Proteins are macromolecules made up of linear chains of amino acids and composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). They also usually have small amounts of phosphorus (P) and sulfur (S). These are essential molecules in the constitution of organisms. For most of the tasks, cells require protein. Among their multiple functions, we have their role as structural components, participation in metabolic regulation, the transport of other molecules, and immune defense.
What are Amino Acids?
Amino acids are organic substances that contain at least one amino group (-NH 2 ) and at least one acid group, which is always the carboxyl group (-COOH) except in the case of taurine (which is -SO 3 H). In this way, we can establish a general structural formula for all the amino acids.
It is important to note that the carbon is asymmetric (it is attached to four different radicals) in all amino acids except glycine. All amino acids have optical activity (in a solution, they deviate the plane of polarized light to the left or the right), except for glycine. Only levorotatory amino acids, L, are part of proteins.
Another vital characteristic of amino acids is that they are amphoteric. When dissolved in aqueous water, amino acids can ionize as an acid when the pH is fundamental, as a base when the pH is acidic, or as both an acid and a base when the pH is neutral.
Classification of Amino Acids Peptides
There are numerous different amino acids in nature, but only about 20 are part of proteins; they are what we call proteinogenic. Here we will only deal with these 20 amino acids.
According to their structure, amino acids class as follows:
- Aliphatic. Alanine, valine, proline, methionine, leucine, and isoleucine
- Aromatic. Phenylalanine and tryptophan
- Basics. Histidine, arginine, and lysine.
- Acids. aspartate and glutamate.
- Without charge. Glycine, serine, threonine, cysteine, tyrosine, and Glutamine.
What are the 5 Amino Acids Proteins?
On the other hand, some amino acids are not synthesizable by the body and therefore come through the diet. These are called essential amino acids. For the human species, there are eight essential amino acids: threonine, methionine, lysine, valine, tryptophan, leucine, isoleucine, and phenylalanine. Histidine is considered necessary during growth, but not in adults.
What are Peptides?
A peptide is a molecule that results from the union of two or more amino acids (AA) through amide bonds. In peptides and proteins, these amide bonds are called peptide bonds and result from the reaction of the carboxyl group of one AA with the amino group of another, with the elimination of a water molecule. Peptides are generally considered, according to the author, to be no greater than 50 or 100 amino acids. Also, in general, a polypeptide chain is regarded as a peptide and not a protein if its molecular weight is less than 5,000 daltons.
When the peptide is less than 10 AA, it is an oligopeptide (dipeptide, tripeptide, etc.). If a peptide contains between 10 and 50 AA, it is a polypeptide. When the number of AA is higher, it is called a protein. In living beings, more than 1000 AA proteins exist.
Regardless of the length of the polypeptide chain, there will always be an unreacted NH 2 group (the amino terminus) and an unreacted COOH group (the carboxyl terminus). Each peptide or polypeptide is conventionally written from left to right, starting from the N-terminus, which has a free amino group and ending with the C-terminus, where there is a free carboxyl group. When naming an oligopeptide, the main AA is the one that retains the carboxyl group. The rest of the AAs are named substituents, starting with the AA that occupies the amino terminus. Thus, for example, a Pro-Tyr-Lys tripeptide will be called prolyl-tyrosyl-lysine.
Functions of Peptides
Among the various natural functions that peptides can develop, we can highlight:
They regulate blood pressure. An example is that the precursor protein makes the octapeptide angiotensin II hydrolysis without vasopressor activity. Another example would be bradykinin, a hypotensive nonapeptide (vasodilator activity).
Here we have numerous examples here are the most important:
Oxytocin: nonapeptide secreted by the pituitary gland. It causes uterine contraction and milk secretion by the mammary gland, facilitating the delivery and feeding of the newborn.
Vasopressin: nonapeptide that increases the reabsorption of water in the kidney (antidiuretic hormone).
Somatostatin: 14 amino acids. Inhibits the release of growth hormone
Insulin: 51 amino acids. It stimulates the absorption of glucose by the cells (decreases the presence of glucose in the blood). Insulin is the first peptide sequenced by chemical methods.
Glucagon: 29 amino acids. Its effects are the opposite of insulin’s; it helps increase blood glucose levels.
Neurotransmitters. Among the peptides that carry out these functions, we have the enkephalins (5 AAs), β-endorphin (31 AAs), and substance P (11 AAs).
Antioxidants. The role of the tripeptide glutathione is essential as a cellular antioxidant. Reduces reactive oxygen species that are toxic to the cell.
Are Peptides Proteins?
Proteins with high molecular weight biomolecules are of a linear chain of amino acids. They link by peptide bonds that remain folded to show a three-dimensional structure.
Proteins perform numerous functions in the body. They are structural proteins or proteins with biological activity generically depending on their process.
Structural proteins intervene in the constitution of tissues, organs, and cells. Examples include collagen, which is part of the skin, ligaments, tendons, bone, and matrix of various organs.
Proteins with biological activity intervene or facilitate a biochemical process in the organism. The functions here are almost innumerable, from regulating metabolic processes to participating in the defense (immune system), passing through being transport molecules for other molecules in the blood.
According to their chemical composition, proteins are two main types:
Simple. Consisting only of amino acids. Among them, we have albumins, globulins, and histones.
Conjugates. They are in the composition other different molecules in addition to amino acids. The non-amino acid part is in the prosthetic group. Among them, we have glycoproteins or mucoproteins, lipoproteins, and metalloproteins.
What is the Difference Between Amino Acids Peptides and Proteins?
To conclude talking about proteins could take us several posts to define all their functions or types, so for now, we will leave it here, keeping the idea that proteins are the molecules that carry out most of the tasks of the cells.