The Cell: Mitosis

The Cell: Mitosis

In a previous article, I began discussing the cell. I gave a brief overview of cellular function along with some of the internal components of the cell. In a second article, I discussed the uniqueness of the prokaryotic cell. In this article, we will be discussing one of the most important functions of the cell. Mitosis is essentially cellular duplication.  This article will discuss the parts of mitosis as well as the implications of the process in the origins debate.

Mitosis is a step by step process. Different creatures have different methods of mitosis, and only eukaryotic cells perform mitosis. Prokaryotic cells do not undergo mitosis, instead reproducing by binary fission. Mitosis has six stages, seven in plant cells. They are, in order, Interphase, Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. This article will break down each phase, discussing what happens in each phase.  At the end of the article, I have included a link to a fantastic animation of how mitosis works for anyone who would like to see it.

The first phase of mitosis is known as Interphase. Interphase is by far the longest phase of mitosis because it is the preparation phase. The point of mitosis is to replicate the cell. Thus interphase is used to prepare the cell to replicate.  The cell completely duplicates its DNA during interphase. This results in two, identical strands of DNA, known as chromosomes. At the same time, in the cell cytoplasm, two special structures called centrosomes. During interphase, special structures called microtubules form from the centrosomes. These structures will be important later so keep them in mind as we move into prophase.

Prophase is the second phase of mitosis.  In plants, a special version of prophase, called pre-prophase, takes place before prophase and consists of the nucleus moving to the center of the cell.  However, prophase proper begins after interphase when the chromosomes coil up into visible bundles, though they remain uncondensed.  Each chromosome consists of two identical parts called chromatids. These chromatids attach together at a centrosome.  Also during prophase, a special structure, called a mitotic spindle, forms. The spindle has microtubules attached to it.  The mitotic spindle attaches to the centrosomes by means of these microtubules.  Toward the end of prophase, the nucleolus, which contains the DNA in the nucleus, dissolves, releasing the two paired chromosomes into the nucleus.

Once prophase completes, the cell progresses to the next step, which is known as prometaphase.  Prometaphase is a shorter step than most of the rest of mitosis. The membrane of the nucleus breaks down during prometaphase, allowing the chromosomes to move freely. Guided by the mitotic spindle, the two chromosomes begin to migrate towards the outer edge of the cell.  Specialized microtubules attach to the chromosomes, allowing them to move.  Once they have migrated far enough, another specialized structure called a kinetochore triggers the beginning of metaphase. Without this kinetochore, the cell would skip metaphase and jump into the next phase.

In metaphase, the chromosomes begin to line up along something called the equatorial plane, which is an imaginary line drawn down the middle of the cell.  The centromeres are now found at opposite ends of the cell.  The mitotic spindle is still attached to each one.  Each chromatid is individually attached to the mitotic spindle. That is going to be important later.  Once this is complete, the cell performs a special check to ensure that the process is going appropriately.  If this check passes, the cell will continue the process.

Having passed the check, the cell proceeds into anaphase.  In anaphase, the chromosomes are pulled apart. Until this point, the chromosomes were held together by specialized proteins called cohesins.  However, these are dissolved, and the mitotic spindle pulls the sister chromatids to opposite ends of the cell.  The cell begins to elongate into an oval shape. Towards the end of anaphase, the cell begins the process of cytokinesis. Cytokinesis is the process of cellular division.  This process will continue into telophase.

Telophase is the final stage of mitosis.  In this stage, the separated chromatids reach the opposite ends of the cell.  They bind together with the chromatid from the other chromosomes, and a new nucleus begins to form around each of the newly paired chromosomes.  As the nucleus forms, the chromosomes begin to unwind into their normal, uncoiled state.  At the same time, the mitotic spindle and microtubules begin to disassemble. They will be completely gone by the end of telophase.  Cytokinesis continues as the cell splits into two, identical daughter cells.

If the above process seems a little complicated, that is because it is complicated.  The above explanation is an extremely simplified explanation of how mitosis works.  However, the above should illustrate the level of detail, intricacy, and organization required for mitosis to work. This brings up the inevitable question of how did the mitotic process arise? Could such an intricate, complex process arise through random natural processes? The answer is a resoundingly obvious no.  Every piece, every fragment of the mitotic process has to work together seamlessly in order for the process to work.  The mitotic spindle must form during prophase, for example, or chromosomes will not separate.   If it formed any later, the chromosomes will not separate in time for cytokinesis to complete.  If it formed during interphase, it would have nothing to attach to. This is just one example of how ordered, how designed the process is and must be in order to work.  Mitosis must take place in order for new cells to form and must take place in exactly the order laid out above. The process cries out for a Designer. Evolutionists refuse to accept this, but failing to accept it flies in the face of reality.  Mitosis was designed to work exactly how it does.

The design of mitosis strongly supports a Creationist worldview. A creationist looks at mitosis and sees the mighty, all-powerful, all-knowing hand of God at work. He built the cell, and He put the mitotic process together in the perfect, magnificent manner in which it functions.  No amount of willing away this fact will change it. Mitosis stands as evidence of God’s design in nature and a mighty challenge to evolutionary dogma.

 

 

Mitosis link

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