Unit 5.1 (Mitosis)

Purpose of Mitosis

Cells can replicate (copy) themselves through a process called Mitosis. Mitosis is a strictly regulated process which allows a multicellular organism to; grow, develop, and heal damage to tissues/organs of their body. Mitosis can be divided into 6 simple steps; Interphase, Prophase, Metaphase, Anaphase, Telophase and Cytokinesis. The steps of mitosis can be remembered with the acronym I.P.M.A.T.C..

Stages of the Cell Cycle

Interphase

During interphase the cell is able to conduct its normal functions and behaviors. Most cells will spend most of their lifespan in interphase. During interphase the genetic material of the cell is loosely packed and unwound to form Chromatin. The DNA is easier to replicate while loosely packed together as chromatin because the DNA replication enzymes have increased access to the DNA strand. During interphase cells will also focus on growing and increasing their size/volume . Cell will also increase their number of organelles like mitochondria, and chloroplast in preparation for cell division.

Prophase

This stage of mitosis is indicated by the nuclear membrane disintegrating and the formation of condensed chromosomes. In animal cells the organelle called centrioles begin producing spindle fibers. The spindle fibers are responsible for eventually pushing and pulling the chromosomes around the cell.

Metaphase

The spindle fibers attach to the chromosomes by the centromeres, the chromosomes are lined up single file down the equator of the cell (metaphase plate). At this stage the nuclear membrane is completely gone.

Anaphase

The spindle fibers push and pull the sister chromatids apart. The sister chromatids separate so that there is only one of each pair towards the poles of the cell.

Telophase

The nuclear membrane begins to reform during telophase. The chromosomes also begin to decondense back to chromatin.

Cytokinesis

Cyto – cell and kinesis- movement combine to create the word Cytokinesis, the movement of the internal components of a cell (cytoplasm) into two new daughter cells. This stage of mitosis is when the cell that has duplicated all of its internal components will not split and form two new daughter cells.

Cytokinesis is slightly different in plant vs animal cells. In animal cells the cells will pinch off and form an area called the cleavage furrow. Eventually the cleavage furrow will pinch off and allow cytokinesis to occur forming two separate daughter cells.

In plant cells a cleavage furrow cannot be formed because plant cells are more rigid due to having a cellulose rich cell wall. Instead, the golgi bodies of plant cells form a cell plate which turns into a new section of cell wall. The cell plate forming cell wall allows for cytokinesis to occur in plant cells.

Cancer’s relationship to Mitosis

As stated earlier mitosis is a very strictly regulated process, everything must go well in order to get a daughter cell that is identical to the original cell. If something goes wrong there are natural systems and mechanisms that the cell can use to identify these errors and fix their mistake. But, occasionally these errors get by. Repeated unchecked errors in DNA replication result in an accumulation of mutations for a cell. If those mutations are occurring in segments of DNA responsible for controlling the process of mitosis, then the cell may replicate uncontrollably.

This uncontrolled cell division/replication is a hallmark of the disease known as “Cancer”. According to the Centers for Disease Control (CDC), in 2019 almost 1.8 million new cases of cancer were diagnosed and about 600,000 people died of cancer. Many people have a loved one or friend that has been effected by cancer so it is important for everyone to have a basic understanding of this disease.

The accumulation of mutations could be caused by external/environmental factors such as; exposure to mutagens, poor diet, lack of exercise, increased exposure to UV-rays, and even stress.