Purpose of Cell Division Growing multicellular organisms - a means of growth. Adult multicellular organisms - a means of repair or asexual reproduction. Unicellular organisms - an important means of reproduction.

Cells with a nucleus divide by Mitosis.

Overview of Cell Division

The Cell Cycle

Phases of The Cell Cycle 1. Interphase The cell carries out its work and duplicates its chromosomes. This includes the phases G1, S and G2

Phases of The Cell Cycle G1 - normal cell functions, and cell growth. - nuclear membrane is visible. - chromatin is uncoiled, and within the nucleus.

Phases of The Cell Cycle S -DNA replication - The cell receives a signals to begin replication - DNA molecule unwinds. - DNA is replicated, by a group of enzymes. - Centrosome replicates

DNA Replication Each of the single strands of the original molecule serves as a template for the creation of a second DNA strand. Free-floating DNA bases will bond, one base at a time, with bases on the original strand(A-T, G-C)

Phases of The Cell Cycle G2 –cytoplasmic growth and preparation for cell division

Mitosis – division of DNA Cytokinesis – division of cytoplasm

Mitosis and Cytokinesis 1

Mitosis and Cytokinesis 2

Mitosis 1.Prophase Chromatin (DNA) coils into chromosomes which appear as rods. Nuclear membrane disintegrates. The 2 centrosomes start moving apart to opposite sides of the cell. Microtubules form a mitotic spindle between the centrosomes. Chromosomes start moving toward the equator of the cell.

Chromatin becomes Chromosomes

centromere

Mitosis 2. Metaphase Chromosomes line up at the equatorial plane of the spindle. The 2 chromatids start to separate.

Mitosis 3.Anaphase: Chromatids move toward opposite poles of the cell.

Mitosis 4.Telophase (the reverse of prophase.) Chromosomes uncoil. New nuclear membrane is formed.

Cytokinesis cytoplasmic division. Two new cells are created The cells are in the G1 phase of the cell cycle

Variations in Cell Division 1. Animal cell: centrioles (2 in each centrosome) 2. Plant cell: Formation of a cell plate, from small vesicles that had clustered at the equator The cell plate grows to become a new cell wall.

Plant Cell Cytokinesis

Asexual Reproduction in animals (generation of multiple individuals) Lower organisms only: (hydra, worms) Regeneration in animals (replacement of part of an organism) Starfish, crabs, human liver

Asexual reproduction of plants (vegetative propagation). budding runners (spider plant) rhizomes (fern) sprouts (potato) hyacinth bulbs cuttings