Cell Cycle and Mitosis

6.2 Cell Cycle and Mitosis
 
Introduction
  • The cell cycle refers to the sequence of events that involves DNA multiplication and cell division to produce two daughter cells.
  • The cell cycle consists of interphase and M phase.
  • Interphase is the longest phase in the cell cycle.
  • This phase is made up of the G1, S and G2 phase.
 
 
Interphase
G1 phase
  • Cells grow.
  • Cell components such as mitochondrion and endoplasmic reticulum are produced at this stage.
  • Proteins used in the cell cycle are also synthesised during this time.
  • At this stage, the nucleus looks big and the chromosome is in the form of chromatin.
S phase
  • DNA synthesis occurs in the S  phase.
  • The DNA in the nucleus is replicated.
  • Each chromosome multiplies into two identical chromosomes known as sister chromatids.
  • Both chromatids contain the same copy of the DNA molecule.
  • Both chromatids are joined at the centromeres.
G2 phase
  • The cells will continue to grow and remain active metabolically during the G2 phase.
  • Cells gather energy and make final arrangements to enter the next stage of cell division.
  • After the interphase stage, the cell will enter the M phase.
 
M phase
  • M phase is made up of mitosis and cytokinesis.
  • Mitosis involves prophase, metaphase, anaphase and telophase.
 

 

Mitosis
 Prophase
  • In the nucleus, chromatin starts to shorten and thicken to form a chromosome structure that can be seen through a light microscope.
  • The chromosome is seen to be made up of two identical threads called sister chromatids.
  • Both sister chromatids are joined at the centromere.
  • The nucleus membrane disintegrates, the nucleolus disappears, the centriole moves to the opposite poles and the spindle fibres start to form.
Metaphase
  • Centrioles are at the opposite poles of the cell.
  • The spindle fibres maintain the chromosomes at the equatorial plane.
  • The chromosomes become aligned in a single row on the equatorial plane.
  • Metaphase ends when the centromere begins to divide.
 Anaphase
  • The centromere divides into two and the sister chromatids separate.
  • Spindle fibres shorten, contract and the sister chromatids are attracted to the opposite pole cells.
  • Anaphase ends when the chromatid arrives at the pole of the cell.
Telophase
  • When the chromatids are at the opposite poles, they are now called the daughter chromosome.
  • Each pole contains one set of complete and identical chromosomes.
  • Chromosomes are shaped again as fine chromatin threads.
  • Nucleoli are formed again.
  • Spindle fibres disappear.
  • A new nucleus membrane is formed.
  • The telophase stage is followed by cytokinesis.
 
 

 

Cytokinesis
  • Cytokinesis is the division of cytoplasm that happens immediately after the nucleus is formed, that is, at the end of telophase.
 
Cytokinesis in Animal Cell
  • Cytokinesis occurs in animal cells when the plasma membrane constricts in the middle of the cell between the two nuclei.
  • Microfilaments at the point of constriction will contract, causing the cell to constrict until it splits to form two daughter cells.
 
 
Cytokinesis in Plant Cell
  • Cytokinesis in plant cells also begins when the formed vesicles combine to form cell plates at the centre of the cell.
  • The cell plates are surrounded by a new plasma membrane and a new cell wall substance is formed among the spaces of the cell plates.
  • The cell plates expand outwards until they combine with the plasma membranes.
  • At the end of cytokinesis, cellulose fibres are produced by the cells to strengthen the new cell walls.
  • Two daughter cells are formed.
  • Each cell has a diploid condition.
 
​​​​
 

 

The Necessity of Mitosis
  • Mitosis is important for the following life processes.
  • For embryo development and organism growth, mitosis ensures that rapid cell growth occurs.
  • Through the mitosis process, the lizard is able to grow a new tail (regeneration) if the tail breaks.
  • When the body is injured, mitosis will produce new cells to replace cells that are dead or damaged.
  • Mitosis aids organisms such as hydra to produce new individuals through the formation of new buds.
  • In agriculture, the technique of culturing plant tissues is used to produce young plants through the culturing of parent cells without going through the fertilisation process.
  • Stem cell therapy uses stem cells from bone marrows to treat damaged cartilage.
  • The culturing technique uses stem cells from animals which are then cultured in laboratories to produce meat.

Cell Cycle and Mitosis

6.2 Cell Cycle and Mitosis
 
Introduction
  • The cell cycle refers to the sequence of events that involves DNA multiplication and cell division to produce two daughter cells.
  • The cell cycle consists of interphase and M phase.
  • Interphase is the longest phase in the cell cycle.
  • This phase is made up of the G1, S and G2 phase.
 
 
Interphase
G1 phase
  • Cells grow.
  • Cell components such as mitochondrion and endoplasmic reticulum are produced at this stage.
  • Proteins used in the cell cycle are also synthesised during this time.
  • At this stage, the nucleus looks big and the chromosome is in the form of chromatin.
S phase
  • DNA synthesis occurs in the S  phase.
  • The DNA in the nucleus is replicated.
  • Each chromosome multiplies into two identical chromosomes known as sister chromatids.
  • Both chromatids contain the same copy of the DNA molecule.
  • Both chromatids are joined at the centromeres.
G2 phase
  • The cells will continue to grow and remain active metabolically during the G2 phase.
  • Cells gather energy and make final arrangements to enter the next stage of cell division.
  • After the interphase stage, the cell will enter the M phase.
 
M phase
  • M phase is made up of mitosis and cytokinesis.
  • Mitosis involves prophase, metaphase, anaphase and telophase.
 

 

Mitosis
 Prophase
  • In the nucleus, chromatin starts to shorten and thicken to form a chromosome structure that can be seen through a light microscope.
  • The chromosome is seen to be made up of two identical threads called sister chromatids.
  • Both sister chromatids are joined at the centromere.
  • The nucleus membrane disintegrates, the nucleolus disappears, the centriole moves to the opposite poles and the spindle fibres start to form.
Metaphase
  • Centrioles are at the opposite poles of the cell.
  • The spindle fibres maintain the chromosomes at the equatorial plane.
  • The chromosomes become aligned in a single row on the equatorial plane.
  • Metaphase ends when the centromere begins to divide.
 Anaphase
  • The centromere divides into two and the sister chromatids separate.
  • Spindle fibres shorten, contract and the sister chromatids are attracted to the opposite pole cells.
  • Anaphase ends when the chromatid arrives at the pole of the cell.
Telophase
  • When the chromatids are at the opposite poles, they are now called the daughter chromosome.
  • Each pole contains one set of complete and identical chromosomes.
  • Chromosomes are shaped again as fine chromatin threads.
  • Nucleoli are formed again.
  • Spindle fibres disappear.
  • A new nucleus membrane is formed.
  • The telophase stage is followed by cytokinesis.
 
 

 

Cytokinesis
  • Cytokinesis is the division of cytoplasm that happens immediately after the nucleus is formed, that is, at the end of telophase.
 
Cytokinesis in Animal Cell
  • Cytokinesis occurs in animal cells when the plasma membrane constricts in the middle of the cell between the two nuclei.
  • Microfilaments at the point of constriction will contract, causing the cell to constrict until it splits to form two daughter cells.
 
 
Cytokinesis in Plant Cell
  • Cytokinesis in plant cells also begins when the formed vesicles combine to form cell plates at the centre of the cell.
  • The cell plates are surrounded by a new plasma membrane and a new cell wall substance is formed among the spaces of the cell plates.
  • The cell plates expand outwards until they combine with the plasma membranes.
  • At the end of cytokinesis, cellulose fibres are produced by the cells to strengthen the new cell walls.
  • Two daughter cells are formed.
  • Each cell has a diploid condition.
 
​​​​
 

 

The Necessity of Mitosis
  • Mitosis is important for the following life processes.
  • For embryo development and organism growth, mitosis ensures that rapid cell growth occurs.
  • Through the mitosis process, the lizard is able to grow a new tail (regeneration) if the tail breaks.
  • When the body is injured, mitosis will produce new cells to replace cells that are dead or damaged.
  • Mitosis aids organisms such as hydra to produce new individuals through the formation of new buds.
  • In agriculture, the technique of culturing plant tissues is used to produce young plants through the culturing of parent cells without going through the fertilisation process.
  • Stem cell therapy uses stem cells from bone marrows to treat damaged cartilage.
  • The culturing technique uses stem cells from animals which are then cultured in laboratories to produce meat.