B. S phase
2.3 INVESTIGATING i. DNA replication occurs
ii. Synthesis of histone proteins takes place
THE IMPORTANCE OF iii. DNA wind around histone beads and form
chromatin.
CELL CYCLE AND CELL C. G2 phase
DIVISION
i. Cells continue to grow through protein
synthesis as well as cellular organelles.
ii. Proteins essential for mitotic phase will be
2.3.1 The cell cycle synthesized.
The sequence of events that takes place in the cell iii. Duplication of centrosomes takes place.
from the end of one cell division to the end of the
next cell division is referred to as cell cycle.
At the end of the cell division, two genetically
Cell cycle controlling checkpoints
identical daughter cells resembling the parent cell There are cell cycle-controlling checkpoints
are produced in mitosis. available at G1, G2 and M phase
This to ensure that the cell is ready for moving
into upcoming phases of cell division.
If a cell receives a go-head signal at the G1
check point, it will usually complete the G1, S, G2
and M phases and divide.
If it does not receive a go head signal at that
point it may exit the cycle and enter a non-
dividing stage called the Go phase.
Most cells of the human body are in the Go
phase.
E.g.: nerve cells and muscle cells.
2.3.2 Mitosis
Mitosis is the nuclear division which gives rise
At the end of the cell division, two genetically to two genetically identical daughter nuclei
identical daughter cells resembling the parent cell from a mother nucleus.
are produced in mitosis. This may get divided into five stages in order to
ease the learning of activities of cell cycle:
1. Prophase
EUKARYOTIC CELL CYCLE 2. Prometaphase
Eukaryotic cell cycle has two major phases: 3. Metaphase
1. Interphase: 4. Anaphase
It covers about 90% of the cell cycle 5. Telophase
Is the longer phase of cell division.
2. Mitotic phase/ M-phase
Covers only about 10% of cell cycle.
This includes mitosis and cytokinesis.
INTERPHASE
Interphase could be divided into three phases
1. G1 phase (first gap phase)
2. S phase (synthetic phase)
3. G2 phase (second gap phase)
A. G1 phase
i. Synthesis of proteins
ii. Cell growth by the production of cellular
organelles
iii. Proteins essential for S phase are produced
, 1. Prophase 3. Metaphase
Chromatin fibers get condensed by shortening and Centrosomes reach the opposite poles.
thickening and transformed into chromosomes. The chromosomes have arrived at a place called
Chromosomes appear with two sister chromatids metaphase plate which is located in equal distance
attached at the centromere. from each pole.
(Chromosomal arms) sister chromatids are The centromeres of all chromosomes are located in the
attached by special proteins called cohesin. metaphase plate.
As a result, chromosomes will be visible through At the end of this phase, each chromosome has
light microscope. attached to the ‘kinetochore microtubule’ at their
Nucleoli Disappears centromere and are aligned at the metaphase plate.
The formation of mitotic spindles begins.
(Spindle is formed by accumulated microtubule
complex which includes the centrosomes, the
spindle microtubules and the aster)
Centrosomes move toward opposite poles of the
cell due to the lengthening of microtubules
between them.
4. Anaphase
Sister chromatids are separated at the centromere.
Microtubules attached to kinetochore get shorten and
pull sister chromatids towards the opposite poles.
Cell elongates as the ‘non-kinetochore microtubules’
are lengthened.
By the end of anaphase, equal and complete set of
chromosomes found at each pole of the cell.
2. Prometaphase
The nuclear envelope fragments.
Chromosomes get even more condensed.
Special protein called kinetochore attaches the
sister chromatids of each chromosome at their
centromere.
Some microtubules will attach to the kinetochore
of the chromosomes and move them back and
5. Telophase
forth. Nuclear envelope reforms around each set of
Microtubules which are not attached to the chromosomes at opposite poles.
kinetochore interact with those from the opposite Nucleoli reappears.
poles Spindle microtubules get depolymerized.
Chromosomes unwind and become less condense to
form chromatin.
Two genetically identical daughter nuclei are formed.
Telophase and cytokinesis
2.3 INVESTIGATING i. DNA replication occurs
ii. Synthesis of histone proteins takes place
THE IMPORTANCE OF iii. DNA wind around histone beads and form
chromatin.
CELL CYCLE AND CELL C. G2 phase
DIVISION
i. Cells continue to grow through protein
synthesis as well as cellular organelles.
ii. Proteins essential for mitotic phase will be
2.3.1 The cell cycle synthesized.
The sequence of events that takes place in the cell iii. Duplication of centrosomes takes place.
from the end of one cell division to the end of the
next cell division is referred to as cell cycle.
At the end of the cell division, two genetically
Cell cycle controlling checkpoints
identical daughter cells resembling the parent cell There are cell cycle-controlling checkpoints
are produced in mitosis. available at G1, G2 and M phase
This to ensure that the cell is ready for moving
into upcoming phases of cell division.
If a cell receives a go-head signal at the G1
check point, it will usually complete the G1, S, G2
and M phases and divide.
If it does not receive a go head signal at that
point it may exit the cycle and enter a non-
dividing stage called the Go phase.
Most cells of the human body are in the Go
phase.
E.g.: nerve cells and muscle cells.
2.3.2 Mitosis
Mitosis is the nuclear division which gives rise
At the end of the cell division, two genetically to two genetically identical daughter nuclei
identical daughter cells resembling the parent cell from a mother nucleus.
are produced in mitosis. This may get divided into five stages in order to
ease the learning of activities of cell cycle:
1. Prophase
EUKARYOTIC CELL CYCLE 2. Prometaphase
Eukaryotic cell cycle has two major phases: 3. Metaphase
1. Interphase: 4. Anaphase
It covers about 90% of the cell cycle 5. Telophase
Is the longer phase of cell division.
2. Mitotic phase/ M-phase
Covers only about 10% of cell cycle.
This includes mitosis and cytokinesis.
INTERPHASE
Interphase could be divided into three phases
1. G1 phase (first gap phase)
2. S phase (synthetic phase)
3. G2 phase (second gap phase)
A. G1 phase
i. Synthesis of proteins
ii. Cell growth by the production of cellular
organelles
iii. Proteins essential for S phase are produced
, 1. Prophase 3. Metaphase
Chromatin fibers get condensed by shortening and Centrosomes reach the opposite poles.
thickening and transformed into chromosomes. The chromosomes have arrived at a place called
Chromosomes appear with two sister chromatids metaphase plate which is located in equal distance
attached at the centromere. from each pole.
(Chromosomal arms) sister chromatids are The centromeres of all chromosomes are located in the
attached by special proteins called cohesin. metaphase plate.
As a result, chromosomes will be visible through At the end of this phase, each chromosome has
light microscope. attached to the ‘kinetochore microtubule’ at their
Nucleoli Disappears centromere and are aligned at the metaphase plate.
The formation of mitotic spindles begins.
(Spindle is formed by accumulated microtubule
complex which includes the centrosomes, the
spindle microtubules and the aster)
Centrosomes move toward opposite poles of the
cell due to the lengthening of microtubules
between them.
4. Anaphase
Sister chromatids are separated at the centromere.
Microtubules attached to kinetochore get shorten and
pull sister chromatids towards the opposite poles.
Cell elongates as the ‘non-kinetochore microtubules’
are lengthened.
By the end of anaphase, equal and complete set of
chromosomes found at each pole of the cell.
2. Prometaphase
The nuclear envelope fragments.
Chromosomes get even more condensed.
Special protein called kinetochore attaches the
sister chromatids of each chromosome at their
centromere.
Some microtubules will attach to the kinetochore
of the chromosomes and move them back and
5. Telophase
forth. Nuclear envelope reforms around each set of
Microtubules which are not attached to the chromosomes at opposite poles.
kinetochore interact with those from the opposite Nucleoli reappears.
poles Spindle microtubules get depolymerized.
Chromosomes unwind and become less condense to
form chromatin.
Two genetically identical daughter nuclei are formed.
Telophase and cytokinesis
