B Cell Division

The cell is the smallest unit of life, also considered the structural and functional unit of all living organisms. Cells can be prokaryotic or eukaryotic and are composed of various organelles such as mitochondria, nucleus, plastid, ribosome, and cell membrane. All these organelles perform different functions that are essential to life. When one cell (parent cell) divides into two or more daughter cells, it is called cell division. The daughter cells resulting from the cell cycle grow to form a parent cell and further contribute to cell division. The following paragraphs will cover various topics from cell division to B cell division to mitosis. 

Cell Division

Cell division can be defined as the process by which a daughter cell divides into two or more daughter cells that grow into the parent cell and further contribute to cell division. Cell division can occur in both prokaryotes and eukaryotes. In prokaryotes, it is a simple process that occurs through fission, budding, fragmentation, etc. In eukaryotes, it occurs as a part of the cell cycle. We can observe cell division of two types: mitosis and meiosis. The daughter cells formed after mitosis are exact copies of the parent cell, containing the same genetic information. In meiosis, however, only half the parent cell’s genetic information is carried into the daughter cell. Thus, in meiosis, the daughter cell will not be an exact copy of the parent cell. 

B Cells 

B cells are also known as B lymphocytes. B cells are a type of white blood cell of the lymphocyte subtype. They function as a component of the adaptive immune system, playing a significant role in humoral immunity. In human beings, B cells mostly mature in the bone marrow. They are responsible for mediating antigen-specific immunoglobulin production directed against invasive pathogens. 

B Cell Development 

• Disulphide bonds join two identical heavy and light chains; these make up immunoglobulins.
• A functional heavy chain protein in a large pre-B cell is formed.
• The heavy chain associated with the light chain and the immunoglobulin form the pre-B cell receptor. This is expressed on the cell surface. 
• Quiescent small pre-B cells allow the production of a complete functional B cell receptor with unique specificity.
• The immature B cells encounter Ag, capable of cross-linking their newly expressed B cell receptors. 

B Cell Division

• B cells are generated and divided in the bone marrow. 
• They are generated from haematopoietic stem cells and take one to two weeks to mature.
• Differentiation of B cells is enhanced by the sequence of expression of cell surface receptors and adhesion molecules. These molecules and receptors also allow proliferation at various stages and movement within the bone marrow microenvironment. 
• After that, the immature B cell undergoes further differentiation after leaving the bone marrow.

Regulatory B Cells

• B cells play an important role in priming adaptive CD4+ cells, but they do not play a positive role in priming adaptive CD8+ T cells. 
• They can also dampen T cell-driven immune responses and thus play an important role in giving rise to regulatory B cells.
• Certain B cells with suppressor functions are also known as B10 Bregs. These cells reduce disease severity in animal models. 
• Bregs that secrete IL-10 or transforming growth factor have recently been used in animal models of cancer, autoimmunity, and infection. So, B cells also play an important role in maintaining peripheral tolerance.

Mitosis in Normal Cells

The term “mitosis” refers to the division of the nucleus. It can be used to describe a process of cell division in which both nucleus and cytoplasm are involved. Two daughter cells are formed at the end of mitosis. The daughter cells produced are the exact copy of their parent cell. 

Stages of Mitosis

Mitosis involves four phases or stages: prophase, metaphase, anaphase, and telophase.

Prophase

• Cell division begins, and some cell components are broken down
• The chromosomes start to condense
• The nucleolus disappears
• After the condensation of chromosomes, a compact structure is formed

Metaphase 

• All the chromosomes line up in the middle of the cell
• Two kinetochores of each chromosome are attached to the microtubules from opposite spindle poles

Anaphase

• The sister chromatids move towards opposite poles after separating from each other
• The cell becomes longer owing to the microtubules

Telophase 

• It is the last phase of mitosis in which the cell appears to be divided and starts to re-establish its normal structure

Significance of Mitosis

• It is an important process of division in single-celled organisms
• Mitosis also plays an important role in wound healing and the regeneration of lost parts in plants and animals

Meiosis

Meiosis is a process in which a single parent cell divides to form four daughter cells. The daughter cells produced contain half of the original amount of the parent cell’s genetic material.

Stages of Meiosis 

Prophase I

• It represents the longest phase in the first meiotic division 
• The chromosomes are composed of two sets condensed into an X-shaped formation 
• Pairing up of chromosomes occurs 
• The nuclear membrane dissolves at the end of this stage

Metaphase I

• The chromosomes pair with each other along the centre of the cell
• The chromosomes have a smooth appearance and become more condensed

Anaphase I

• The nature of the chromosome appears to be the same as in mitosis, where a half centromere and one chroma­tid migrates; here, an entire chromo­some with two chromatids and one centromere perform the same behaviour
• The paired chromosomes move to the opposite poles of the cell after being separated by the meiotic spindle

Telophase I and Cytokinesis

• The nuclear membrane starts forming around the chromosomes of two daughter nuclei
• Two daughter cells are produced by the process of cytokinesis

Prophase II

• This phase is similar to prophase I
• The chromosomes are composed of two sets and again condense into an X-shaped formation 
• The meiotic spindle is formed at the end of this phase, and the centrioles duplicate

Metaphase II

• The chromosomes pair with each other along the centre of the cell, as seen in metaphase I
• The chromosomes gain a smooth appearance after becoming more condensed

Anaphase II

• Members of the bivalent chromosome begin to move towards the pole
• With the help of the meiotic spindle, the sister chromatids move towards opposite poles and become individual chromosomes

Telophase II and Cytokinesis 

• Orientation of the chromatid is the only difference from mitosis
• The nuclear membrane forms again
• After cytokinesis, new cells are produced that have a haploid set of chromosomes

Significance of Meiosis

• Meiosis plays an important role in the formation of sex cells or gametes that are responsible for sexual reproduction
• It reduces the number of chromosomes to half, thus playing an important role in maintaining a constant number of chromosomes
• It also plays an important role in introducing the phenomenon of crossing over
• Owing to the irregularities during meiosis, the phenomenon of mutation occurs

Conclusion

The term “mitosis” refers to the division of the nucleus. It can be used to describe a process of cell division in which both nucleus and cytoplasm are involved. Two daughter cells are formed at the end of mitosis. The daughter cells produced are the exact copy of their parent cell. 

Meiosis is a process in which a single parent cell divides to form four daughter cells. The daughter cells produced contain half of the original amount of the parent cell’s genetic material.