In this article I will discuss the biology of the cellular membrane and the biology of the organelle inside the cell, which is called the mitochondria. In addition, I will discuss the important process of protein trnaslation which occurs on the cellular ribosomes. The cell is composed of a protoplasm and a cellular membrane. Inside the cell there are several organelles which are suspended within the cellular cytoplasm.
The cellular membrane that encircles the contents of the cells is a physical barrier which is a very selective for the passage of chemical compounds. Not every compond can penetrate this membranous barrier. The membrane is composed of phospholipids bilayer. Therefore it is only permeable to lipid soluble compounds such as steroids.
Polar compounds do not readily penetrate this membranous barrier due to the repulsion between the polar compounds and the hydrophobic part in the cellular membrane. Exception to this is the molecule water which can readily penetrate the phospholipid bilayer in the cellular membrane.
Passage of water as well as some other compounds that penetrate the cell by a diffusional process is controlled by the concentration gradient of these componds across the cellular membrane. The fact that the cellular membrane is not freely permeable to every compound can offer protection for the cell against noxious compounds.
Benzene molecule is a lipid soluble compound that can readily penetrate the cellular membrane due to itas hydrophobic character. Benzene is a special noxious compound for humans and animals as it can cause mutation of the DNA molecule by the process of penetrating between two adjacent DNA bases due to its flat structure.
Benzene is used as a solvent in the organic chemistry lab and is used also as a fuel due to its hydrocabon structure. Other compounds such as acridine and other polycyclic aromatic hydrocarbons which have similar structure to benzene can also penetrate the cellular membrane easily and can cause mutation in the DNA molcule or cancer due to its penetrating ability between the DNA bases.
There is also besides diffusion across the cellular membrane another form of transport across the cellular membrane. This type of transport is called active transport. This active transport requires energy to proceed. This is in contrast to the process of diffusion which does not require energy.
The active transport across the cellular membrane is especially important for electrolytes which have physiological importance. Especially notable are the electrolytes sodium and potassium ions which are selectively pumped from one side of the cell to the other side.
This gradient in its concentration across the cellular membrane causes an electric potential on the cellular membrane which has a very important physiological role that without it we would die to the ceasing of the function of the nervous system. This ions gradient across the cellular membrane is especially important in nerve and muscle tissues.
It is important in nerve cells, for example, since we can perceive sensation by the transporting of electric signals from one neuron to another. It is also important in muscle cells. In muscles the presence of calcium ions in the cytoplasm initiates the contraction of the muscle tissue. Calcium is being continuously pumped outside the cell via ATPase induced pump. In addition calcium is also being pumped into the sarcoplasmic reticulum from the cytosol.
Protein synthesis or translational process is a very important process which occurs in cells which possess nucleus. Cells that do not have nucleus such as red blood cells are dependent on their supply of proteins from other sources outside the cell. Protein synthesis in the cell is a very important process due to the immense role that proteins play in the biology of the cell.
Proteins play a key role that is manifested by the structural proteins such as the protein collagen. In addition it is manifested as proteins which have functional role such as polypeptide hormones and enzymes. Examples of which are the hormone insulin and the enzyme carbonic anhydrase. In addition proteins can be antigentic which are proteins that are foreign to the body.