Proteins are a very important class of compounds for the proper functioning of the human body. They have structural as well as functional roles. Proteins are composed of chains of amino acids that are connected with each other through a chemical bond.
Amino acids have an amino group and a carboxyl group. Bonds in proteins are called peptide bonds and are formed from the bonding of the amino group of one amino acid with the carboxyl group of the other amino acid.
The strctural role of proteins in the body is exemplified by the protein collagen which is found in the connective tissue and imparts strength and stiffness to the tissue. Another example of a structural protein is the microfilaments of the cytoskeleton of the cell.
Another example of a structural protein is found in the phospholipid bilayer of the cellular membrane. These proteins have also functional role. They change conformation by a specific signal either by an electric signal or by a neurotransmitter signal.
This change in conformation of the protein can lead to either closing or openning of ion channels. Thus leading to the initiation or termination of action potential. This can lead for example to muscle contraction or relaxation.
Proteins have an important functional role in the human body. An important group of proteins are the enzymes group. Enzymes are a group of proteins which can catalyze or accelerate metabolic reactions. Without the catalyzing of biochemical reactions in the body by the enzymes we would not be able to survive.
An example of an enzyme is carbonic anhydrase which catalyzes the conversion of the bicarbonate ion to water and carbon dioxide. Therefore, carbonic anhydrase is a target for a clinical drug that inhibits its action. This drug is used to treat the medical condition called glaucoma.
Carbonic anhydrase catalyzes the formation of water in the aquous humour of the eyeball. Its inhibition leads to amelioration of the glaucoma condition. An example of such a drug is called acetazoleamide.
Another group of proteins besides the enzyme group and which also have important functional role are the hormonal proteins. Many of the hormones inside our body are proteins or polypeptides.
Aside from the steroid hormones that are secreted by the adrenal gland and the testis and the kidney other endocrine glands secrete protein hormones. An example of a protein hormone and which is secreted by the pituitary gland is antidiuretic hormone or ADH. This hormone is a polypeptide that is similar in structure to the hormone oxytocin.
ADH has an important functional role in controlling water homeostasis or the rate of secretion of water by the kidney tubules. Oxytocin and which has similar structure but different sequence of amino acids has a function related to the contraction of muscle cells of the female breast and the uterus.
Structurally speaking, proteins have four distinct structures. The primary structure of proteins is defined as the sequence of amino acids in the polypeptide chain. The secondary structure of proteins is defined by the alpha-helix and beta-sheet structures of the proteins.
The tertiary structure of proteins is defined by the folding of the protein secondary structure to a hydrophobic and hydrophilic domains. The hydrophilic part being exposed to the aquous environment while the hydrophobic part is pointing away from the aquous layer.
The quaternary structure of proteins is defined when two polypeptide chains bond to each other by S-S bonds forming a bigger polypeptide.
Proteins are synthesized in the cell based on a genetic code in the form of DNA bases which each three of them code for one amino acid. These three DNA bases are called codon. Each codon codes for one amino acid. The synthesis of the protein is done on the ribosome of the cell.
In genetic diseases protein synthesis is errored due to the genetic code being wrong. In cancer also the protein synthesis is errored due to the same reason as with the genetic diseases.
