The Cell Cycle

1. The Cell Cycle

2. The Stages of the life of the cell Involve: 1. Metabolic activities 2. Division What is the cell cycle?

3. Purpose of Cellular Division • -Asexual reproduction of cells • Development of multicellular organisms • Repair and renew cells that die from normal • wear and tear or accidents

4. In eukaryotes, the genome consists of several chromosomes In prokaryotes, the genome is often a single long DNA molecule (chromosome) Cell Division and DNA When cells divide, duplicate copies of DNA ( genome) Are sent to each cell

5. Human somatic cells ( body cells) have 46 chromosomes- 23 pairs Every eukaryotic species has a characteristic number of chromosomes in the nucleus • When not packaged, DNA is a long, • thin strand (chromatin) associated • With proteins called HISTONES

6. Histones- protein spheres DRAW

7. Each duplicated chromosome consists of two sister chromatids which contain identical copies of the chromosomes DNA As they condense, the region where the strands connect shrinks to a narrow area called the centromere Chromosomes Centromere

8. Stages of the Cell Cycle • Divided into 2 main stages • Interphase- G1, S, G2 • Mitotic Phase- M

9. G1 phase- growth S phase- “synthesis”, chromosomes copied G2 phase- cell completes preparations for cell division Mitosis- division of cells to 2 daughter cells Stages of the Cell Cycle

10. The Stages of Mitosis • Prophase • Chromosomes condense and nuclear membrane disappears • Each chromosome appears as a sister chromatid- X SHAPE FORMATION • Mitotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell. • THIS IS USED TO PULL THE CHROMOSOMES APART

11. The Stages of Mitosis • Prometaphase • Breakdown of nuclear envelope into small fragments • Microtubules interact with the chromosomes • Bundles of microtubules extend from each pole toward the middle • Each of the 2 chromatids has a specialized structure called a kinetochore. Some microtubules attach to the kinetochore to begin movement Kinetochore

12. The Stages of Mitosis • Metaphase • Centrosomes are now at opposite poles of the cell • Chromosomes convene on the metaphase plate-immaginary line between poles • Centromeres aligned and the kinetochores of the sister chromatids are attached to microtubules coming from opposite poles of the cell • The microtubules are called spindles b/c of their shape

13. The Stages of Mitosis • Anaphase • Paired centromeres of each chromosome separate, freeing sister chromatids • Each chromatid is considered a full fledged chromosome • The once joined sisters begin to move towards opposite poles of the cell • By the end of anaphase, the 2 poles of the cells have equivalent and a complete collections of chromosomes

14. The Stages of Mitosis • Telophase • Nonkinetochore microtubules elongate the cell, and daughter nuclei form at the poles of the cell • Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope • Chromatin fiber becomes less tightly coiled • CYTOKINESIS- division of cytoplasm takes place shortly after end of mitosis

15. Cytokinesis • Cleavage furrow forms which pinches the cell into 2 parts, near the old metaphase plate. • On the cytoplasmic side of the furrow is a contractile ring of microfilaments which contracts to pull apart the cells like a drawstring • Finally 2 separate cells are created