3 Functions Of Proteins In The Cell Membrane – Each of us has thousands of proteins that perform many functions, and each protein has a unique three-dimensional structure that defines its function.For example, hemoglobin
A protein found in red blood cells that plays an important role in oxygen transport. It has four subunits of two different types (two alpha subunits and two beta subunits).
3 Functions Of Proteins In The Cell Membrane
The important relationship between protein structure and function is strikingly demonstrated by sickle cell anemia, an inherited disorder found in people with ancestry from Africa, the Middle East, the Mediterranean, or India. About 4 in 1,000 Americans of American descent (about 80,000) have sickle cell disease, and about 10% have sickle cell disease.
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People with sickle cell disease have an abnormal type of hemoglobin called hemoglobin S (instead of normal hemoglobin A). Hemoglobin S differs from hemoglobin A in that the amino acid valine is in the sixth position of the beta chain instead of the amino acid glutamate. Unlike glutamic acid, the side chains of valine are less polar and form sticky patches on the outside of each beta chain. However, when a large number of hemoglobin cells are deoxygenated, sticky spots formed by exogenous valine begin to attach to corresponding sticky spots on other hemoglobin molecules. increase. This creates long clusters of hemoglobin that deform red blood cells, giving them their characteristic sickle shape. This impairs the ability of red blood cells to clump together and circulate through small blood vessels (arterioles and capillaries). It also makes red blood cells more fragile, shortening their lifespan and leading to bleeding.
Acute exacerbations, called ‘cell crisis’, can be caused by deoxygenation of hemoglobin after strenuous exercise or infection. The disease can be widespread and can result in insufficient blood flow to the body, causing severe pain and complications such as stroke, kidney damage, and breathing problems.
Some proteins act as enzymes, proteins that activate specific biochemical reactions. Enzymes accelerate biochemical reactions, speeding them up significantly, making them about a million times faster. There are thousands of enzymes, each type performing a specific biochemical reaction. In other words, certain enzymes act only on certain reactants (substrates) to produce end products. The figure below shows the enzymatic degradation of the disaccharide lactose (substrate) to the monosaccharides galactose and glucose.
The three-dimensional structure of an enzyme contains specific binding sites to which substrates fit precisely, just as keys fit in specific locks.
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Upon substrate binding, the enzyme cleaves the substrate and releases the product. Although this cartoon depicts the breakdown of substrates, many enzymes synthesize new biochemicals by combining two substrates to create new products. A given mouth may contain thousands of different enzymes that trigger different reactions.
Biochemical reactions may require a whole series of steps, each step catalyzed by a separate enzyme. A good example is the series of reactions in which glucose is synthesized and produces cellular energy in the form of ATP (adenosine triphosphate).
(red, white, blue, and gray amino acids) are important protective enzymes found in tears, saliva, and mucus. Lysozyme’s job is to break down polysaccharides (polymers of sugars) that are the building blocks of bacterial cell walls. Initially, lysozyme is synthesized as a long polypeptide chain that folds in a characteristic way to form a globular protein with characteristic pockets. A bacterial polysaccharide (shown in green) binds to lysozyme. This is because the key fits perfectly in your pocket like it fits in your lock. Upon specific binding, lysozyme breaks apart bacterial polysaccharides.
Antibodies are protective proteins that recognize and bind to specific foreign substances by their three-dimensional structure. By binding to foreign proteins, they neutralize and mark them, facilitating their destruction and removal by immune cells. has a quaternary structure with The chains are connected to each other by disulfide bridges shown as ‘-S-S-‘ bonds on the right. After birth, each B lymphocyte can make antibodies against specific foreign samples. The portion of an antigen that is specifically recognized by an antibody is called an “epitope.” Essentially, an epitope is a specific portion of an antigen that has a specific molecular shape that corresponds to the protein binding site on an antibody.
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Watch the short video below for an explanation of antibody action. At the beginning of the video, red blood cells and white blood cells are shown flowing through a blood vessel. The next potato-shaped object you see represents a protein that begins to bind to a cell’s receptor. Green Y represents antibody binding to virus. Finally, the Medusa-like structures represent white blood cells that engulf and destroy tagged viruses in the body.
There are also structural proteins that are often long and fibrous, such as silk, keratin in hair, and collagen in muscles and tendons.
There are contractile proteins such as actin and myosin that provide muscle movement and movement between cells.
There are signaling proteins such as the hormone insulin, which consists of two polypeptide chains linked by disulfide (two sulfur) bridges.
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Insulin receptors (recognition proteins) are embedded in muscle cell membranes, fat cells, and other types of cells. Its function is to facilitate the absorption of glucose from the bloodstream by special glucose transport proteins that are normally present in cells in an inactive form. is called When an insulin molecule binds to the α subunit of the receptor, a chain reaction occurs within the cytosol (inside the cell) that activates GLUT4, translocates it, and inserts it into the cell membrane.
Apart from simple diffusion, proteins are also important for transporting polarized or charged molecules and large molecules across cell membranes.
Small molecules such as oxygen and carbon dioxide can diffuse across the lipid bilayer of cell membranes. The direction of movement depends on the direction of concentration. Substances with high intracellular concentration (e.g. CO
) diffuses out of the cell to the less concentrated side. Extracellular high-concentration substances (e.g., O
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However, many other substances cannot cross cell membranes by simple diffusion and require specialized mechanisms for transmembrane transport. Various transport proteins, often composed of protein subunits, provide a means of transporting charged and large substances by one of two mechanisms.
Polar molecules and charged ions cannot pass through lipid bilayers. Their passage depends on special transport channels created by proteins embedded in the cell membrane. Simple transport is passive in that it does not require the expenditure of cellular energy, and similar to simple diffusion, movement of molecules follows a concentration gradient from high to low concentrations. There is a specific protein for each substance transported by this mechanism, and transport is controlled by the cell. Substances such as glucose and amino acids are transported in this way. They bind to a carrier/carrier protein, and upon activation the carrier changes shape, translocating the molecule across the membrane. When the molecule is released, the carrier returns to its original shape (conformation).
Active transport is also based on transmembrane transport proteins, but this process can transport substances against recycling. This means that potassium can be placed inside the cell even though the concentration of such ions as potassium is higher inside the cell than outside. This is because cellular energy (ATP) is depleted.
Therefore, proteins play an important role in cell function. Many are embedded in cell membranes or spread across lipid bilayers and play important roles in recognition, signaling, and trafficking. Every effort has been made to follow index style conventions, but there may be some inconsistencies. If in doubt, refer to the appropriate body guide or other resource.
Intracellular Aspects Of The Process Of Protein Synthesis
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Membrane, in biology, a thin layer that forms the outer boundary of living cells or internal cellular compartments. The outer boundary is the plasma membrane, and the inner membrane portion is called the organelle. Biological membranes mainly have three functions. (2) they have receptors and channels that receive specific substances such as ions, nutrients, waste products, and metabolites that mediate cellular and extracellular activity through them;