The plasma membrane is composed of both lipids and proteins. Its fundamental structure is the phospholipid bilayer that serves as a constant barrier between two aqueous sections. These sections are present inside and outside the plasma membrane. Lipids, as well as proteins, have specific functions to be performed within the plasma membrane. Proteins are responsible for the selective transport of molecules within the structure of the plasma membrane. This paper will discuss the anatomy of the plasma membrane and will also describe the movement of the oxygen and sodium ions across the plasma membrane.
High-magnification electron micrographs reveal the structure of plasma membrane. The plasma membranes of animal cells have four main phospholipids that are named as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, as well as sphingomyelin(Ross, Pawlina, & Histology, 2006). These serve as barriers in the plasma membrane. Along with phospholipids, glycolipids and cholesterol are also present in the structure of plasma membrane. But glycolipids are minor membrane components that consist of about 2% of most plasma membranes. Cholesterol is present in more concentration in the cell. In addition to this, proteins are accountable for functioning explicit membrane roles. They also have a larger size as compared to lipids, thus, there are fewer protein molecules as compared to lipid molecules. The fluid mosaic model allows the comprehensive analysis of the plasma membrane. There is no back and forth movement of proteins and phospholipids as these are implanted into a fluid lipid bilayer.
The plasma membrane is responsible for the separation of the external and internal environment of the cell. It is semi-permeable in nature and it ensures the specific molecules and ions to enter into the cell freely along with the free removal of the waste products. This movement of materials is due to the presence of the specific transport proteins in the plasma membrane(Alberts et al., 2013). These proteins are required for the movements of ions also as for oxygen ions and sodium ions (Pittman, 2013). Oxygen moves across plasma membranes through a process of diffusion along with water and carbon dioxide. It is the passive transport of oxygen and this is due to the differences in concentration of oxygen on both sides of the cell membrane. When there is oxygen-rich blood and it is passing through a cell then oxygen gets diffuse through the cell membrane and reach the area, where there is less oxygen. In this way, oxygen moves into the cell. If there is no centration gradient present at the point of transfer of oxygen, then it can be transported also using the energy in the form of ATP.
Moreover, sodium also moves in and out of the cell membrane. Due to the difference in a concentration gradient, sodium ions move from the cell and enter into the environment. For this purpose, there is a special mechanism responsible for the regulation of ions concentration. This is known as a sodium-potassium pump(Alberts et al., 2013). It is responsible for the transport of two potassium ions into the cell along with the expelling of three sodium ions. Sodium concentration should be high outside the cell as this concentration serves as cotransporter. With the help of sodium concentration, glucose is moved into the cell. Here, there is a use of active transport process that uses energy by the hydrolysis of ATP. There are some channels that are responsible only for the transport of sodium and thus they keep the quantity of sodium to the extent as needed by the body.
Alberts, B., Bray, D., Hopkin, K., Johnson, A., Lewis, J., Raff, M., … & Walter, P. (2013). Essential cell biology. Garland Science.
Pittman, R. N. (2013). Oxygen transport in the microcirculation and its regulation. Microcirculation, 20(2), 117-137.
Ross, M. H., Pawlina, W., & Histology, A. (2006). A text and atlas with correlated cell and molecular biology.