By: Prof. Dr. Seyed Saeid Zamanieh Shahri, MD and Prof. Dr. Sonia Sayyedalhosseini, MD
*Cell stores: As we said, organelles are living components inside the cytoplasm, but inside the cytoplasm there are non-living components called cell stores or cell inclusions. These inclusions are stored inside the cytosol. In fact, cell inclusions are the same substances stored in the cytosol, such as glycogen, which is stored in muscle and liver cells, and melanin, which is stored in skin and hair cells. The most important cell inclusions are nutrients and pigments. Stored nutrients include protein, carbohydrates, and fat. Pigments stored in the cell include exogenous pigments such as carotene and endogenous pigments such as hemoglobin, lipochrome, and melanin. Protein is usually not stored in the cell except in liver cells, filamentous cells, and Leydig cells. Carbohydrates are stored exclusively in the cell as glycogen, and are stored most of all in liver cells and striated muscle. This substance is broken down into glucose when necessary to produce energy.
So sugar is stored only in the form of glycogen in the liver and striated muscle cells. Glycogen is always stored in the cytoplasm, but in diabetes and storage diseases, it also accumulates and is stored inside the nucleus. Fat is stored more than any other substance in the form of droplets in the fat cell and provides a valuable source of energy.
*Pigments: Pigments are colored substances that are stored in special cells called chromatophores, such as the colored cells of the eye. Pigments are divided into two categories: external (exogenous) and internal (endogenous).
*External pigment: Rarely, pigments have an external origin, such as carotene found in carrots and tomatoes.
*Internal pigment: Most pigments have an internal origin and are made inside the body by special cells. The most important internal pigments are lipochrome (lipofuscin), hemoglobin, and melanin.
Before concluding the topic of the cell, I consider it necessary to mention this point that, given the advancement of technology and the application of biotechnology in medical science, a brief acquaintance with the basic concepts of the cell provides a better understanding and comprehension of the pathophysiological processes of diseases.
*Structure of the cell membrane: The cell membrane, sometimes called the plasma membrane, is a thin, flexible, elastic double-layer membrane 7 to 10 nanometers thick, which is composed almost entirely of protein and lipid. The approximate chemical composition of the cell membrane is: protein, phospholipid, cholesterol, other lipids.
The cell membrane is a very thin and flexible boundary that both protects the contents of the cell and controls the transfer of materials into or out of the cell. This membrane is made of two layers of lipid molecules with protein molecules between them. Transmembrane proteins act in the transfer of materials, and membrane surface proteins act as markers and receptors.
*Cell membrane proteins: The spherical masses that float in the lipid bilayer are membrane proteins, most of which are glycoproteins. So, there are two types of proteins in the cell membrane: global protein and peripheral protein.
*Cell membrane carbohydrates: Carbohydrates in the cell membrane or glycocalyx are almost always present in combination with glycoprotein protein and lipid (glycolipid). In fact, the majority of global cell membrane proteins are glycoproteins, but about one-tenth of the cell membrane lipid molecules are glycolipids. The
glyco or sugar part of these molecules almost always protrudes towards the outer surface and hangs outward from the cell surface. Carbohydrates attached to the outer surface of the cell membrane have a negative electrical charge and cause a negative charge on the outer surface of the cell. They cause adjacent cells to stick together. They act as carriers of hormones, including insulin, and enter into chemical reactions.
*Function of the cell membrane: The cell membrane has the following capabilities and functions: selective permeability, wave conduction, receptor properties, semipermeable properties, the ability to produce pseudopods, the ability to transport and transfer materials, enzymatic and control capabilities, antigenic properties, communication with the environment and other cells.
*Nucleic structure: The nucleus is one of the largest and most visible cell organelles that is present around the center of the eukaryotic cell as a distinct and large body. The shape of the nucleus is spherical or elliptical and its number is often the same. In some cells, such as liver cells and some bladder lining cells and stomach parietal cells, two nuclei are seen. Some body cells, such as striated muscle cells and osteoclasts, have multiple nuclei. The nucleus is the control center of the cell and has a nucleoprotein structure. The most important chemical compounds of the nucleus are nucleic acids and proteins. Nucleic acids include ribonucleic acid and deoxyribonucleic acid, which are concentrated in the nucleus. The percentage of nuclear proteins is often basic proteins. The basic proteins of the nucleus are histones. In fact, histones are the most abundant chromatin protein.
