Cell: The Importance Of Biological Membranes

The cell membrane is known to be the cell gate and door. It is an important biological structure that plays an important role in different biological processes such as protection, filtration, transport.

Biological membranes are said to be a lipid bilayer(due t the presence of two layers of lipids with hydrophobic and hydrophilic tails ), they are composed of different classes of lipids, different classes of proteins, and cholesterol that interacts together. This combination of molecules is referred to as the fluid mosaic model: It was established in the 70th by two American biochemists, It describes the lipid bilayer as a dynamic, fluid, and flexible membrane due to its physiochemical properties and compositions.

In addition to the role of the biological membranes in transport and protection, it is also involved in the cell signaling process. Biological membranes are responsible for receiving and transmitting the messenger in a signaling cascade due to its receptors

In this essay, we will first focus on the physicochemical that participate in the membrane fluidity and flexibility then we will talk about the role of the biological membrane in the cell signaling process.

The membrane fluidity flexibility is described as the ability to change states and shapes. It could exist in a rigid structure or a gel-like structure this is determined by the transient temperature which is the temperature at which the membrane change is fluidity from to dorm a more crystalline gel stature. In fact, The membrane can be a packed state or more loose states and this depends on the type of lipid it is composed of. The unsaturated fatty acids ( ex linolenic acid, fatty acids chain with one more double-bound) help the membrane to assemble less tightly, therefore, decreasing the transition temperature at 60 degrees (1), this due to the capacity of unsaturated fatty acids to bend at 30° which help to create some spaces know as elbow room which helps with membrane fluidity which makes it easier to reach the fluid state.

Another factor that helps the membrane fluidity is how long are the fatty acids chains. Short chains tend to lower also the transition temperature because it is easier to change shape when the fatty acids chains are less longer and fewer.

In addition, the presence of cholesterol also plays a role in establishing membrane fluidity. It is considered a two-direction role; it is able to maintain and sustain the membrane at high temperature and on the other side at low temperature, it prevents the membrane to pack tightly. The cholesterol molecule is able to decrease membrane close-packed structure and create a certain level of fluidity.

Another characteristic of the lipid bilayer is its two-dimensional states in which lipids molecules but also protein can move, rotate and change state.

Interaction of different molecules of the biological membrane is able to form microdomains named lipid rafts.

Lipid rafts are a small plate full of cholesterol and sphingolipids and a GPI attached protein attached covertly. These rafts are believed to be energetic and mobile structures that contribute also to the membrane fluidity and flexibility

The last factor is the availability of pholipids bilayer. Indeed at low-temperature kinetic energy available decreases causing the pholipids to get close to each other at constant higher temperatures, the phsospilipis are able to disturb membrane force to stay fixed and therefore increase membrane fluidity.

The properties cited above not only participate in membrane fluidity but also play an important role in the cell signaling cascade.

The first property is the presence of cholesterol which tends to have a role in reports.

In fact, recent students showed that Cholesterol is able to regulate G protein couples cascade as it is important for the Hedgog transduction in the synthesis of the ligand and also in transmitting the message to the other cell. Furthermore, another derived product of cholesterol: oxysterol is believed to induce ATP binding to eh liver receptor.

The signaling cascade can also be affected by the type of fatty acids present on the plasma membrane.

Indeed Polyunsaturated fatty acids are thought to be involved in promoting the activation a nuclear factor kappa B (NFkB) by damaging the lipopolysaccharide (LPS)-mediated activation of TLR4

Lipid rafts are known to play a role in cell signing as they provide a platform for the cascade receptor. In the tyrosine kinase cascade, the lipid rafts help to keep the receptor and protect it from nonraft enzymes. In addition to that lipid rafts also participate in the cytokinesis signaling cascade. Cytokines caused is controlled by comprtamentailyion of receptors located on the lipid rafts to establish the specificity of the signaling nonetheless microdomain distribution is also important in cytokines caused and can alter its responses

Phospholipids are believed to be a key player in cell signaling. In fact, they are transferred to a second messenger by enzymes such as phloplipases. Phosphalipze when activated by an extracellular ligand is able to break down hydrolyzes phosphatidylinositol 4,5-biphosphate (PIP2) into inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG) [10]. Where DAG is able to stimulate protein kinase c to generate a calcuicom level increase

The last participation of membrane in cell sibling is the infection between protein and lipids which prompt cell trafficking. Glycerolphospholipids are able to promote membrane fusion by changing SNAREs

Biological membranes are believed to be flexible and fluid to their composition, molecule interaction, and chemical properties. Its fluidity is believed to play an important role in many sibling cascades. In addition to lipid bilayer contribution on cell sibling it is nowadays believed to play an important role in regulators that can be used to treat several human autoimmune diseases