By: Prof. Dr. Seyed Saeid Zamanieh Shahri, MD  and  Prof. Dr. Sonia Sayyedalhosseini, MD

Structural proteins in cells are mainly present in the form of long and thin filaments, the most obvious use of which is to provide a contractile mechanism in muscles. Globular proteins mainly play the role of cellular enzymes. The most important lipids (fats) in most cells are phospholipids and cholesterol, which make up about 2 percent of the cell mass. The special importance of these two types of fat is that they participate in cell membranes due to their insolubility. In addition, some cells have large amounts of triglycerides (neutral fats). In cells, triglyceride makes up to 95 percent of the cell mass. This fat is the main storehouse of energy-giving nutrients for the body, which is stored in fat cells and broken down when needed and used to produce energy for the body.

The most important ions in the cell are potassium, magnesium, phosphate, sulfate, bicarbonate, and small amounts of sodium, chlorine, and calcium. The ions provide minerals for cellular chemical reactions and are required for the transmission of electrochemical impulses in nerve and muscle fibers. Carbohydrates, except for glycoproteins, which have a structural function, play a role mainly in the nutrition of the cell. The carbohydrate content of most cells is about 1% of the cell mass, but in muscle cells it increases to 3% and in liver cells to 6%.

Physical structure of the cell:

The physical structure of the cell is made up of three main parts: the cell membrane, the cytoplasm, and the nucleus. Each cell has a separating boundary with the environment called the cell membrane.

Inside the cell, there are small structures called organelles, these organelles are located in a special gelatinous environment called the cytoplasm. The nucleus with the nuclear membrane is located inside the cell and the nucleolus is located inside the nucleus.

Cytoplasm is called the basic substance of life, which is a colorless, semi-fluid, viscous, and flexible substance, which chemically contains the most important elements in its composition, carbon, oxygen, hydrogen, and nitrogen. From the combination of these elements, water, salts, and biomolecules are formed. The cytoplasm has a state between a sol and a gel, and the conversion of these two into one is one of the important factors in cytoplasmic stimulation. A sol is a liquid colloidal solution, while a gel is called a gelatinous colloid.

The cytoplasm is surrounded by a cell membrane. Inside the cytoplasm are living membrane-bound components called organelles and non-living membrane-bound components called cell inclusions. Apart from the soluble organelles and inclusions, what remains as a uniform liquid in the cytoplasm is called cytosol or hyaloplasm. This liquid contains enzymes and mineral salts and has a large amount of actin and intermediate filaments that form the scaffolding or skeleton of the cell or cytoskeleton. Cytoplasmic enzymes catalyze numerous biochemical reactions that form part of metabolism, so the components of the cytoplasm are: organelles, inclusions and cytosol of the cell skeleton. The metabolic processes of the cell are carried out by the cell organelles and each organelle has a specific and vital function. The most important cell organelles are: ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes and centrosomes. Now let’s examine the components of the cytoplasm. Inside the cytoplasm are turbinate’s of branched tubular structures and flat vesicles called the endoplasmic reticulum, whose tubules and vesicles are all connected and whose walls are made of a double-layered membrane similar to the cell membrane. This membrane is connected to the nuclear and cytoplasmic membranes. Substances formed in some parts of the cell enter its spaces and are then directed to other parts of the cell. The vast surface area of the endoplasmic reticulum and the enzyme systems attached to its membrane enable this organelle to carry out a major part of the cell’s metabolic functions.

Cytoplasm is called the basic substance of life and it is a colorless, semi-fluid, viscous and flexible substance whose most important elements in its composition are carbon, oxygen, hydrogen and nitrogen. From the combination of these elements, water, salts and biomolecules are formed. Cytoplasm has a state between sol and gel and the conversion of these two into one is one of the important factors of cytoplasmic stimulation. Sol is a liquid colloidal solution, while gel is called gelatinous colloid.

Cytoplasm is an intracellular substance that has a jelly-like consistency like egg white and is mainly composed of water, protein, fat, sugar and mineral salts in solution.

The cytoplasm is surrounded by a cell membrane. Inside the cytoplasm are living membrane-bound components called organelles and non-living membrane-bound components called cell inclusions. Apart from the soluble organelles and inclusions, what remains as a uniform liquid in the cytoplasm is called cytosol or hyaloplasm. This liquid contains enzymes and mineral salts and has a large amount of actin and intermediate filaments that form the scaffolding or skeleton of the cell or cytoskeleton. Cytoplasmic enzymes catalyze numerous biochemical reactions that form part of metabolism. Therefore, the components of the cytoplasm are organelles and cell inclusions.

The metabolic processes of the cell are carried out by the cell organelles, and each organelle has a specific and vital function. The most important cell organelles are: Ribosomes, the Endoplasmic Reticulum (E.R.), the Golgi Apparatus, Mitochondria, Lysosomes, and Centrosomes.

* Endoplasmic Reticulum (E.R.): Inside the cytoplasm, there are turbinated of branched tubular structures and flat vesicles called the endoplasmic reticulum, whose tubules and vesicles are all connected to each other and whose walls are made of a double-layered membrane similar to the cell membrane. This membrane is connected to the nuclear membrane and the cytoplasm.

Materials formed in some parts of the cell enter the spaces of the endoplasmic reticulum and are then directed to other parts of the cell. The vast surface area of the endoplasmic reticulum and the enzyme systems attached to its membrane enable this organelle to carry out a major part of the cell’s metabolic functions. There are two types of endoplasmic reticulum in the cell, rough endoplasmic reticulum (granular) and smooth endoplasmic reticulum (without granules).

To be continued