To guarantee proper division and production of progeny cells with intact genomes, these activities, namely cell division, DNA replication, and cell development, must be synchronised. The cell cycle of the B cell is when a cell replicates its genome, synthesises other cell parts, and splits into two daughters. While cell proliferation (in terms of cytoplasmic expansion) is continuous, DNA synthesis happens just once during the cell cycle of the B cell. During cell division, a complicated set of activities distribute the replicated chromosomes (DNA) to daughter nuclei. These events are also genetically controlled.
The Cell Cycle’s Phases
Human cells in culture demonstrate a normal cell cycle. These cells divide once every 24 hours on average. The cell cycle length varies from organism to organism. Yeast may complete the cell cycle in less than 90 minutes.
There are two primary stages to the cell cycle of the B cell:
- Interphase
- M Phase (Mitosis phase)
The M Phase is when a cell divides or undergoes mitosis, whereas the interphase is the period between two M phases.It is significant to note that in the 24 hour average duration of cell cycle of a human cell, cell division properly lasts for only about an hour. The interphase lasts more than 95% of the duration of the cell cycle.
The M Phase begins with nuclear division and finishes with cytoplasm division, corresponding to the separation of daughter chromosomes (karyokinesis) (cytokinesis). The interphase, also known as the resting phase, is when the cell prepares for division by going through an organised cell growth and DNA replication process.
The interphase is further broken into three phases:
- G1 phase (Gap 1)
- S phase (Synthesis)
- G2 phase (Gap 2)
The G1 phase is the time between mitosis and the start of DNA replication. The cell is metabolically active and expands continually throughout the G1 phase, but it does not duplicate its DNA. The S phase, also known as the synthesis phase, is when DNA is synthesised or replicated, and the quantity of DNA per cell doubles throughout this time.
If the starting amount of DNA is 2C, it will rise to 4C. The chromosome number does not grow; if the cell has a diploid or 2n number of chromosomes at G1, chromosomes remain the same after the S phase. DNA replication begins in the nucleus during the S phase, while the centriole doubles in the cytoplasm. Proteins are synthesised in preparation for mitosis while the G2 phasSpecifictain cells do not appear to divide (e.g., heart cells).
In contrast, many others divide only when necessary to replace cells lost due to damage or cell death. These cells that do not divide further depart G1 and reach the quiescent stage (G0 ) of the cell cycle of the B cell, which is an inactive state. In this stage, cells are still metabolically active, but they no longer multiply unless the organism requires it.
M PHASE
This is the most dramatic stage of the cell cycle, with nearly all of the cell’s components undergoing considerable reorganisation. It is also known as equational division since the number of chromosomes in the parent and progeny cells is the same. Though mitosis has been separated into four phases of nuclear division (karyokinesis) for convenience, it is critical to remember that cell division is a gradual process with no apparent distinctions between stages. The four phases of karyokinesis are as follows:
- Prophase
- Metaphase
- Anaphase
- Telophase
Prophase
Prophase, the first step of mitotic karyokinesis, occurs after the S and G2 stages of interphase. The new DNA molecules generated in the S and G2 stages are not separate and somewhat interconnected. The onset of chromosomal material condensation characterises prophase. The chromosomal material untangles during the chromatin condensation process. The centrosome, duplicated during the S phase of interphase, now begins to migrate towards the cell’s opposing poles.
Metaphase
The second phase of mitosis begins when the nuclear envelope completely disintegrates, and the chromosomes are distributed throughout the cell’s cytoplasm. Chromosome condensation is complete, and they may be seen clearly under the microscope. This is the stage at which the morphology of chromosomes may be investigated the most readily. The metaphase chromosome comprises two sister chromatids kept together by the centrosome. Kinetochores are tiny disc-shaped structures on the surface of centromeres. These structures serve as attachment points for spindle fibres (which are formed by the spindle fibres) to the chromosomes moved to the cell’s centre.
Anaphase
The two daughter chromatids, now referred to as daughter chromosomes of daughter nuclei, start migrating towards the two opposing poles at the commencement of anaphase. The centromere of each chromosome stays pointed towards the pole and hence at the leading edge as it advances away from the equatorial plane, with the arms of the chromosome following behind.
Telophase
Chromosomes that have reached their respective poles decondense and lose their identity at the start of the final stage of karyokinesis, telophase. Each pair of chromatin material accumulates at each of the two poles, and individual chromosomes can no longer be seen.
Mitosis and Its Importance
Mitosis, also known as equational division, is mainly limited to diploid cells. It is critical to comprehend the significance of this division in an organism’s existence. Are there instances of haploid and diploid insects that you have studied? Mitosis typically produces diploid daughter cells with the same genetic complement as the mother cell. Mitosis is the process through which multicellular organisms grow. The ratio between the nucleus and the cytoplasm is disrupted due to cell expansion. As a result, the cell must divide to restore the nucleo-cytoplasmic ratio. Mitosis makes a substantial contribution to cell repair.
Conclusion
The cell cycle of the B cell refers to the stages that a cell goes through as it progresses from one division. Interphase – a time of preparation for cell division – and Mitosis (M phase) – the actual period of cell division – are the two stages of the cell cycle of the B cell. Interphase is further separated into three stages: G1, S, and G2. The G1 phase is when the cell develops and performs regular metabolism. During this period, the majority of organelle duplication takes place. DNA replication and chromosomal duplication occur during the S phase. The time of cytoplasmic growth is known as the G2 phase. Mitosis comprises four distinct stages: prophase, metaphase, anaphase, and telophase.