Transcript Cellular Reproduction - Gainesville Independent School

Chromosomes and Cellular
Reproduction
Chapter 6
Prokaryotic Cell Reproduction
•Prokaryotes reproduce via Binary Fission, occurs in two stages:
1.
DNA is replicated and prokaryote adds a new cell membrane
between the two copies (FtsZ ring).
•
"Filamenting temperature-sensitive mutant Z”
Prokaryotic Cell Reproduction
•Prokaryotes reproduce via Binary Fission, occurs in two stages:
1.
DNA is replicated and prokaryote adds a new cell membrane
between the two copies (FtsZ ring).
•
2.
"Filamenting temperature-sensitive mutant Z”
FtsZ ring pinches cell into two independent identical cells.
Eukaryotic Cell Reproduction
• Large amounts of
information are
encoded in DNA, and
they are organized into
individual units called
genes.
• A gene is a segment of
DNA that codes for a
protein or RNA
molecule (Traits).
•
Eukaryotic Cell Reproduction
HeLa cells stained for DNA with the Blue Hoechst dye. The
central and rightmost cell are in interphase, thus their entire
nuclei are labeled. On the left a cell is going through mitosis
and its DNA has condensed ready for division.
• As the eukaryotic cell
prepares to divide, the
chromosomes-(the DNA
and its associated
proteins)-become
visible, a process called
DNA condensation
• Before this happens,
however, the DNA has
already been copied.
Eukaryotic Cell Reproduction
• DNA condensation
– The linear DNA strand
“super coils” around
histone proteins.
– Exact copies are called
chromatids, which are
attached at the
centromere.
1. First Growth Phase (G₁-Gap Phase)
• A cell grows rapidly, and
carries out routine
functions. Cells that are
not dividing or in the
process of remain in
this phase
2. Synthesis Phase (S phase)
• The cells DNA is Copied,
at the end of this phase,
each chromosome
consists of two sister
chromatids joined
together at the
centromere
3. Second Growth Phase (G₂ phase)
• Preparations are made
for the nucleus to
divide. Microtubules
are rearranged during
this phase in
preparation for mitosis
4. Mitosis
• The Nucleus of the cell
is divided into two
Nuclei, each nucleus
end up with the same
number and kinds of
chromosomes as the
original cell.
5. Cytokinesis
• The cytoplasm divides
and two daughter cells
arise from a single
parent cell.
Control of the Cell Cycle
• Three Major Checkpoints:
– 1. Cell Growth (G₁) checkpoint
• This checkpoint is to determine if conditions are
favorable for a cell to divide (size, health, etc…)
– 2. DNA Synthesis (G₂) checkpoint
• DNA replication is checked by DNA repair enzymes, if
this checkpoint is passed proteins trigger mitosis
– 3. Mitosis Checkpoint
• Triggers the exit from mitosis, signals beginning of the
G₁ phase.
What happens when Control of the
Cell Cycle is Lost?
The Cell Cycle
• A cell spends 90% of its
time in the first three
phases, collectively
called interphase.
• Total, there are 5
phases of the cell cycle
Mitosis and Cytokinesis
Chapter 6
Section 3
1. First Growth Phase (G₁-Gap Phase)
• A cell grows rapidly, and
carries out routine
functions. Cells that are
not dividing or in the
process of remain in
this phase
2. Synthesis Phase (S phase)
• The cells DNA is Copied,
at the end of this phase,
each chromosome
consists of two sister
chromatids joined
together at the
centromere
3. Second Growth Phase (G₂ phase)
• Preparations are made
for the nucleus to
divide. Microtubules
are rearranged during
this phase in
preparation for mitosis
4. Mitosis
• The Nucleus of the cell
is divided into two
Nuclei, each nucleus
end up with the same
number and kinds of
chromosomes as the
original cell.
5. Cytokinesis
• The cytoplasm divides
and two daughter cells
arise from a single
parent cell.
4. Mitosis
• The Nucleus of the cell
is divided into two
Nuclei, each nucleus
end up with the same
number and kinds of
chromosomes as the
original cell.
Forming the Spindle
• Spindles are structures
made up of both
centrioles and
microtubule fibers.
– Involved in moving
chromosomes during cell
division
– The Centrosome is a
organelle that organizes
the assembly of the
spindle.
• Two centrioles in each
centrosome.
The Centriole
• Each spindle fiber is made
of an individual
microtubule
• Each centriole is made up
of nine triplets of
microtubules arranged in
a circle.
• Unlike animal cells, plant
cells do not have
centrioles, but they do
form a spindle that is
almost identical to that
of animal cells.
Separation of Chromatids by Attaching
Spindle Fibers
• Two sets of microtubules
attach on each side of the
centromere and extend
towards opposite poles.
• Once attached to the
centrosome apparatus,
the chromatids will move
along the fibers to
opposite ends of the cell.
• As soon as the chromatids
separate from one
another they are called
chromosomes.
Phases of Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Prophase
• Chromosomes coil up
and become visible
(condensation)
• Nuclear envelope
dissolves
• Spindle fibers form
Metaphase
• Chromosomes move to
center of the cell.
• Line up along the
equator.
• Spindle fibers link the
chromatids to opposite
poles.
Anaphase
• Centromeres divide
during anaphase.
• The two chromosomes
move toward opposite
poles as the spindle
fibers attached shorten
Telophase
• A nuclear envelope
forms around the
chromosomes at each
pole.
• Chromosomes now at
opposite poles uncoil
and the spindle
dissolves.
• Mitosis is complete
5. Cytokinesis
• The cytoplasm divides
and two daughter cells
arise from a single
parent cell.
Cytokinesis
Animal Cells
• Cytoplasm is divided in half,
cell membrane grows to
enclose each cell.
• Cell is pinched in half by
belts of proteins
(microfilaments) called a
cleavage furrow.
• Forms two identical cells.
Plant Cells
• Vesicles formed by the Golgi
Apparatus fuse at the
midline and form a cell
plate.
– Cell plate is a membrane
bound cell wall that forms
across middle of plant cell.
• A new cell wall then forms
on each side of the cell
plate, forming two new
cells.
Cytokinesis