Plasma Membrane for Peptides and Proteins- myassignmenthelp.com

Question: Discuss about thePlasma Membrane for Peptides and Proteins. Answer: Plasma membrane is a biological and outer membrane of cell found in both prokaryotes and eukaryotes. It is semi permeable in nature and acts as a barrier between inner cell and outer cell surface. This membrane is composed of tightly packed phospholipid bilayer which permits movement of only selected molecules through it. A single molecule of phospholipid consists of a group of phosphate known as head on one end and on another end is the lipid tail which is made by 2 side by side chains of fatty acids. Head of phosphate group is negatively charged, that makes it hydrophilic and polar in nature so it is attracted to water of both intracellular and extracellular environment(Yeagle, 2009). Similarly, tails are nonpolar in nature i.e. it is hydrophobic in nature which repels water. So, the membrane has hydrophobic interior and hydrophilic exterior. As it is made up of 2 layers of phospholipids, tails of one-layer face towards the tail of other layer and these assembles at the boundary of two layers. Phospholipids are amphipathic molecules as it contains hydrophobic as well as hydrophilic regions. Some of lipid tails contains saturated fatty acids and other contains unsaturated fatty acids and because of which tails are continuously moving(Soult, 2016). The lipid bilayer forms the basic structure of the plasma membrane and consist of several proteins which are of two types: integral protein and other is called peripheral protein. Integral proteins like channel protein, cell recognition proteins, glycoproteins etc are present in the cell. Glycoproteins act as a receptor and are used for cell recognition. Many lipids with short carbohydrate chains are also attached on the membrane on extracellular side. Peripheral protein is present on the outer or inner surface of the phospholipid bilayer and can also be found on the surface of integral protein which serves specific purpose for the cell. It also consists of lipids like cholesterol which helps to maintain the fluidity of the membrane. One of the most important function of the plasma membrane is that it helps in the regulation of the concentration of substances like fatty acids, amino acids, wastes like carbon dioxide and ions like sodium, potassium etc inside the cell. Plasma membrane allows only few non-polar substances like oxygen, alcohol, carbon dioxide to pass through the lipid bilayer as the tails are non-polar in nature. But other water-soluble substances like amino acids, glucose and electrolytes need some support to pass through it as they are resisted by the hydrophobic tails of membrane. Each substance needs either passive transport or active transport systems to move across the membrane. Passive transport is a process of movement of any molecules across the plasma membrane without use of any cellular energy via concentration gradient or electrical gradient(Cooper, 2000). In contrast to this, active transport is a process in which energy in the form of ATP (adenosine triphosphate) is required for movement of substance through the membrane against concentration gradient(NJ MJ, 2015). It also often needs carrier proteins for the transport process. Oxygen easily diffuses across the plasma membrane from outer cellular surface to inner cellular surface using its own intrinsic kinetic energy as it is more concentrated outside the membrane. As we know that cells use oxygen very rapidly during metabolism, the oxygen concentration inside the cell is very low in comparison to outside the cell. So, oxygen from the interstitial fluid diffuses by the process of simple diffusion through the cell membrane inside the cell. Oxygen can directly pass through the membrane by passive diffusion as it simply dissolves in the lipid bilayer and diffuses across the layer(Albert, Johnson, Raff, Roberts, 2002). Then it dissolves in the aqueous solution inside the cell on the other side of membrane. It does not require any membrane protein for transportation. The direction of transport is simply determined by the concentration gradient. In this process, external source of energy or carrier protein is not required. Sodium being the charged molecule cannot pass through the plasma membrane. For the movement of such molecules across the membrane requires specific transport system is used which helps to control the entry and exit of most molecules in the cell. It also needs specific protein called channel protein to transport molecules like potassium, sodium, calcium etc, through the membrane. These proteins form small open pores in the lipid membrane and allows these molecules of appropriate charge and size to pass through the membrane. One of the most common active transport is called sodium potassium pump. In this process ATP is used to force to pass potassium ions inside the cell and sodium out from the cell. This pump helps to maintain high amount of sodium outside the cell. Whenever cell needs sodium ion, pump opens a passive sodium channel and due to concentration gradient sodium enters inside the cell. There are membrane proteins called symporters that helps in secondary active transports. References Albert, B., Johnson, A. J., Raff, M., Roberts, K. (2002). Molecular Biology of the Cell. NCBI. Cooper, G. M. (2000). The Cell, 2nd edition: A Molecular Approach. NCBI. NJ, Y., MJ, H. (2015). Getting Across the Cell Membrane: An Overview for Small Molecules, Peptides, and Proteins. NCBI, 29-53. Soult, A. (2016, December 7). Phospholipids in Cell Membranes. Retrieved from ChemistryLibreTexts: https://chem.libretexts.org/LibreTexts/University_of_Kentucky/UK:_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_14:_Biological_Molecules/14.3:_Phospholipids_in_Cell_Membranes The Plasma Membrane: Structure. (2104, July 8). Retrieved from Anatomy Physiology: https://anatomyandphysiologyi.com/the-plasma-membrane-structure/ Yeagle. (2009, December 10). Cell Membrane Features. Retrieved from Research article: https://www.researchgate.net/publication/227992332_Cell_Membrane_Features