Cells are the building blocks of life that house the most important functions of any living organism.
Cell division allows an organism to grow, regenerate and heal. Cells have limited lifespan and are constantly regenerating.
There are various processes that facilitate the division and multiplication of cells.
The process used will depend on the type of organism and the cells that are being divided.
Two of these division processes are called cytokinesis and mitosis. But what are these processes? What is the difference between cytokinesis and mitosis?
If you want to learn more about cell division, how it works, and the different types of cell division then you are in the right place.
We have put together this interesting and informative guide to tell you everything that you need to know. Keep reading to find out more.
What Is Cell Division?
Cell division is the process by which cells multiply.
The cytoplasm and nuclear material need to be split between the original cell and the new cell that is formed.
Cell division is very important for single celled organisms and multicellular organisms to create more of a particular type of cell.
For a single celled organism it can quickly expand the population.
There are different types of cell division including binary fission, meiosis, mitosis. Binary fission is the cell division process used by prokaryotic organisms.
Prokaryotic cells lack internal membranes, which means that they have no definitive nucleus.
Prokaryotes tend to be single celled organisms such as bacteria.
We are going to be concentrating on mitosis which applies to eukaryotic organisms.
Eukaryotic cells have a nuclear membrane which separates them from the rest of the cell.
This means that the process to divide the cell must be different to prokaryotic cell division, as the nucleus and cytoplasmic matter must be divided equally between the two daughter cells.
We will look at the differences between mitosis and cytokinesis and what their functions are in the process of cell division and multiplication. .
The Eukaryotic Cell Cycle
Eukaryotic cells go through a cycle which makes up their entire life span.
The first stage is Interphase which makes up the majority of the lifespan of the cell.
During interphase, the cell is growing and replicating chromosomes in a process called synthesis to prepare for division.
After interphase, the cell moves onto the next stage of the lifespan. This is Mitosis.
What Is Mitosis?
Mitosis is when the nucleus of the cell is divided into daughter cells. This is made up of five different stages.
During prophase, the nuclear membrane dissolves into the cell and the nucleus itself is compressed. Condensin is a material that is used as part of this process.
This is when the chromosomes migrate towards the center of the cell.
The chromatids line up on either side of the metaphase plate.
Chromatids form in sister pairs, and they spread themselves out on opposite sides of the plate ready for when the cell splits.
The chromatids pairs split from each other as they are pulled to the opposite poles of the cell by the spindle fibers.
The daughter nuclei that have newly formed develop a nuclear membrane.
The process of the nuclei dividing is called karyokinesis. The chromatids are still unpaired.
What Happens When Mitosis Goes Wrong?
Not all biological processes always go smoothly. When mitosis goes wrong, it is usually because of an issue during metaphase.
If the sister chromatids do not align correctly along the cell equator, then they will not be split equally between the two daughter cells when the original cell separates.
So what does this mean?
If the sister chromatids are split unequally between the two daughter cells, this means that there will be one cell with too many chromosomes and one cell with too few chromosomes.
This can lead to cell death, a form of organic disease within the organism, or it can even lead to cancer.
The cell with too few chromosomes will not have all of the DNA required to synthesize more chromosomes, which means it won’t be able to divide to form more daughter cells.
This causes the cell to die.
The cell with too many chromosomes will cause an exaggerated expression of the genes contained in those particular chromosomes.
If those chromosomes contain the genes for an inherited disease such as Down’s Syndrome, this will cause the disease to be more prominent in the affected organism.
If the genes of that chromosome happen to promote slow growth of cells then the cell will die and regeneration of that area of the body will be hindered.
If the genes promote fast growth, the cell will divide rapidly and uncontrollably. and this trend will continue, which can cause cancer.
What Is Cytokinesis
Cytokinesis happens after telophase, but technically the end of mitosis and the start of cytokinesis overlap.
Cytokinesis is when the cells start to pinch inwards and then separate.
This cannot happen until the chromatids are at opposite poles of the cell to ensure that there is an equal amount in each of the new daughter cells that is created.
As the new nuclear membranes are formed, the cell splits in two.
Why Is Cytokinesis So Important?
Cytokinesis is a very important part of cell division.
After karyokinesis and the completion of mitosis, the contents of the cell will be positioned ready to split and there will be two nuclei.
However, there is still only one cell. It is the process of cytokinesis which splits the cell into so that there is an equal amount of cytoplasmic components in each daughter cell.
Without the process of cytokinesis you would end up with a multinucleate cell – the nuclei will continue to divide without splitting into new cells. This can occur in striated muscle tissue.
The Role Of Spindle Fibers
The mitotic spindle is formed in prophase from microtubule proteins which are created by centrioles.
During prometaphase, the spindle fibers help the chromatids to migrate towards the center of the cell ready to be lined up.
During anaphase, the spindle fibers cause the chromosomes to separate.
The separation point is called the cleavage furrow, and this is where the cytoplasm begins to divide.
Whilst this is what happens in animal cells, the position of the cleavage furrow in plant cells is thought to be independent of the spindle fibers.
Once the cleavage furrow has formed, the microtubules of the spindle fibers move to the cell cortex inside the cell membrane. This ensures that the nucleus is centered which is important for cell division.
The microtubules that make up spindle fibers also have other important functions in cell division.
They assist with the development of a cytoplasmic diaphragm called phragmosome. Phragmosome is very important when the cell begins to divide.
The microtubules are vital to the preprophase bands that form around the phragmosome which are called medial rings.
These rings are responsible for narrowing the cell in preparation for division.
The Division Of Animal Cells
There are some elements of the cell division process of animals that differ from plant cells.
There is a ring that contracts that makes up part of the cleavage furrow.
This ring is made up of actin and myosin, materials that are also used in the formation of muscles and the process of muscle contraction.
The actin and myosin accumulate at the equator of the cell, influenced by a number of different proteins.
The anillin and spetins proteins help to keep the furrow stable as it forms.
The contracting ring of the cleavage furrow forms a bridge between the two daughter cells before they are completely divided.
But how does this work? The filaments of the ring shorten which causes the ring to ingress, and this force causes the cleavage furrow to form.
The Midibody And Intracellular Vesicles
The midibody is a structure that forms between the two cells at the site of division before the cells separate.
It is made up of the remains of microtubules and spindle fibers. The midibody must be formed before the cell can divide.
Intracellular vesicles are delivered from the golgi bodies to the midbody structure between the two cells.
They help to form the new membrane to make up for the extra surface area as the cell splits into two daughter cells.
Endosomes are recycled to form an endocytic pathway which is important for creating the new membrane.
This process is called abscission. This must happen before cytokinesis can take place and two daughter cells can be formed.
The intracellular vesicles also provide proteins to the site of the cleavage furrow, which are important for the accumulation of actin and myosin and for the stability and localization of the furrow.
The Division Of Plant Cells
Plant cells are different to animal cells in several ways. These differences affect the process of cell division.
Animal cells have a plasma membrane, but plant cells have a cell wall which is thicker and tougher.
This means it will take more than the pinching of the cleavage furrow to separate the cell into two daughter cells.
Cell division of plant cells and the relevant cytoplasm includes cell plate formation.
The cell plate is made out of secretory vesicles. To prepare for cell division, a phragmosome is formed from microtubules.
The phragmosome helps the nucleus to split in two, and then the cell plate is formed within the phragmoplast.
The vesicles in the cell plate make up the plasma membrane which allows for the formation of a new cell membrane on each side of the cell plate.
This means that each daughter cell will have a thick cell wall.
The new cell membrane for each daughter cell joins to the cell membrane of the original cell to form a complete cell membrane for the two new cells.
The vesicles contain lots of different molecules including carbohydrate molecules.
These carbohydrates are used to create a lamella in between the two cell membranes. The cells then release cellulose to create the thick cell wall.
So What Is The Difference Between Mitosis and Cytokinesis?
Both mitosis and cytokinesis form part of the process of cell division.
The two stages of the process overlap, but they are different stages that are important to the overall process.
They each have their own function.
Mitosis is the process by which chromosomes, and therefore sister chromatids, are divided and positioned ready for division.
Cytokinesis is the process by which the cytoplasm and organelles, the cytoplasmic matter, is divided into two separate cells and new cell membranes are formed.
The Function Of Mitosis
Mitosis occurs after interphase, when the cell has grown and replicated enough chromosomes through the process of synthesis to begin division.
There are five stages of mitosis during which the chromatids change and move around the cell to position themselves for division – prophase, prometaphase, metaphase, anaphase, and telophase.
The chromosomes align themselves at the equator of the cell and then split into sister chromatids which are equally divided.
These movements are facilitated by the spindle fibers that are made up of microtubule proteins.
As part of telophase, the nucleus is split into two during a process called karyokinesis.
At the end of mitosis, the chromosomes will have been split equally and correctly positioned ready for the original cell to split into two daughter cells.
These sister chromatids will be pulled to opposite poles of the cell so that a new nuclear membrane can form around each set of chromosomes.
This is when cytokinesis can begin, although there is a slight overlap of mitosis and cytokinesis in real time.
The Function Of Cytokinesis
Cytokinesis is the process that turns the original cell with two nuclei into two daughter cells.
The cell begins to split, forming a cleavage furrow, with equal amounts of cytoplasmic matter on each side.
This will ensure that the daughter cells with each have the same amount of cytoplasm and cell organelles as the original parent cell.
A midibody structure is formed in between the two cells. Molecules such as important proteins are delivered to this site to help create the new cell membrane.
Abscission is the process by which the two membranes are entirely separated, marking the end of cytokinesis.
At the end of cytokinesis, you will have two separate daughter cells that will be at the beginning of their life cycle.
This marks the end of the process of cell division, as the daughter cells will begin interphase. ~They will grow and begin synthesizing chromosomes ready for their own mitosis.
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