Describe the structural compartmentation of mammalian cells and the differing functions of these compartments

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Describe the structural compartmentation of mammalian cells and the differing functions of these compartments

All mammalian cells are eukaryotic cells. They have a true nucleus and they are normally enclosed by a plasma membrane. In a typical eukaryotic cell, one would expect to have, along with a plasma membrane and nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, cytoskeleton etc.[3] These organelles are all membrane-bound structures, each have a unique role to play in the functioning of the cell. All these organelles are specific proteins and they all interact with each other to support the cell. However cells are different from each other. Cells differ from species to species and they also differ from different organs.[5] Every cell type has its own function and its function determines the quantity of each organelle. For example, we expect to find more mitochondria in a muscle tissue cell than in a skin cell. A muscle tissue cell needs to have extra production of ATP to allow for contraction whereas the skin cell does not need to do so. This assignment will give a brief overview of the structural compartmentation and their function of a typical mammalian cell with special focus on the plasma membrane and mitochondria.

Figure 1, a cartoon picture of a typical eukaryotic cell depicting all the compartments[2]

Plasma membrane contains the content of the cell. It holds the structural integrity of the cell but at the same time it is also very flexible to allow for movement. The membrane has three other important functions: it has ability to identity molecules and other cells on the surface; it has a selective barrier which allows the membrane to control the exchange of molecules in and out of the cell and it can communicate between cells with its receptor on the surface.[5] The plasma membrane is composed of a bilayer of phospholipids. A phospholipid molecule has a hydrophilic end and a hydrophobic end. When submersed in a watery environment, like the cytoplasm and the external environment, the phospholipid molecules coalesce and organise themselves into neat bilayer in which the hydrophilic end of the molecule is closest to the water and the hydrophobic end is facing 90° away from the water. The hydrophobic ends of the phospholipid stick together due to the hydrophobic interaction in which the non-polar molecules cannot form hydrogen bonds with water. Furthermore, the hydrophobic end also repels water and along with the hydrophobic interaction, the phospholipid line up in a bilayer fashion. Due to the fact that the hydrophobic interactions are very weak forces, the phospholipid bilayer is very flexible. On the other hand, due to the number of the hydrophobic interactions, it is relatively strong and is a barrier to other solvents making it suitable to maintain the structural integrity.[4,6] The plasma membrane’s recognition ability is due to the glycoproteins present on the surface. Glycoproteins are a sequence of glucose and other complex sugars on the protein peptide chain.[5] The sequence of glucose on the protein can be matched by a complementary sequence on another glycoprotein on the surface of cell plasma. If the sequences are complementary, the cells stick together and make contact allowing the formation of tissues and them organs. If the sequences are not complementary, the cells do not attach. This is important for growing organisms as there is a rapid production of new cells.

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Figure 2, a picture of a phospholipid bilayer with all the proteins[1]

One of the main functions of a plasma membrane is to allow molecule to be exchanged. There are several ways it can happen and it is helped by the structure of the membrane. The first type of diffusion is passive diffusion. The plasma membrane is fluid and gaps form in the phospholipid bilayer (due to the weak hydrophobic bonds), these gaps allows for small and/or non-polar molecules to pass through. This type of diffusion requires no ATP; it depends on the concentration gradient where molecules will move ...

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