how do cells grow & reproduce?. in the beginning – one cell most of the organisms start out as...
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How do cells grow & reproduce?
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In the Beginning – One Cell
• Most of the organisms start out as one cell• Humans start out as a single cell, the zygote, formed
by uniting a sperm and egg• The zygote divides to make trillions of cells• During the process of dividing, cells become
specialized to function in the various tissues and organs of the body = differentiation
• Mitosis is the process of cell division in eukaryotic cells
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The Cell Cycle =
Sequences of growth and division of a cell
Two main parts:1. Interphase – growth phase; takes most of the time
2. Mitosis – cell division phase
G1G1
MM
G2G2
SS
Interphase
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G1G1
MM
G2G2
SS
The Cell Life Cycle
Gap 1 - Doubling of cell size, increase in the number of organelles, regular cellular activities
S - Synthesis of DNA
Gap 2 - Final preparation for division
Mitosis - Cell division
G1, S, & G2 = Interphase =
busy time
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S phase – DNA replication
Fig. 3.26
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INTERPHASE:
nuclear envelope is clearly visible
chromatin = uncoiled DNA
http://www.fed.cuhk.edu.hk/~johnson/photomicrographs/mitosis/animal/animal_interphase.htm
nucleolus is still visible
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Interphase
• Metabolic phase• Cell growth• DNA replication• Protein synthesis• Visible nucleus with
CHROMATIN
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Stages of Mitosis
Interphase
Anaphase
Telophase
Metaphase Mitotic spindle
Prophase
Nucleus with chromatin
Equator of the cell
Condensed chromosomes
Disappearing nuclear membrane
Poles of the cell
Mother cell
Two daughter
cells
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PROPHASE
chromosomesbecome visible
nuclear envelopedisappears
nucleolusdisappears
http://www.ac-dijon.fr/pedago/svt/documents/mitose/prophase.gif
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Prophase
• Centrioles move to the opposite sides of cell
• Spindle fibers from centrioles connect with chromosomes
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Prophase
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METAPHASE
http://iccbweb.med.harvard.edu/mitchisonlab/Pages/mt.html
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METAPHASE
http://www.chembio.uoguelph.ca/educmat/chm736/cycletx.htm
chromatids
spindle
centriole
Chromosomes line up at the equator of the cell
Each chromatid is attached to a separate spindle fiber by its centromere
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Metaphase
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Nature (408. 423, 2000).
chromatids spindle
centriole
http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html
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ANAPHASE
http://www.univ-orleans.fr/SCIENCES/BIOCHIMIE/MMC/accueil.htm
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Conly Rieder http://www.wadsworth.org/BMS/SCBlinks/WEB_MIT2/HOME.HTM
ANAPHASE
early late
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http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html
ANAPHASE
Chromatids separate and migrate to opposite poles
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Anaphase
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TELOPHASE
Daughter Nucleus
Daughter Nucleus
Spindles dissolve
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Telophase
• Chromosomes uncoil
• Two identical nuclei are formed (DNA is in the chromatin form)
• Nuclear membrane & nucleolus reappear
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Cytoplasmic Division: Cytokinesis
• Division of a cell’s cytoplasm to form two identical cells
• Usually begins in late anaphase• Interphase begins when cytokinesis is
complete
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Replication
Chromosomes, Chromatids & Centromeres
Centromere
Chromosome arm
Chromosome arm
Identical chromatid(sister chromatid)
Chromatid
Anaphase
A packaged chromosome
Two identical chromosomes
DNA doubling during S-phase
Joins sister chromatids
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Results of Mitosis:
Two new diploid cells with chromosomes that are identical to those of the parent cell
Hmm…
Why is it necessary for a cell’s chromosomes to be distributed to its daughter cells in such a
precise manner?