Cell Cycle and Cell Division

Introduction

All living organisms possess cells. It is most important structurally, biologically, and functionally. By division of cells, they increase the numbers and form all the structures in the body. There are three essential parts that are present in a cell, namely plasma membrane, cytoplasm, and nucleus. The nucleus is a spherical organelle that is located toward the center of the cytoplasm. It is present in eukaryotic cells containing genetic material and takes part in cell division. The cell cycle involves various stages of cell division. In this tutorial, we will learn about the cell cycle in depth.

Cell Cycle

Cell division is a crucial process of living organisms. By division of cells, they increase the numbers and form all the structures in the body. Cell division plays an important role in the process of reproduction. The cell cycle is the course of events where cells duplicate their genomes and synthesize other components of cells. In this process, two daughter cells are produced. The cell cycle involves two phases: Interphase and M phase. The M phase is commonly known as mitosis.

Mitosis

Another name for mitosis is equational division as it generates genetically identical cells that are look-alike with mother cells. Mitosis division occurs only in diploid cells in animals while in plants it occurs in both haploid and diploid cells. The first division of mitosis is a nuclear division (karyokinesis) followed by cell division (cytokinesis).

The stages of mitosis are described below:

Prophase

• It is the first phase of mitosis.

• After S and G2 phases, prophases immediately start. That is marked by the initiation of condensation of genetic material.

• These genetic materials form two closely packed mitotic chromosomes.

• These mitotic chromosomes are constituted of chromatids that affix with the centromere.

• The prophase cycle is completed by beginning the assembly of the mitotic spindle.

• The process is assisted by microtubules and proteinous components that are present in the cytoplasm.

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Metaphase

• The nuclear envelope falls apart during prometaphase.

• Condensation of chromatin into chromosomes is completed.

• In the metaphase, chromosomes constitute two sister chromatids that are attached to centromeres.

• Sister chromatids are identical copies of chromosomes that are formed in the interphase S phase.

• In centromeres, disc-shaped structures are formed that are called kinetochores.

• Kinetochores are made up of protein complexes and act as a site for the attachment of spindle fibers.

• It plays an important role in the movement of chromosomes.

• In this phase all the chromosomes line up in the equator of the cell.

• Supporting fibers and chromosomal fibers are organized in a cell.

• Centromeres are located in the equatorial plane.

• The arms of the chromosomes remain facing towards the pole.

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Anaphase

• In this phase splitting of centromeres takes place.

• The sister chromatids are detached from each other and move towards the opposite poles.

• The centromere of each chromosome leads to the edge while the arms trail behind it

• The spindle fibre becomes short due to depolarization of the tubulin protein. This occurs at the end of the kinetochore.

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Telophase

• The chromosomes have reached their individual poles and start to decondense and lose their individuality.

• After that formation of nuclear envelope takes place.

• The golgi bodies, endoplasmic reticulum and the nucleolus begin to reappear again in telephase.

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Meiosis

In meiosis a single cell divides two times to form haploid daughter cells that are four in number. The cells are gametes. They are known as sperm cells in males and egg cells in females. The meiosis division is divided into two phases and each phase is again subdivided into various stages as listed below:

Meiosis I

Prophase I

• The nuclear envelope breaks apart during prophase I.

• The condensation of chromosomes begins.

  Appearance of spindle fibre.

Prometaphase II

• At the centromere the spindle fibres are linked to the chromosomes.

Metaphase I

• In the equatorial plate the homologous chromosomes line up to make sure that genetic diversity happens among the offspring.

Anaphase I

• In this phase homologous chromosomes are drawn towards poles of the opposite side.

Teleophase I

• Disappearance of spindle fibers occur in this stage.

• Reformation of the nuclear envelope takes place.

Cytokinesis I

• Due to cell division, in the cytoplasm two non-identical haploid cells will be produced.

Meiosis II

Prophase II

• The chromosome condenses into chromosomes.

• Disintegration of the nuclear envelope takes place.

• Migration of centromeres occurs.

• Reformation of spindle fibre takes place in this stage.

Metaphase II

• In equatorial plate the chromosomes line up in this stage.

Anaphase II

• In this phase sister chromatids are drawn towards the opposite poles.

Telophase II

• Disappearance of spindle fibre occurs.

• Redevelopment of nuclear envelope takes place.

Cytokinesis II

• Due to cell division in the cytoplasm four non identical haploid c daughter cells are produced.

Importance and Significance

In living organisms that are present in our environment cell division plays a crucial role.

It is very important for growth and development as well as reproduction. Apart from this it generates new cells from old ones and renews the damaged ones. It also transfers the genetic material from parents to offspring.

Conclusion

All living organisms possess cells. It is most important structurally, biologically, and functionally. By division of cells, they increase the numbers and form all the structures in the body. Cell division is a crucial process of living organisms. The cell cycle is the course of events where cells duplicate their genomes and synthesize other components of cells.

FAQs

Q1. What is a plasma membrane?

Ans: A cell is surrounded by a thin selective membrane which is known as a plasma membrane or cell membrane. Because of selective permeability in nature, it modulates the entry of certain ions and molecules into the cell. Cell membrane is present in both plant and animal cells.

Q2. What do you understand by interphase?

Ans: The phase between two mitotic phases is known as interphase. It is the most active phase of the cell cycle.

Q3. What is a chromosome?

Ans: The nucleus contains chromosomes which are the genetic material. Chromosomes consist of deoxyribonucleic acid. The DNA contains genetic information and instructs the cells accordingly. Chromosomes are organized into chromatin which is further subdivided into euchromatin and heterochromatin.

Q4. What is a nuclear envelope?

Ans: The content of the nucleus is surrounded by a nuclear envelope and separates it from cytoplasm. It also gives structural framework to the nucleus.

Q5. What is cytoplasm?

Ans: The cytoplasm is a semi liquid substance where cell organelles are present. It is located between the plasma membrane and nucleus. The cytoplasm is the site for most of the chemical reactions. The cell organelles like vacuoles, endoplasmic reticulum, mitochondria, and ribosomes are located in the cytoplasm.