How do cells grow &
reproduce?
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
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
S
Interphase
G2
G1
M
The Cell Life Cycle
Gap 1 - Doubling
of cell size,
increase in the
number of
organelles, regular
cellular activities
S - Synthesis of
DNA
S
G1
G1, S, & G2 =
Interphase =
busy time
G2
M
Gap 2 - Final
preparation for
division
Mitosis - Cell
division
S phase – DNA replication
Fig. 3.26
nucleolus is still
visible
INTERPHASE:
nuclear envelope is
clearly visible
chromatin =
uncoiled DNA
http://www.fed.cuhk.edu.hk/~johnson/photomicrographs/mitosis/animal/animal_interphase.htm
Interphase
•
•
•
•
•
Metabolic phase
Cell growth
DNA replication
Protein synthesis
Visible nucleus with
CHROMATIN
Mother cell
Stages of Mitosis
Nucleus with
chromatin
Interphase
Disappearing
Prophase
nuclear
membrane
Mitotic
spindle
Condensed
Equator
chromosomes
of the cell
Poles of
the cellTwo
daughter
cells
Metaphase
Anaphase
Telophase
PROPHASE
nuclear envelope
disappears
nucleolus
disappears
http://www.ac-dijon.fr/pedago/svt/documents/mitose/prophase.gif
chromosomes
become visible
Prophase
• Centrioles move to the
opposite sides of cell
• Spindle fibers from
centrioles connect with
chromosomes
Prophase
METAPHASE
http://iccbweb.med.harvard.edu/mitchisonlab/Pages/mt.html
METAPHASE
chromatids
Chromosomes
line up at the
equator of the
cell
spindle
centriole
http://www.chembio.uoguelph.ca/educmat/chm736/cycletx.htm
Each chromatid is attached to a separate
spindle fiber by its centromere
Metaphase
chromatids
spindle
centriole
Nature (408. 423, 2000).
http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html
ANAPHASE
http://www.univ-orleans.fr/SCIENCES/BIOCHIMIE/MMC/accueil.htm
ANAPHASE
early
Conly Rieder http://www.wadsworth.org/BMS/SCBlinks/WEB_MIT2/HOME.HTM
late
ANAPHASE
Chromatids separate
and migrate to
opposite poles
http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html
Anaphase
TELOPHASE
Daughter
Nucleus
Spindles dissolve
Daughter
Nucleus
Telophase
• Chromosomes
uncoil
• Two identical
nuclei are formed
(DNA is in the
chromatin form)
• Nuclear membrane
& nucleolus
reappear
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
Chromosomes, Chromatids & Centromeres
A packaged
chromosome
Chromatid
Chromosome
arm
Centromere
Joins sister
chromatids
Chromosome
arm
Replication
DNA
doubling
during Sphase
Identical
chromatid
(sister
chromatid)
Anaphase
Two identical
chromosomes
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?