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Sutrishna
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- Biology
- Cellular Biology
- Genetics
- Molecular Biology
- Biotechnology
Currently I'm persuing M.sc in Neuroscience. I teach biology at primary level, secondary level and higher secondary level in West Bengal.
- Biology
- Cellular Biology
- Genetics
- Molecular Biology
- Biotechnology
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About Sutrishna
I'm Sutrishna Samanta, currently persuing Msc in Neuroscience from Calcutta University. I've done my graduation in Biochemistry. I love biological science, sci-fi theory, poetry. Story and poem writing is my hobby. According to me , Biology isn't only a subject it's also our real life life's present .
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Cell
First we need to know what is cell and where it belongs. Actually cell is the unit Body, unit of life. All living organisms have cell.Main constitutes of cell , protein, carbohydrates,lipid, nucleic acids and water.
There are two types of cell- prokaryotic cell and eukaryotic cell
Higher organisms have eukaryotic cell . Eg- Human.
Just think , few years back we all were baby then, but today we became adult. How it is happen? Have you ever question yourself about it?
Okay, actually this because of cell division.
Because of cell division we grow, we heal our wound, we reproduce. And we all are human still we are different from each other because of cell division.
There are two types of cell division in eukaryotic organisms.
1.Karyokinesis 2. Cytokinesis
Karyokinesis means the division of neucleus of cell.
There are also two type karyokinesis cell division- 1. Mitosis 2.Meiosis
And the cytokinesis means the division of Cytokinine of cell.
Cytokinesis completes the cell division.
Mitosis is a process where a single cell divides into two identical daughter cell. The major purpose of mitosis is for growth and to replace worn out cells. Mitosis have some phases- Prophase, Metaphase , Anaphase.
Meiosis is a process where a cell divides twice to produce four daughter cells containing half the original amount of genetic information. These cells are our reproductive cell- sperms in male and eggs in female.Meiosis can be divided into nine stages.Theseare divided between the first time the celldivides (meiosis I) and the second time itdivides (meiosis II):
Meiosis I:
1. Interphase:
The DNA in the cell is copied resulting in two identical full sets of chromosomes.
Outside of the nucleus? are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division?.
During interphase, microtubules extend from these centrosomes.
2. Prophase I:
The copied chromosomes condense into X-shaped structures that can be easily seen under a microscope.
Each chromosome is composed of two sister chromatids containing identical genetic information.
The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on.
The pairs of chromosomes may then exchange bits of DNA in a process called recombination or crossing over.
At the end of Prophase I the membrane around the nucleus in the cell dissolves away, releasing the chromosomes.
The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles.
3. Metaphase I:
The chromosome pairs line up next to each other along the centre (equator) of the cell.
The centrioles are now at opposites poles of the cell with the meiotic spindles extending from them.
The meiotic spindle fibres attach to one chromosome of each pair.
4. Anaphase I:
The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole.
In meiosis I the sister chromatids stay together. This is different to what happens in mitosis and meiosis II.
5. Telophase I and cytokinesis:
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new nuclei.
The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
Meiosis II
6. Prophase II:
Now there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids).In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be easily seen under a microscope.
The membrane around the nucleus in each daughter cell dissolves away releasing the chromosomes.
The centrioles duplicate.
The meiotic spindle forms again.
7. Metaphase II:
In each of the two daughter cells the chromosomes (pair of sister chromatids) line up end-to-end along the equator of the cell.
The centrioles are now at opposites poles in each of the daughter cells.
Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids.
8. Anaphase II:
The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle.
The separated chromatids are now individual chromosomes.
9. Telophase II and cytokinesis:
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new cell nuclei.
This is the last phase of meiosis, however cell division is not complete without another round of cytokinesis.
Once cytokinesis is complete there are four granddaughter cells, each with half a set of chromosomes (haploid):
in males, these four cells are all sperm cells
in females, one of the cells is an egg cell while the other three are polar bodies (small cells that do not develop into eggs).
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