Based on biological intuition, it is apparent that Eukaryotc cells are more structurally advanced than prokaryotic cells. First, the later cells are single celled and are usually smaller than the former. Eukaryotic cells have true nucleus that is bounded by a membrane, several rod shaped chromosomes and other membrane bound structures such mitochondria. A prokaryotic cell, on the other hand, lacks a defined nucleus, but have a region called nucleoid where a single chromosomal, circular, double stranded DNA molecule is found ( Orchard& Nation, 2014 ). Moreover, it does not enclose other membrane-bound organelles. A eukaryotic cell has various organelles that allow different functions to be compartmentalized in various regions of the cell.
The nucleus is the brain of the cell. Nucleus in an eukaryotic cell is said to be `true` because the cell`s DNA is surrounded by a membrane ( Orchard & Nation, 2014 ). The nucleus directs all the activities in the cell and the production of proteins and ribosomes. In addition, the nucleus is enveloped by a double membrane which constitute of inner and outer membrane. The membranes have pores that allow the exchange of ions, molecules and Ribonucleic acid between cytoplasm and nucleoplasm ( Orchard& Nation, 2014 ). Ribosomes are complex organelles that are responsible for synthesis of protein. They decode the genetic message contained in the genome into protein ( Orchard& Nation, 2014 ). They are made of proteins and RNA in almost equal amount. These organelles are mostly connected to endoplasmic reticulum and a few are scattered in the cytoplasm.
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Mitochondria are other prominent organelles found in eukaryotic cells. They are usually oval shaped, double membrane-bound organelles, which contain their own ribosomes and DNA ( Tager et al., 2009 ). They are responsible for generation of energy that is obtained by respiration of food to produce Adenosine triphosphate; they float freely in the cell. The endoplasmic reticulum(ER) consist of a network of membranous tubules, which form flattened sacks within the cytoplasm and undertake synthesis, folding, modification and transportation of proteins ( Tager et al., 2009 ). Moreover, the organelles are classified into rough and smooth endoplasmic reticulum. The former has rough appearance because it comprise of ribosomes attached to its outer surface. It is also located adjacent to the cell nucleus and its membranes is continuous with the outer membrane of the nuclear covering ( Tager et al., 2009 ). Ribosomes located on the rough ER produces proteins, which have a specified final destination. For instance, they can remain within the ER or directed to Golgi apparatus for transportation
The appearance and functions of the smooth endoplasmic reticulum contrast with those of rough ER. The smooth ER has no ribosomes and its work is to synthesis lipids which include: Cholesterol and phospholipids. These secretions are used in production of new cellular membranes. In certain cell types, smooth ER takes a critical function of producing steroid hormones from cholesterol ( Tager et al., 2009 ). In the liver, these organelles acts in detoxification of drugs and harmful chemicals.
Golgi apparatus are organelles that perform the function of sorting, tagging, packaging and distribution of lipids and proteins ( Tager et al., 2009 ). They are also involved in creation of lysosomes organelles. Lysosome contain digestive enzymes that destroy cells that become worn out, which are then released back into the cell inform of vesicle to be dispelled through the cell membrane. Vacuoles are membrane bound sacs that serve the purpose of storage. Plant cells have additional organelles including: Chloroplast and cell wall. The former captures sunlight and uses it to create food by photosynthesis while the later offers support to the cell.
Organelles are classified into two: Membranous and non-membranous ones. The prime difference between them is that in the former, the organelles are covered by a single or double membranes that are similar to those of cell membrane while in the latter, the organelles are not covered in any kind of membrane ( Orchard & Nation, 2014 ). For that matter, in the former, the content of the organelles are separated from the cytoplasm while in the latter they are continuous within the cytoplasm. Membranous organelles contain fluid filled cavities inside the structures while non-membranous ones do not comprise of any fluid filled cavity inside them ( Orchard & Nation, 2014 ). Additionally, membranous organelles are present only in eukaryotic cells. Non- membranous ones are found in both prokaryotic and eukaryotic cells. Examples of membranous organelles include: Nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, plastids and lysosomes. Some of non-membranous organelles include: ribosomes, nucleoid, centrioles, cilia and flagella.
Cell membrane is a thin semi permeable membrane that surrounds the cytoplasm of a cell. It creates a barrier between the cell and the surrounding environment. The membrane is comprised of four major molecules: Phospholipids, cholesterol, proteins and carbohydrates. The larger percent of the membrane structure is made of phospholipids where a single phospholipid molecule has a head and tail end. The head is hydrophilic and the tail is hydrophobic. The lipids form a bilayer in which the hydrophilic layer face the aqueous cytosol and the hydrophobic part faces the extracellular part fluid ( Michell & Unknown, 2010 ). The lipid layer is semipermeable and it is, therefore, important in allowing only specific molecules to diffuse in the cell. Cholesterol molecules are fairly distributed between phospholipids; they prevent stiffness in the cell membrane by inhibiting phospholipids from being closely stacked together. Glycolipids have carbohydrate sugar and are located on the surface of the cell membrane to help the cell organize other cells of the body ( Michell & Unknown, 2010 ).
The cell membrane proteins are of two types including: Peripheral and integral proteins. The former proteins are found on the exterior and are connected to the membrane by collaboration with other proteins. The latter are implanted into the membrane and most of them pass through the membrane. Cell membrane proteins perform different functions: Structural proteins offer cell support and its shape. Receptor proteins allow the cells to communicate with the external surrounding through the use of hormones, neurotransmitters and signaling molecules ( Michell & Unknown, 2010 ). Transport proteins, for instance, globular ones move the molecules across cell membrane via facilitated diffusion ( Michell & Unknown, 2010 ). Finally, glycoproteins aid in cell communication and transport across the cell membrane.
Apart from the functions performed by the cell membrane`s building structures, the membrane itself has other functions. It protects the integrity of the cell by ensuring that only certain substances diffuse in. Also, it acts as the base of attachment for the cytoskeleton in some organisms ( Alberta et al., 2008 ). Cell growth is also regulated by the membrane through endocytosis and exocytosis. In endocytosis, lipids and proteins are excreted form the cell membrane while substances are internalized ( Alberta et al., 2008 ). In exocytosis, lipids and proteins merge with the cell membrane thus increasing the cell size.
Overall, the cell is a complex structure that contains different organelles, which also perform varying important functions. Also, a eukaryotic cell is more structurally complex than prokaryotic given that it has a membrane bound nucleus and other enclosed membrane-bound organelles. The difference between membranous and non-membranous organelles is that the former ones have membranes that creates a boundary between the organelle`s content and the cytoplasm while in the latter, the organelle`s contents are continuous in the cytoplasm. The structure of the cell membrane is organized in a way that it supports cell growth, communication with the surrounding environment and maintains the veracity of the cell.
References
Alberta, B., Bray, D., Lewis, J., Watson, J. D., Raff, M., & Roberta, K. (2008). Molecular biology of the cell .
Michell, R. H., & Unknown, (2010). Membrane Structure: Membrane Structure . Amsterdam: Elsevier Science.
Orchard, G., & Nation, B. (2014). Cell structure and function . Oxford: Oxford University Press.
Tager, J. M., In Tager, J. M., In Azzi, A., In Papa, S., & In Guerrieri, F. (2009). Organelles in Eukaryotic Cells: Molecular Structure and Interactions .
