Cell Biology - Cell Division Part 2
Mitosis:
It is a second phase of cell cycle and further divided into four phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Prophase:
· It is a beginning phase and condensed chromosomes and nucleolus are observed
· At the end of this phase, condensed chromosomes appears as two chromatids holding together with centromere and nucleolus disappears completely
· Chromosomes migrates towards the nuclear membrane
· If Centrosome is present, two units of it separate and migrate towards opposite poles. Plant cell do not contain Centrosome.
· Centriole located at two different poles develop a bipolar spindle made up of cytoplasmic fibers which is made up of proteins
· Nuclear membrane disintegrate and chromosomes spreads in all over the cell area
Metaphase:
· It is also called as prometaphase
· Centromere of each chromosome migrates and attached to the equatorial plane of the bipolar spindle
· Chromatids float free
Anaphase:
· Centromere of each chromosome holds two chromatids and divides
· Each chromatid has its own centromere and they migrate towards opposite poles due to contraction of spindle fibers
· Chromatid with its independent centromere is known as a chromosome
· At the end of the phase, the number of chromosomes are same as the number of chromosomes occurred in the original cell
Telophase:
· Each chromosomes uncoils and chromatin network appears
· A nucleolus develops on the nucleolar organizer region of a specific chromosome
· At the end, nuclear membrane is reformed and two nuclei exist at two polar region
Cytokinesis:
· It is a process of dividing nuclear region and disappearance of cytoplasmic spindle
· In plant cell, Cytokinesis occurs at the centre of the cell and middle lamella made up of protein is developing from centre towards periphery of the cell. A cell wall is later formed on two sides of middle lamella.
· In animal cell, Cytokinesis occurs by constriction of cytoplasm from peripheral region towards centre of the cell and finally two cells become separated.
Significance of Mitosis:
· The number of chromosomes is same in both the cell
· Cells maintain their cell size
· Degenerated cells are replaced and growth and development occurs
· Single cell develops its multicellular body by forming tissues and organs
Self study:
Example-1: In which of the following cell division, the number of chromosomes remain same as it was in the parent cell?
a) Mitosis
b) Meiosis
c) Interphase
d) Metaphase
Answer: In mitosis type of cell division, the number of chromosomes remains same as it was in the parent cell.
Example-2: In prophase, two Centriole locates at two poles and develops _________________
a. Cytoplasmic fibers
b. Chromatin
c. Bipolar spindle
d. Centrosome
Answer: In prophase, two Centriole locates at two poles and develops bipolar spindle.
Example-3: In which of the following phase, nucleolus develops on the nucleolar organizer region?
a) Metaphase
b) Telophase
c) Prophase
d) Anaphase
Answer: In Telophase, nucleolus develops on the nucleolar organizer region.