Typical Cell as the Fundamental Unit of Life - Term Paper Example

Typical Cell The cell is the fundamental unit of life. There exist millions of different types of cells. Some cells are organisms onto themselves, like bacteria and amoeba cells. Others only function when they are part of a large organism, like the human cells. The cell is the simplest and smallest basic unit of animals and plants. Some organisms are unicellular, that is, consisting of a single cell like the bacteria, while others are multi-cellular, incorporating many cells, like humans (Miller, 2010:23). Each cell operates in a world of its own, taking in nutrients, converting nutrients to energy, performing their functions, and reproducing as necessary. Additionally, each cell keeps its own instructions that enable it to carry out these tasks. The debate over typical cell has been present for several decades. Microbiology scientists in different factions have defined the basic cells with its components, while others argue that the definition of a typical cell is not definite. This paper discusses the basic structure and functioning of the cell to understand whether there is anything like a typical cell. The cell is the fundamental building block for all living organisms. Living cells are divided into two main categories: prokaryotes and eukaryotes. Scientists believe that life on earth began some 4 billion years ago. Prokaryotic cells were the first cells to evolve in the world. These organisms did not have a nuclear membrane, the membrane surrounding the nucleus of a cell. Bacteria cells are an example of prokaryotic organisms. However, the recent discovery of archaea (a second prokaryotic) proves that there was a third life of cellular domain (Panno, 2005:41). Prokaryotes are single cell organisms that do not differentiate or develop to form multi-cellular organisms. Although some bacteria reside as masses of cells or grow in filaments, each single cell is similar to the other and has the capacity to exist independently. The reason behind the existence of the cells is the probability of not separating after cell division, or maybe they remained in a common slime or sheath (Cooper and Hausman, 2009:246). Despite their close arrangement to each other, they do not communicate or interact for continuity. Prokaryotes differ from eukaryotes based on nuclear structure and organization. Prokaryotes have the capability to inhabit everywhere on the planet, including our body surface. Prokaryotes lack the nuclear membrane. They also have no intracellular structure and organelles characteristic of eukaryotes. The functions of the organelles like mitochondria, Golgi apparatus, and chloroplasts are delegated to the prokaryotic plasma membrane. A prokaryote has three main architectural regions: a cytoplasmic part that has the ribosome and cell genomes (deoxyribonucleic acid DNA), a cell envelope that has a plasma membrane, a cell wall, and a capsule, and appendages refered to as pili and flagella (Panno, 2005:67). On the other hand, eukaryotes have a more defined nuclear structure. Examples of eukaryotes include animals, plants, and unicellular organisms. Eukaryotes are approximately ten times larger than prokaryotes, and having up to 1000 times much volume. The major difference between the two is that eukaryotes have compartments within the membrane where particular metabolisms occur (Cooper and Hausman, 2009:290). A significant difference is the nucleus, which is a compartment delineated by the nuclear membrane. The nucleus houses the DNA of the eukaryotic cell, thus the name of the eukaryotes (true nucleus). The eukaryotes also have organelles, special small structures that perform specific functions within a cell. Eukaryotic cells have dozens of different types of these organelles. Eukaryotes were a major development on the life of living things as well as a key evolution concept. Eukaryotes use the same metabolic processes and genetic codes like prokaryotes, but their advanced organizational complexity allows development of multi-cellular organism (Cooper and Hausman, 2009:135). This means that the absence of eukaryotes would mean that fish, birds, mammals, plant, and other complex single-celled organism would not exist. A “typical” cell structure contains several components include a membrane, a cytoskeleton, cytoplasm, genetic material, and organelles. Whether a cell is eukaryotic or prokaryotic, it has a membrane that surrounds the cytoplasm. This is the cell membrane or the plasma membrane. In prokaryotes and plants, a cell wall covers the cell membrane. The purpose of the membrane is to protect and separate the cell from its surrounding. Hydrophilic phosphorus molecules and hydrophobic fat-like molecules make the membrane, giving it the name phospho-lipid bi-layer (Miller, 2010:76). The membrane incorporates various protein molecules that take the role of pumps and channels for moving molecules in and out of the cell. The cell membrane is semi-permeable in that it allows the passage of substances, either partially or fully. The membrane also has receptor proteins that enable the cell to detect external molecules signals like hormones. The cell also has a cytoskeleton that maintains and organizes the shape of the cell. The components assists in anchoring organelles in their right place, and is essential in the process where the cell uptakes materials from the outside (endocytosis). It also is important to the process of cell mobility and growth. The cytoskeleton has numerous proteins, with each controlling the structure of the cell by aligning, bundling, and directing filaments. Another component of the “typical” cell is the cytoplasm. This is the fluid-filled space inside the cell. Prokaryotes have a relatively free-structured cytoplasm without compartments. In eukaryotes, the fluid-compartment is the residence of the organelles and home of cytoskeleton. The cytoplasm has dissolved nutrients that tenable the cell to move materials around the cell and break down waste products, a process referred to as cytoplasmic streaming. The shape of the cytoplasm changes with the movement of the nucleus. The cytoplasm conducts electricity excellently because of the many salts it contains, providing a good environment for cell mechanics. All types of cells also have genetic material content. There are two types of genetic materials: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). The DNA type is the most common in organisms, though others have RNA (Panno, 2005:53). The genetic material of prokaryotes occurs as a circular molecule DNA around the cytoplasm nucleus region. In eukaryotes, the material occurs in chromosomes, which are linear molecules inside the discrete nucleus. Eukaryotes also have some genetic materials in their organelles like chloroplasts and mitochondria. Then there are the organelles. These organs of the cell perform specialized functions in both eukaryotic and prokaryotic cells. They include the nucleus that houses the chromosomes, as well as synthesis of RNA and replication of DNA (Cooper and Hausman, 2009:468). There is also the protein producing machines called ribosome, the power generators mitochondria and chloroplasts, the endoplasmic reticulum (eukaryotes only), Golgi apparatus (eukaryotes only), peroxisomes and lysosomes (eukaryotes only), vacuoles, and centrosome. Some of the organelles are absent in prokaryotes. Outside the cell wall, there is the capsule, flagella, and the fimbriae (pili). Based on the information above, it is conclusive to state that there is nothing such as a “typical” cell. Even though they posses some outstanding resemblance, all cells vary in function and structure. For instance, a human organism begins to develop when a sperm and an egg combine to make a single cell, which starts to multiply forming a big mass of cells (Cooper and Hausman, 2009:364). As this multi-cellular organism develops and grows, each cell differentiates and specializes in performing certain particular functions. In this regard therefore, all cells are unique in their structure and function. Let us consider a “typical” cell, which is egg-shaped having a nucleus near the centre surrounded by cytoplasm, which then houses other organelles. However, many of the human body cells differ with this “typical” cell structure. The human muscle cell deviates from the shape of the egg-like shape of the cell. Sperm cells also posses a deviant shape, and have extra features like the acrosome (Cooper and Hausman, 2009:425). The human red blood cells do not have a nucleus. Again, nerve cells have a conflicting shape, and an additional layer of myelin for protection. Many human body cells remotely reflect all the descriptions of a “typical” cell. Bibliography Cooper, G., and Hausman, R., 2009. The Cell: A Molecular Approach. Washington DC: ASM Press. Miller, J., 2010. The Cell. New York: Hyperion. Panno, J., 2005. The Cell: Evolution of the First Organism. New York: Facts On File Inc. Read More