In this article I will discuss the composition of cells on the molecular level as far as molecules are concerned. The collection of molecules that are present in the cells is called protoplasm. The protoplasm of cells includes water and electrolytes and lipids in addition to carbohydrates. The first of which that is discussed here is water.
Water is the major constituent of the body mass in general and cells in particular. In the blood it makes part of the serum. Water has a high dielectric constant that enables it to dissolve many compounds including vitamins and proteins. The amount of water in the cells is tightly regulated by the osmolality of the extracellular fluid.
Osmosis is the the process in which water dffuses across the cellular membrane due to a gradient in the concentration of electrolytes between the interior of the cell and its exterior side of the cell. The amount of water in the cell can change by diffusion of water from the cell into the exterior space or vice versa.
The osmolality of blood is the main determinant of the amount of water that will diffuse across the cellular membrane. This is important when doing an infusion of saline solution into the body of dehydrated patients. It is usually important to infuse an isotonic solution so that the amount od water does not change due to a change in the osmolality of the blood as result of the infusion.
In the cellular water are electrolytes and proteins dissolved. The electrolytes have an immense importance in the regulation of various functions in the cell such as buffering role of the cell that is caused by the phosphate and bicarbonate ions. In addition metals have important role as cofactors for enzymes in the cells which catalyze biochemical reactions inside the body.
These cofactors are very important for the proper function of these enzymes. An example of such an electrolyte is magnesium ion. Other electrolytes are important due to their function in exciting nerve and muscle cells. The intracellular ion which is of extraordinary significance is potassium ion.
Other electrolytes which are also important are sodium ions which are predominantly found outside the cell. They are usually kept outside the cell using molecular pumps which pump sodium ions outside the cell using ATPase enzymes which catalyze this transport that requires energy to proceed.
Phosphate and bicarbonate ions function as buffers in the blood and the cells. Phosphate being less efficient as a buffer that the bicarbnate ions due to the range of pH that it functions at. Bicarbonate is the major buffer in the extracellular space.
Proteins are abundant in eukaryptic cells and are synthesized inside the cell according ro a translational process which uses bases of DNA molecules and converts it into amino acids code. This process of proteins synthesis is lacking in prokaryotes due to the lack of nuclei in these cells.
Amino acids are the building blocks of proteins. There are proteins in the cell which have structural roles and others that have functional roles. Proteins that have structural roles include the protein collagen of the connective tissue of the body. Enzymes are a group of proteins which have an extremely important role in the body.
They function usually by catalyzing biochemical reactions in the body. They usually have a cofactor which is usually a metal but can also be an organic molecule such as the cofactor thiamine. Enzymes have an active site which is the place where the catalysis takes place. They usually function by lowering the value of the free energy of Gibbs of these reactions.
Lipids are also an important group of compounds especially the molecule cholesterol which is part of the cellular membrane. In addition it is a precursor to steroidal hormones such as testosterone and aldosterone. Adipose cells are a type of cells in the body which constitute a large amount of lipids within them.
Metabolism of lipids and in particular fatty acids is important especially in the medical condition diabetes mellitus. In this condition fatty acids are metabolized to ketonic acids which have distinct clinical symptoms such as urine that smells like acetone in addition to developing metabolic acidosis.