Eukaryotic cells: structure and function

Eukaryotic Cell vs. Prokaryotic Cell:

There are two types of cells found, that originate from a common ancestor - The prokaryotes and eukaryotes. While Prokaryotes are organisms without a cell nucleus and other membrane-bound organelles and are mostly unicellular, but some exceptions are found. In contrast Eukaryotes have their cells have complex structures by internal membranes and a cytoskeleton. The principal membrane bound structure is the nucleus. All animals, plants, fungi, and protists are eukaryotes. (Diffen, 2013) Prokaryotes were the only form of life on Earth until the more complex eukaryotes evolved from them.

Differences between eukaryotic and prokaryotic cells:

The distinctions between these two types of cells create the differences in organisms Thus the groups of organisms that belong basically to the prokaryotes are non-membranous and in contrast the eukaryotes contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Though this is the basic difference, the presence of mitochondria, chloroplasts, cell wall, and chromosomal DNA found in Eukaryotes distinguish them from the prokaryotes which do not have these features. (Diffen, 2013)

Of cells, and the evolution:

The fundamental unit of life is the cell. It was shown that the cells are of two types, based on whether they contain a nucleus or not. The prokaryotic cells (bacteria) lack a nuclear envelope. That means they are non-membranous and the only other type of cells are the eukaryotic cells that have a nucleus in which the genetic material is separated from the cytoplasm. The genomes of the prokaryotic cells are simple, and these cells have no cytoplasm organelles or a cytoskeleton and these difference making them two branches have similarities that are common to both. In other words both have the same basic molecular mechanisms that created the argument that "all present-day cells are descended from a single primordial ancestor." (Cooper, 2000)

The evolution of the present cell sand the steps that created the replication of cells and the membranes and organelles are important. So how did the cells come into being in a situation when Earth was at the least position for inhabitation by life as we know it? About 10 billion ears ago, the dates are set for evolution of life and the scientists of the previous century in the 1920's that argued that about 3.8 billion years ago in the atmosphere of the Earth some 7 million years ago simple organic molecules could form and spontaneously polymerize into macromolecules and the conditions of the earth being that it had little or no free oxygen, but lots of CO2 and N2. Laboratory experiments in the 1950s proved the spontaneous formation of organic molecules by Stanley Miller, who used the discharge of electric sparks into a mixture of H2, Chapter 4, and NH3, in the presence of water, demonstrated that this energy led to the formation of a variety of organic molecules, including several amino acids. (Cooper, 2000)

While these experiments proved that spontaneous formation of life was possible there was an important aspect that is yet to be proved. To sustain life the molecules must procreate themselves -- in modern day cells these are the nucleic acids and proteins and the nucleic acids are capable of directing their own self-replication. Nucleic acids can serve as templates for their own synthesis as a result of specific base pairing between complementary nucleotides" (Cooper, 2000) In 1980s, when it was discovered in the laboratories of Sid Altman and Tom Cech that RNA is capable of catalyzing a number of chemical reactions, including the polymerization of nucleotides.

The progress of life thus has been based on self-replicating RNA molecules and thus the first cell was formed by the enclosure of self-replicating RNA in a membrane composed of phospholipids and the phospholipids are the basic components of all present-day biological membranes, including the plasma membranes of both prokaryotic and eukaryotic cells. (Cooper, 2000) This important step in evolution has thus caused the entire living organisms to be classified into two major groups, and only these two groups of cells form the entire gamut of life as shown in the below figure: (Gregory, n. d.)

The life root path: Fig 1

Primarily since cells originated in a sea of organic molecules, they were able to obtain food and energy directly from their environment. For procreation an energy management system was necessary and thus a system was created where the cells use adenosine 5-triphosphate -- ATP as their source of metabolic energy "to drive the synthesis of cell constituents and carry out other energy-requiring activities, such as movement," and the ATP is created by the process of glycol sis, photosynthesis, and oxidative metabolism and this enables the cells to replicate themselves and causing further evolution. (Cooper, 2000)

Thus the organisms have evolved from these tow basic structures and the organelles and membranous or non-membranous conditions have created different methods of procreation. The principal difference is being the development of the complex nucleus. Now it is pertinent to look into the components of these cells. The eukaryotes developed from a common prokaryotic ancestor along three lines of descent, giving rise to archaebacteria, eubacteria, and eukaryotes, mitochondria and chloroplasts. (Cooper, 2000) The structure of these organisms therefore has similarities and unique structures.

The Structure and Organelles of Cells:

The Eukaryotic cells have a cytoplasm component and it is the space in the cell between the cell wall and encompassing the plasma, membrane and nucleus. The components of the cytoplasm include organelles filaments, particles, and inclusions it is all covered by cytosol that is composed of water, and many ions and amino acids and nucleotides proteins and glucose. The cytoplasm has three subdivisions of function bound membranous organelles that perform designated processes and distinct activities within the cell, causing complex functions to be performed to continue the life and also replicate the cell when necessary. (Kaye, 1997)

The important distinction is that eukaryotic cells are surrounded by plasma membranes and contain ribosomes. They have a nucleus, a variety of cytoplasmic organelles, and a cytoskeleton. This can be seen in plant cells that also have a cell wall, with chloroplasts. The eukaryotic cells are generally much larger than prokaryotic cells, and are complex with cytoplasmic organelles is what allows eukaryotic cells to function efficiently. They also have Mitochondria, which is used for oxidative metabolism and are thus responsible for generating most of the ATP derived from the breakdown of organic molecules. Eukaryotic cells have the cytoskeleton, a network of protein filaments extending throughout the cytoplasm. (Cooper, 2000)

To achieve the transport of proteins to their correct destinations within the cell a set of cytoplasmic organelles, called the endoplasmic reticulum and the Golgi apparatus, function in sorting and transport of proteins destined for "secretion, incorporation into the plasma membrane, and incorporation into lysosomes. The endoplasmic reticulum is an extensive network of intracellular membranes, extending from the nuclear membrane throughout the cytoplasm." (Cooper, 2000)