THE BIOMOLECULE CALLED PROTEIN

Proteins are one of the four main types of biomolecules. Biomolecules principally refer to active substances in the living system. There are four distinct groups that function such that life will be impossible without them. These are Carbohydrates, Lipids, Nucleic Acids, and Proteins. Proteins are found as large complex structures in our bodies.

When there is a talk about proteins, it doesn’t always only involve food and nutrition –proteins are far more diverse than that. They are found in different forms and play many roles. In structures, they exist as the keratin in hair, skin, and nails, as collagen in bones, as myosin and actin in the muscles, as transporters of oxygen in the blood, and as antibodies in the immune system. Among other things –the list continues. Again, when in excess, proteins are converted to carbs or fat to be used for energy. A single cell contains myriads of proteins: life itself is hinged on the activities of proteins. Many diseases can be traced to defects in one protein or the other. In all, proteins are very important molecules.

?

ALPHA-AMINO CARBOXYLIC ACIDS

The big structure of protein consists of smaller monomeric units called?amino acids. Amino acids are the building blocks of proteins. They are organic compounds that contain basic alpha-amino (-NH2) and acidic carboxylic (-COOH) groups. They also all contain a side chain R group that defines the properties of each amino acid. This defining-ability is because the R group varies in constituent, size, and charge in the different amino acids.

Twenty amino acids are commonly found in proteins. They connect in various ways and numbers to create many proteins with unique functions.

FUNCTIONS OF PROTEINS??

{One}: Enzymes are proteins: Enzymes are catalysts that speed up biological reactions. Without enzymes, life processes will be too slow to be feasible. Cells contain a LOT of enzymes. And these enzymes are proteins.

(An exception to this are the RNA enzymes, Ribozymes, that have a catalytic function like proteins).

{Two}: Some hormones are proteins: Hormones are signaling molecules, they are chemical messengers that regulate development and physiological activities. They are produced from steroids or proteins.

{Three}: Immunoglobins (antibodies) are proteins: Antibodies are defensive molecules that help destroy foreign materials. They make up a good portion of the immune system.

{Four}: Receptors are protein molecules that receive signals: Signals are brought by ligands that when bound to proteins (receptors), evoke cellular changes.

{Five} Structural proteins provide resilience and plasticity: Examples are collagen and elastin found in the connective tissues.

{Six} Energy: In times of starvation, the body turns to protein as an energy source.

PROTEINS AND FOOD

Unlike carbohydrates and lipids, proteins are not stored in the body. That is, there is no reserve for currently-not-in-use proteins. Rather, there is a repeated turnover involving synthesis and breakdown. And then excesses are converted to other biomolecules.?

When proteins are consumed, the required portion of it is used in the synthesis of new protein structures, while the excess is converted to other carbohydrates and fat. In this form, they serve as an energy source or reserve.

For this reason –the absence of a reservoir –the body is in need of a regular supply of amino acids, the building block of proteins. This supply can be gotten from our meals. Protein obtained from eggs, milk, beef, and chicken are animal-based. Beans, oats, avocado, etc. provide plant-based proteins.

Lack of sufficient protein intake leads to protein deficiency, the most severe of which is Kwashiorkor. Muscle atrophy, porous bone, fatty liver disease, are also other conditions that can result from insufficient intake of proteins.

CLASSIFICATION OF AMINO ACIDS.??

Amino acids can be classified based on their R groups and essentiality. The classification of amino acids based on R groups is not rigid –this segregation slightly varies in different academic materials. Roughly, amino acids can be grouped into three groups based on their side chains. These are {i} the nonpolar and neutral amino acids, {ii} the polar and neutral amino acids, and {iii} the polar and charged amino acids.

Below is a picture of the twenty common amino acids.

Amino acids -BioNinja?

Another grouping of amino acids is based on their natural synthesis –and the absence of it –in the body. On this basis, there are three groups of amino acids. These are {i} essential amino acids, {ii} non-essential amino acids, and {iii) conditional amino acids.

Essential amino acids?are amino acids that cannot be synthesized in the body. They can only be gotten from food (or supplements). Their absence in the body?(not better functions than nonessential amino acids)?makes them essential. There are nine essential amino acids. These are Isoleucine, leucine, histidine, tryptophan, threonine, valine, phenylalanine, methionine, and lysine.

Nonessential amino acids?are those that can be synthesized in the body. They include eleven other amino acids. They all play important roles in living systems.

Conditional amino acids?are nonessential amino acids that become relevant when the body is going through physiological trauma caused by one sickness or the other. These include proline, arginine, serine, cysteine, tyrosine, glutamine, and glycine.??

?

PEPTIDE BOND (–CO –NH –)

Peptide bond (also known as amide bond) is found between amino acids. It is a bond formed by the condensation of the carboxyl group of one amino acid and the amino group of another. It also involves the removal of water.

If two molecules are involved in this condensation reaction, a dipeptide (with one peptide bond) is formed. If three amino acids are involved, it is a tripeptide with two peptide bonds. Proteins are called?polypeptides?because they contain many peptide bonds.

The peptide bond is rigid due to its partial double bond character. This conformation determines certain properties found in proteins, especially in their secondary structures.?

?

LEVEL OF PROTEIN STRUCTURE

There are four levels of protein structures. They describe the various stages of a protein’s movement from its simplest form to its folding into a more complex functional state.

The level of protein structures are:

{One} Primary structure:?The primary structure of a protein is determined by the sequence of its amino acids. This linear sequence of amino acids is a product of transcription and translation of its codes in DNA (gene).

The primary structure determines the chemical properties of that protein –a single change in the gene for one amino acid of a protein can result in a new or defective product. A good example of this is seen in sickle cell anemia where valine replaces glutamic acid. This change from a polar and charged amino acid to a nonpolar one causes deoxygenated hemoglobin to take on a sickle shape that over time results in stacking (sticking and polymerization due to lesser solubility-higher hydrophobicity) of the protein, as well as manifestations of the defect.

?

{Two} Secondary structure: The secondary structure of protein results from interactions of its amino acids via its backbones (that is the basic structure without the R groups). This interaction can form two different types of structures called?the alpha helix?and the?beta-pleated sheet. Hydrogen bonding between amino acids holds the secondary structures of protein.??

?

{Three} Tertiary structure: This is the three-dimensional structure of a protein that determines its function. It is mostly established by interactions between R groups of amino acids in the protein. Noncovalent bonds like ionic bonding, hydrogen bond, hydrophobic interaction, and Vander Waal’s forces hold this functional structure.

?

{Four} Quaternary structure: Quaternary structure refers to a protein consisting of different amino acid chains. These chains are called subunits. They can be two, three, four (like hemoglobin), or more.??

?

?

FOCUS OF NOTE:

Myriads of proteins can be found in a single cell: this large complex biomolecule plays important roles crucial to life. They are made up of monomeric amino acid units joined together by peptide bonds. And these units fold into different patterns (in different numbers and order), resulting in a large inventory of different functional protein structures. These structures act as antibodies, transporters, enzymes, signaling molecules, and more.??

References:

https://www.khanacademy.org/science/biology/macromolecules/proteins-and-amino-acids/a/introduction-to-proteins-and-amino-acids

https://www.medicalnewstoday.com/articles/196279

https://www.britannica.com/science/amino-acid