Outline the properties displayed by membranes and how these
relate to their functions and locations in eukaryotic cells
Membranes are phospholipid polymers made up of fatty acids, glycerol and phosphate as well as an amine or alcohol group. They are arranged with hydrophilic heads on the outside layer and the hydrophobic tails on the inside. Eukaryotic cells are found in both animals and plants, and are defined by the presence of organelles within them. Organelles are structures within the cell dedicated to performing certain processes, such as cellular respiration, protein folding or locomotion. Membranes play a vital role in carrying out these processes, their specific architecture and inherent attributes factor crucially into their contribution to organelles.
Mitochondria, found in almost all eukaryotic cells, are a good example of form fitting function for membranes in eukaryotic cells. Mitochondria are the site of cellular respiration in the cell, and their number is determined by the cells metabolic activity. They are enclosed by two membranes, both with a phospholipid bilayer and each with a distinct set of embedded proteins. The first membrane is the smooth outer membrane, and the second is the inner membrane which is highly convoluted and has numerous infoldings known as cristae. Within the inner membrane there is also the mitochondrial matrix, which holds many respiratory enzymes and free ribosomes. The convoluted nature of the inner membrane and it’s cristae allow it to hold these proteins, while also providing its large surface area; both attributes are ideal for cellular respiration.
Another such favourable pairing of structure and function exists within the Golgi apparatus, which is responsible for collecting products produced by the endoplasmic reticulum (ER), storing or modifying these products as necessary and then sending them back to the ER. The Golgi apparatus is composed of many flattened membrane stacks, collectively known as cisternae and individually as cisterna. In each cisterna, the membrane serves to separate the cisternas internal space from the cytosol.
However, membranes factor into the overall operation of the Golgi apparatus more specifically. Each side of a stack of cisternae has its own structural polarity, the poles making up the cis and trans faces of the Golgi apparatus. This unique polarity distribution allows the cis face to receive vesicles from the ER, then move these products to the trans face to be extricated from the apparatus and sent back to the ER by newly formed vesicles. Once again, the properties of these membranes directly influence their ability to perform critical functions within the eukaryotic cell.
In summary, membranes play a vital role in the function of organelles in eukaryotic cells, their inherent properties tailoring specific membranes to carry out a diverse range of tasks in various organelles. A convoluted structure aids cellular respiration in the mitochondria, polarity allows for transportation in the Golgi apparatus, and selective permeability allows membranes across these organelles to separate inside from out, protecting their contents and the important reactions therein.