Multicellular Organisms Cell Teamwork: The Processes of Life.
Purpose of Cell Division Growing multicellular organisms - a means of growth. Adult multicellular...
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Transcript of Purpose of Cell Division Growing multicellular organisms - a means of growth. Adult multicellular...
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
Mitosis1.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