AAT Bioquest

What are the basic phases of mitosis?

Posted June 10, 2022


Mitosis is the cell division process of eukaryotic cells. It involves 6 basic phases.  Each phase is distinguished by the physical state of the chromosomes and spindle. 

Stage 1: Prophase
In the first phases of mitosis, the cell begins preparation for the division of chromosomes. It does this by breaking down some of the existing structures and creating new ones. The chromosomes, which were duplicated during the preparatory stage become compacted and tightly wound. At the same time, the nuclear envelope breaks down and a mitotic spindle, which is composed of strong proteins known as microtubules, begins forming along the edges of the dividing cell. The mitotic spindle grows in length during this phase, preparing for their role in moving and organizing the chromosomes during mitosis. 

Stage 2: Prometaphase

The abrupt breaking down of the nuclear envelope into many tiny vesicles marks the beginning of the second phase – prometaphase. This is a very dynamic part of the cell cycle. The fragmentation of the nuclear membrane is essential for assembling the mitotic spindle. At the end of this phase, the chromosomes have a bi-orientation. 

Stage 3: Metaphase
Metaphase starts with the lining up of pairs of condensed chromosomes along the equator of the elongated cell. The chromosomes move in a random manner until they align at right angles to the spindle poles at the metaphase plate. During this phase, the checkpoint ensures that the kinetochores are correctly attached to microtubules and that the pairs of chromosomes are evenly divided between the two daughter cells. If there are problems with the alignment or attachment, the cell division is halted and the problem is resolved before proceeding. 

Stage 4: Anaphase

The abrupt separation of sister chromatids marks the beginning of anaphase. The sister chromatids are drawn to the opposite ends of the elongated cell and travel through the spindle mechanism to get to the opposite poles of the cell. Here, the glue that holds them together breaks down and the chromatids move apart towards either side of the cell, ready for complete division. At this stage, each sister chromatid is a full and complete chromosome, and is known as the daughter chromosome. Towards the end of mitosis, the microtubules shorten, triggering the cell separation process. 

Stage 5: Telophase 
During this phase, the mitotic spindle breaks down into its building blocks and the fragmented nuclear envelope rearranges itself to form two new nuclear envelopes at opposite poles – one for each of the two newly created daughter chromosomes.  With the equal division of the genetic contents of one cell into two cells, mitosis is almost complete except for one last step.  

Stage 6: Cytokinesis
Cytokinesis marks the end of mitosis. It is different in animal cells and plant cells because of the presence of a cell wall in plant cells. During cytokinesis animal cells, a band of filaments composed of proteins cleave the elongated cell into two brand new, identical daughter cells.  During cytokinesis in plant cells, the cell is cleaved by a structure called the cell plate that forms down the middle of the cell. In both plant and animal cells, the daughter cells that are generated during mitosis have identical genetic compositions. They are also genetically identical to the parent cell. Each daughter cell also contains its own nucleus as well as a complete copy of the parent cell’s DNA. The cytoplasm from the parent cell is divided equally between the two cells. 

Additional resources

The biochemistry of mitosis

Cell Navigator®CDy6 Mitosis Imaging Kit