Cell Membrane
Introduction
A biological membrane is a selectively permeable barrier that functions as a separating or enclosing membrane in living things. Biological membranes encompass a phospholipid layer with hydrophilic heads and hydrophobic tails (Voet 2012). The phospholipid layer is instrumental in cell-cell communication, in addition to facilitating transportation of ions and chemicals. The phospholipid layer also forms a fluid matrix that enables lateral diffusion and rotation of proteins, thereby aiding in physiological functioning (Dougherty et al. 1987). Membrane proteins contained within the phospholipid bilayers catalyse various chemical reactions, in addition opt forming strong links with the lipid bilayer (Lein et al. 2015). On the other hand, peripheral proteins which form a membrane asymmetry are easily dissociated from the membrane due to weak interactions (Voet, 2012). On the other hand, oligosaccharides are linked to phospholipids via covalent bonds. Oligosaccharides are involved in cell-cell adhesion and cell recognition functions (Alberts et al., 2002).
Body one
The cell surface membrane is a term used in reference to a biological membrane that acts as a barrier between the interior of the cells on the one hand, and the outside environment, on the other hand (Voet 2012). The cell surface membrane is described as being selectively permeable, meaning that it permits certain components such as organic molecules and ions while also controlling the movement of other substances out of and into the cells (Lein et al. 2015). The cell membrane consists of lipids, carbohydrates, and proteins. There are three classes of lipids contained in the cell membrane: phospholipids, sterols, and glycolipids. Each of these classes of lipids differ in terms of content, based on the type of cell. However, phospholipids tend to be the most abundant of the three. Non-covalent bonds hold the entire phospholipid layer in place. The most predominant carbohydrates in cell membranes are glycoproteins. Carbohydrates are essential in lymphocyte homing and cell adhesion, among other functions (Gray et al. 2002). Nearly 50% of the membrane volume is made up of proteins (Gray et al. 2002) which execute various biological functions, including surface recognition, cell-cell contact, signaling, transporting substances into and out of the cell across the cell membrane, enzymatic activity, and cytoskeleton contact.
Body two
All eukaryotic cells contain a nucleus as an organelle enclosed in the membrane. The inner membrane contains various proteins that aids in the attachment of chromatin to the nuclear envelope, in addition to aiding in nucleus structural organisation. It also surrounds the nucleoplasm. The nuclear lamina which covers the inner nuclear membrane plays a role in chromatin function, in addition to providing stability to the nuclear membrane (Hetzer 2010). Nuclear pores act as a link between the outer and inner membrane (Goergatos 2001).
The outer membrane contains a high concentration of proteins that are in turn involved on mechanosensory function and nuclear positioning (Burke & Roux 2009). Fitchman et al. (2010) opine that the outer nuclear membrane also plays a key role in protein binding since it combines with the inner membrane thus forming nuclear pores.
Body three
All eukaryotic organisms contain the mitochondrion, which is described by Henze, Martin and Martin (2003) as a “double membrane-bound organelle”. Nonetheless, red blood cells for example do not have mitochondrion. Several organisms have also been shown to transform or reduce their mitochondrion into other forms of structures (Henze et al. 2003). The outer membrane of the mitochondrion surrounds the whole organelle. It is made up of phospholipids and proteins in the same quantities to that contained in eukaryotic plasma membrane. The mitochondrial outer membrane also contains porins in large quantities. These are in the form of essential membrane proteins. Translocase, a large type of multi-subunit protein located within the outer membrane is actively involved in signaling sequence to permit the entry of larger proteins into the mitochondrion. Translocate then aids in the active movement of these proteins across the cell membrane. The enzymes contained in the outer membrane play a key role in facilitating such diverse activities as fatty acids elongation, tryptophan degradation, and oxidation of epinephrine (Burke & Roux 2009 ). Examples of enzymes involved in these activities include fatty acid Co-A ligase and monoamine oxidase. In case the outer membrane is disrupted, this could trigger the leaking of proteins held within the space in the inter-membrane into sytosol, thereby resulting in cell death (Henze et al. 2003).
In terms of function, the key role of mitochondrion is to generate energy in the form of ATP. The mitochondrion also play another role namely, that of regulating cellular metabolism (Voet et al., 2006). Mitochondria contribute towards cell survival through different means. For example, they are involved in the storage of calcium ions, thus enabling cells to maintain electrically charged particles in their right concentrations (Lein et al. 2015). These particles are in turn crucial in such activities as muscle contraction and blood clotting. Also mitochondria are involved in the synthesis of iron compound responsible for carrying oxygen in red blood cells to the various tissues of the body. Moreover, mitochondria function as the initial generation sites for such steroid hormones as estrogen, testosterone, cortisol, and estrogen.
Body four
Plasma membrane
This is an outer membrane or biological cell membrane consisting of phospholipids bi-layer with proteins embedded in it. The plasma membrane fulfils various functions. First, plasma membrane acts as a barrier between the cell outer environment and its contents. In this case, the plasma membrane helps to regulate what leave the ell and what enters the cell (Fichtman et al. 2008). Secondly, the plasma membrane only permits selected substances to enter the cell while preventing other substances from entering. This selective function is vital in crucial in protecting the integrity of the interior part of the cell (Voet 2012). Thirdly, plasma membrane acts as the foundation for attachment of cell wall or cytoskeleton in certain organisms. In this case, the cell membrane plays a supportive role to the cell and assists in maintaining the cell’s shape. According to Georgatos (2001), the plasma membrane is predominantly made up of lipids and proteins. Lipids afford flexibility to the membranes, while proteins check and uphold the chemical climate of the cell and aids in the movement of molecules across the membrane.
Golgi apparatus
Most eukaryotic cells contains the Golgi apparatus/body/complex is yet another organelle (Pavelk & Mironov, 2008). There is an intimate relationship between the structure of the Golgi apparatus and its structure. For example, individual stacks of the Golgi apparatus are characterized by various collections of enzymes, permitting for further processing of cargo proteins (Nakano & Luini 2010). Still on the Golgi stacks, enzymatic reactions take place completely near the membrane surfaces of the Golgi apparatus. The Golgi apparatus is also involved in protein modifications and in proteoglycans formation (Day, Staehelin & Glick 2013).
Conclusion
Both animal and plant cell membranes share certain common features. From a structural context, animal and plant cells are similar seeing as they are both eukaryotic cells. Accordingly, they contain common organelles bound to the membrane, including mitochondrion, nucleus, and Golgi apparatus. Their structure and functions are also inter-related.
References
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