Unit II
Reproduction
Chapter 14 & 15
Cell Division (Mitosis)
“All cells from cells.” Rudolf Virchow (1855)
–
in unicellular
–
–
reproduction for the entire organism
in multicellular –
–
growth and development from the fertilized
egg
replacement of damaged or dead cells
P
Cell division is the complex process of
reliably passing along the genome from
one generation to the next.
P
Cell division involves:
–
1.precise replication of DNA
–
2.the allocation of DNA to opposite ends
of the cells
–
3.the separation of two identical daughter
cells.
Chromosomes
Chromosomes con’t
threadlike
P composed of protein and DNA
P duplicated in advance of division
P all somatic cells have the same number
of chromosomes in their nuclei.
P
P
Cytokinesis
–
P
cytoplasmic division resulting in two
daughter cells
Mitosis (Mitos=thread)
–
results in two genetically identical cells
equivalent to the parent cell
The Human Life Cycle
Cell Cycle
P
alternates between:
–
–
M phase (dividing phase) and
Interphase (non dividing phase)
M Phase
cell divides
P Consists of:
P
–
–
Mitosis -division of the nucleus
Cytokinesis - Division of the cytoplasm
-duration varies depending on the type of cell
(eg 1 - 24 hours)
-nerve cells and muscle cells rarely divide
Interphase
non dividing phase
P about 90% of the cell cycle
P includes the cell’s growth and
metabolic activities
P cell grows and copies its chromosomes
in preparation for division
P
Interphase con’t
P
Consists of three periods:
–
–
–
1.G1 phase -first growth phase
2.S phase -synthesis phase when DNA is
synthesized as chromosomes are duplicated
3.G2 phase-second growth phase
The Stages of Mitosis
5 stages:
P 1.prophase
P 2.Prometaphase*
P 3.metaphase
P 4.anaphase
P 5.telophase
P
P
http://www.youtube.com/watch?v=VlN7K1-9QB0
1.Prophase
P
Each chromosome
is already
replicated and
composed of two
sister chromatids
joined at the
centromere
Prophase con’t
nucleoli disappear
P chromatin becomes discrete chromosomes
P mitotic spindle forms between the
centrosomes
P centrosomes move apart
P
2.Prometaphase (late Prophase)
P
nuclear envelope fragments
P
spindle fibers extend from the poles
towards the equator
P
kinetochores form at the centromere
region
3.Metaphase
P
centrosomes are at opposite ends
P
chromosomes line up at the metaphase
plate
P
kinetochore fibers of sister
chromatids face opposite poles
4.Anaphase
begins when paired centromeres move
apart
P sister chromatids separate and move
to opposite ends
P kinetochore microtubules shorten
P cell elongates
P
5.Telophase
nonkinetochore microtubules further
elongate the cell
P daughter nuclei begin to form at the
poles
P nuclear envelope begins to form
P nucleoli reappear
P chromosomes become less distinct
P
http://www.youtube.com/watch?v=BFWelOJ7fW0&feature=related