Transcript Asexual Reprodction

Asexual Reproduction
Getting to the Details
Asexual Reproduction in
Prokaryotes
 Binary Fission
 Prior to division, an
exact copy of DNA is
made
 Each copy attaches to
a different point on
plasma membrane
 Cell stretches out and
pinches in two
Asexual Reproduction in
Eukaryotes
 The Cell Cycle or life
cycle of cell can
range from 16 hours
to days, to a lifetime
 Eukaryotic Cells are
more complex, so
process of cell
division is more
complicated
First Stage of Interphase
 G1 - Gap 1 Begins at
the end of cell division
 This is the time for cell
growth and activity
 This stage can be
extended if
environmental factors
are not favorable
Second Stage of Interphase
 S - Synthisis
 The DNA replicates or
makes a copy of itself
during this stage
 Each chromosome
now consists of two
sister chromatids
Third Stage of Interphase
 G2 – Gap 2
 Centrioles replicate,
and begin to separate
 Centriole pairs
produce centrosomes
–spindle organizing
centers
 The nucleolus
produces ribosomes
for increasing protein
synthesis needed for
growth
Mitosis Begins: Prophase
 Changes in the
Nucleus:
 Chromatin condenses
to become visible
 Sister chromatids join
together at centromere
 The Nucleolus
disappears
 Nuclear membrane
begins to dissolve
Prophase Continued:
 Changes in the cytoplasm
 Centrosomes move to
opposite sides to the cell
forming poles
 Mitotic spindles grow out
from the centrosomes
 Each chromosome
attaches to a spindle fiber
microtubule
 Chromosomes begin to
move toward the middle of
the cell
Metaphase
 The mitotic spindle is
complete
 Chromosomes are all
lined up on the
‘metaphase plate’ at the
middle of the cell
 The sister chromatids
face opposite poles.
 Each member of the pair
is attached to a spindle
fiber heading in the
opposite direction
Anaphase
 Anaphase begins when
the two centromeres of
each chromosome come
apart
 The sister chromatids
separate and are pulled
by the spindle fiber to
opposite poles
 Each sister chromatid is
now considered a
complete daughter
chromosome
 The cell begins
elongating
Telophase
 Telophase is roughly
the reverse of
prophase
 Daughter nuclei
appear at opposite
poles as nuclear
membrane forms
around chromosomes
 Chromatin uncoils so
chromosomes no
longer visible
More on Telophase
 Nucleoli reappear
 Mitotic Spindle
disappears
 Cell elongation
continues
 Mitosis is complete
Cytokinesis
 The cytoplasm
divides equally
 In animals, a
cleavage furrow
forms, pinching the
cell in two
 In plants, a cell plate
forms between new
cells, forming a cell
wall
Mistakes in Mitosis
 Cancer occurs when cell cycle regulation
malfunctions
 Cells divide rapidly, forming abnormal
tissue or tumors
 Current research is focusing on cell cycle
regulation
 Most chemotherapies work by disrupting
cell division and the formation of the
spindle fibers