The Structural Compartmentaion of Mammalian Cells

The structural compartmentation of mammalian cells and the differing functions of these compartments. All mammals are eukaryotes and therefore have eukaryotic cells. These cells contain several organelles suited to a specific function they carry out within the cell. These eukaryotic cells contain a Nucleus, Mitochondria, Ribosomes, Rough and Smooth endoplasmic reticulum, Golgi apparatus and various other organelles. Most of the organelles are separated from each other by a membrane, these membranes are based on lipid bilayers that are similar to each other.

The organelles membrane is there to keep the contents of each organelle separate from the rest of this cell. The membrane consists of a lipid bilayer that may have channels in order to allow the transport of specific molecules which are needed somewhere else in the cell. An example of this is proteins produced by the ribosomes are then moved to the Golgi apparatus in which they are processed and then sent to the correct part of the cell. | Fig 1 – Diagram of a nucleusSource: http://cdn. nursingcrib. om| The nucleus is a large organelle surrounded by a double membrane nuclear envelope; the nuclear envelope contains many pores to allow substances such as tRNA and mRNA to move between the nucleus and the cytoplasm. The nucleus contains most of the cells genetic material in the form of DNA. The DNA and proteins that make up the contents of the nucleus is known as the chromatin. DNA stored in the nucleus codes for different amino acids and proteins to be produced, depending on which genes are being expressed decides what proteins are produced and ultimately the function of the cell.

At the centre of the nucleus is a nucleolus which is where ribosomes are manufactured. A diagram of a nucleus can be seen in figure 1. The double membrane keeps the nucleus separate from all the other organelles and serves as a barrier to prevent molecules diffusing freely into and out of the nucleus. The outer membrane has a structure similar to the rough endoplasmic reticulum with ribosomes scattered across it which are used to make proteins in a process known as translation. The mitochondria are the site in a cell that generates most of the cells energy in the form of ATP.

Oxygen is used in a process called aerobic respiration to produce lots of ATP. The mitochondrion consists of an outer and inner membrane composed of phospholipid bilayers. The inner membrane contains several folding’s forming a structure known as cristae. The cristae increase the surface area of the mitochondria allowing more ATP to be produced. The part enclosed by the inner membrane is the matrix. This matrix contains most of the mitochondria’s proteins. The matrix contains several enzymes needed to synthesise ATP. The ATP produced in the mitochondria is transported to other parts of the cell that require energy.

The ribosome is an important organelle for protein synthesis, it is the site at which the genetic code is converted into protein molecules. It is responsible for a process called translation which converts mRNA into an amino acid chain. The mRNA determine the order of the tRNA molecules that bind to the codons. The order of these tRNA molecule ultimately decide the amino acid chain that will be produced and hence the protein being produced. The proteins produced detatch themselves from the ribosome and move to other parts of the cell where they are needed.

The ribosome is very large composed of many molecules including RNA and proteins. The ribosome is composed of two sub-units, a larger one and a smaller one, each of which have distinct shapes. As protein synthesis is very important to cells there are usually large numbers of ribosomes found throughout a cell. Ribosomes are usually found floating freely around the cell however they are sometimes found bound to the endoplasmic reticulum. The endoplasmic reticulum is the transport network for molecules. It is made up of several tubes and sacs.

The space inside of the endoplasmic reticulum is the lumen. The function of the endoplasmic reticulum depends on the cell type. It is comprised of a rough endoplasmic reticulum and a smooth endoplasmic reticulum. The Rough endoplasmic reticulum has ribosomes attached to its surface which is what causes it to be rough. “The membrane of the rough endoplasmic reticulum forms large double membrane sheets that are located near, and continuous with the outer layer of the nuclear envelope”[1]. Proteins are synthesized in the rough endoplasmic reticulum.

The smooth endoplasmic reticulum is responsible for synthesizing lipids, metabolizing carbohydrates and regulating calcium levels. Lysosomes are also found in most eukaryotic cells. They contain several used to break down worn out cellular components and bacteria. Lysosomes are highly packed spherical vacuoles but have a large variation in size depending on the materials they have taken up for digestion. The lysosome removes any unwanted material inside the cell by secreting these digestive enzymes onto them. Lysosomes protect the cell from foreign bacteria which could be harmful.

They operate in a low PH which is maintained by a membrane around the lysosome, this reduces the risk of the enzymes digesting their own cell. The Golgi apparatus packages proteins inside the cell and are then sent to their destination. The Golgi apparatus is found within the cytoplasm of eukaryotic cells. It is composed of stacks known as cisternae. “The Golgi apparatus is integral in modifying, sorting and packaging these macromolecules for cell secretion”[2]. Proteins synthesized by the rough endoplasmic reticulum are modified in the Golgi apparatus.

The Golgi apparatus is also responsible for transporting lipids around the cells and also producing lysosomes. All of these organelles have different functions and structures but work together to determine the overall function of the cell. The amount of each organelle greatly depends on its function, for example muscle cells will contain lots of mitochondria to produce more ATP as muscles require large amounts of energy. Bibliography [1] Shibata, Yoko; Voeltz, Gia K. ; Rapoport, Tom A. (2006). “Rough Sheets and Smooth Tubules”. Cell 126(3): 435–439. [2] “Regulated Secretion (Golgi): The Movie”. North Dakota State University.