The cell is one of the most intricate, detailed, entities to exist on earth. The smallest life form which can duplicate itself without external aid, the cell defies all evolutionary attempts to explain it. Because the cell has such a diverse interior with an extensive number of intra-cellular machines, this series of articles cannot even begin to scratch the surface of the complexity involved. Instead, we will focus on providing a general overview of cellular function in animals in this article. In future articles we will break down the various parts of the cell and discuss how it relates to the origins debate.
The cell is the basic building block of both animals and plants. Every living creature is composed of at least one cell. In animals, the DNA of the organism is found in the nucleus of the cell. The nucleus is characteristic of what are called Eukaryotic cells. Eukaryotic cells make up the vast majority of what we recognize as animal and plant life. Prokaryotic cells are the other type of cell. In this type of cell, the DNA is not found in a nucleus as there is none. Instead it coiled into a structure called a nucleoid. Prokaryotic cells also lack membrane bound organelles which are found in Eukaryotic cells. Organelles are mini-organs found inside the cell. This article will primarily discuss Eukaryotic cells.
Eukaryotic cells are designed to replicate. Replication means duplicating the DNA of the cell. Since the DNA needs to be duplicated, it needs to be kept free of errors. The nucleus keeps the DNA coiled in tight strands, helping prevent damage to the strands and saving space in the cell. However, when the DNA needs to be duplicated, either for the production of a new cell or simply to produce a protein chain, the DNA has to uncoil. When it does so, a complimentary RNA strand is formed. This RNA strand is then sent out of the nucleus into the liquid component of the cell known as the cytoplasm. In the cytoplasm there are tiny organelles called ribosomes. These ribosomes are responsible for constructing protein chains. Ribosomes are found inside another organelle called the endoplasmic reticulum. This ER comes in two forms, one of which completely lacks ribosomes and is thus known as the smooth ER. The ER heavily populated with ribosomes and thus used for protein formation is referred to as rough ER. Some ribosomes float freely in the cytoplasm as well.
The work of a cell does not end once a protein chain has been created. Protein chains are of little use until they are folded. This work is done in a specialized packaging and shipping center called the Golgi Apparatus. The Golgi Apparatus takes the proteins and lipids produced throughout the cell, packages them up, and ships them to either the cell membrane or another location within the cell which needs them.
There are other parts of the cell which have little influence on replication. The mitochondria are the power generators of the cell. They perform respiration, or the conversion of nutrients into usable energy. Cellular respiration is worthy of its own article. For now, simply know that it converts nutrients to energy. The mitochondria are where this process occurs. Vacuoles are storage spaces within the cell. In animal cells they store waste until it can be expelled, much like septic tanks. Lysosomes store digestive enzymes. Worn out organelles, bacteria, and food particles are all fed into Lysosomes. The Lysosomes store the enzymes, keeping them from destroying the cell, and enabling the cell to eat.
Cells undego two types of replication. One kind is called Mitosis. Mitosis essentially creates two new cells which are identical. Each has a single copy of the cells chromosomes. Once the chromosomes have split, the cell divides by cytokinesis. This is how the majority of cellular reproduction takes place. However, in reproductive cells, a different process takes place. This process, known as meiosis, creates four new daughter cells, each of which is haploid. A haploid cell only has one set of chromosomes, rather than the normal two, which is called diploid. Diploid cells are the normal human cells. When reproductive cells from the two genders meet, they fuse into a single diploid cell, containing a single copy of both parents DNA. This is why babies frequently have traits from both their father and mother.
This article has been a mere basic overview of the cell and how it works. I will be discussing the cell in greater detail in future articles. Just bear in mind that, for the purposes of these articles, I have to keep the discussion far simpler than the actual process itself is.