane forms around each group of chromosomes Chromosomes unwind Cytokinesis begins

Cytokinesis Cytoplasm divides One cell becomes 2 cells What happens