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