Prophase II

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. 

Cell Cycle

There are different cell cycle phases. They differ by organelles present in cells and cells with nuclei land into two steps: 1.) Interphase and 2.) M phase.

Interphases

Interphase is the phase after the M phase that a cell has performed during its previous cell division. Interphase has three stages of cell division in itself; G1, S, and G2 are the three phases. In the interphase, the changes start taking place in the cell. Its size and organelles increase, prepare for DNA replication in other stages, and proceed to mitosis or cytokinesis after the last step.

M (mitotic) phase

This phase is the chromosome division process. In this phase, a cell multiplies and aligns its chromosome to get separated into two cells. Cell partitions its nuclei in two halves. This process is divided into four stages. 1.) Prophase 2.) Meta phase 3.) Anaphase 4.) Telophase.

• Prophase: The nucleolus starts vanishing, and the spindle fibres start developing. Chromosomes start condensation.

• Metaphase: Centromeres reach the layers of cells from inside. Spindle gets fully evolved, and the force to separate the cell from the spindle starts. Both nuclei move towards opposite poles inside a cell.

• Anaphase: The sister chromatids get separated and attach to opposite poles with chromosomes.

• Telophase: The spindle gets separated in this phase.

Prophase 

• Prophase is the first stage of mitosis. 

• The genetic material begins condensation during this stage that continues until the next phase. 

• The condensation of chromosomes is done mainly by a protein known as condensin. 

• This protein helps in the formation of individual sister chromatids. 

• The protein is then restricted to the centromere of the chromosome. 

• Chromosomes of prophase are represented as monovalent (two chromatids attached at the centromere). 

• At the end of the prophase, spindle fibres also begin from polar caps in plant cells and the centrioles in animal cells.

Prophase – II

The chromosomes reappear. The nuclear membrane disappears, and the formation of a spindle starts. Each prophase consists of two distinct chromatids attached to the single centromere.

• Two new daughter cells have half the number of chromosomes, but the amount of DNA is still double.

• The X-shaped structures can be seen under a microscope in each of the two daughter cells.

•  The daughter cell releases its chromosomes once the membrane around its nucleus dissolves.

• Each centriole duplicates itself.

• Once more, the meiotic spindle is formed.

Mitotic Prophase

During prophase, the initiation of condensation of chromosomal material occurs. New DNA molecules are synthesised in tangled form, and the nucleolus disappears during the prophase stage. The said DNA molecules get untangled during the process of chromatin condensation. During the synthesis phase of the interphase, the centrioles are duplicated. These centrioles move towards the opposite poles of the cell during Prophase. Prophase occurs after the gap 2 phase of the interphase; DNA synthesis and replication have already taken place.

Characteristics of Prophase                                         

The characteristic features of the Prophase stage are as follows:

From the prophase diagram, it can be seen that the compact mitotic chromosomes during prophase. Chromosome condensation occurs during the prophase. Two chromatids attached at the centromere can be seen in the prophase diagram in the chromosomes.

Mitotic spindles initiate to get assembled, and thus mitotic spindles are formed. During prophase, movement of the centrosomes occurs. The movement process is powered by the effect of centrosome-associated motor proteins and various other proteinaceous components of the cell cytoplasm and microtubules.

Meiotic Prophase

Meiotic Prophase occurs in two stages: prophase I (the most complex phase since, during this phase, the pairing of homologous chromosomes occurs and the exchange of genetic material occurs) and prophase II (similar to the Mitotic prophase). The prophase diagram shows the different stages involved in Prophase I. The various steps involved in prophase-I are leptotene, zygotene, pachytene, diplotene, and diakinesis.

• Leptotene: Chromosome condensation begins, and it marks the start of the prophase (visible from the prophase diagram)

• Zygotene: Pairing of homologous chromosome

• Pachytene: DNA coiling and DNA condensation that is synapsis process completes, DNA recombination or crossing-over (exchange of chromatid material)

• Diplotene: Homologous chromosomes begin to pull apart in chiasmata

• Diakinesis: Condensed chromosomes attain a maximum condensed state.

Conclusion 

Prophase is the process when cell division begins, and some cell components are broken down. In this process, the chromosomes start to condense, and the nucleolus disappears. After the condensation of chromosomes, a compact structure is formed. This article helps you to understand everything about Prophase.