Basic unit of protein and its function

The word protein is derived from Greek word, “proteios” which means primary. As the name shows, the proteins are of paramount importance for biological systems. Proteins are biochemical molecules consisting of polypeptides joined by peptide bonds between the amino and carboxyl groups of amino acid residues.

Proteins are made up of hundreds or thousands of smaller units known as amino acids. Most organisms use 20 naturally-occurring amino acids to build proteins. The linear sequence of the amino acids in a protein is dictated by the sequence of the nucleotides in an organisms’ genetic code. Amino acids can combine to form long linear chains known as polypeptides. Each type of polypeptide chain has a unique amino acid sequence.

The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function such as catalysis of biochemical reactions, mechanical support and immune protection, movement, transport of ligand, transmits nerve impulses, and control growth and differentiation.

The proteins function to regulate specific steps in metabolism – one step, one protein. Hence, many proteins are needed.

The polypeptide must fold into a specific three-dimensional structure before it can perform its biological functions. The function of all proteins depends on their ability to specifically interact with other molecules. Such specificity is possible because polypeptides with different amino acid sequences fold into different tertiary structures.

Proteins are not entirely rigid molecules. They undergo conformational changes upon ligand binding. Each kind of protein evolved to interact with a specific molecule or ligand. For example, transport proteins (such as hemoglobin) bind to specific ligands (in this case oxygen) and transport the ligand to a site where it is needed. Hemoglobin, the transporter of oxygen is a tetrameric protein (alpha 2, beta 2), with each monomer having a heme unit. Binding of oxygen to one heme facilitates oxygen binding by other subunits.

Storage proteins such as myoglobin, another oxygen-binding protein, allow the cell to store higher concentrations of the ligand than otherwise would be possible.

Catalytic proteins— the enzymes—convert the ligands into other molecules. They act as biochemical catalysts. The first step in enzymatic catalysis is the binding of the enzyme to the substrate. This, in turn, depends on the structural conformation of the active site of the enzyme, which is precisely oriented for substrate binding

Many proteins have structural or mechanical functions. Structural proteins interact with specific molecules, often endowing the bound molecules with special biological properties. For instance, one class of proteins, the histones, binds to DNA to form compact nucleoprotein structures called nucleosomes, while a second class of proteins combines with RNA to form the ribonucleoprotein complex known as the ribosome.

Structural proteins collagen is the most abundant protein in mammals and is the main fibrous component of skin, bone, tendon, cartilage and teeth.

Proteins are also important in cell signaling, immune responses, cell adhesion, and the cell cycle.
Basic unit of protein and its function

 

Structure of protein

In 1960, the British biochemist John Kendrew used a method called ‘X-ray diffraction’ to photograph myoglobin at a 2 A resolution and became the first man to determine the three-dimensional structure of a protein.

The basic structure common to all proteins is the peptide linkage which is formed by condensation the carboxyl group of one of amino acid with the amino group of another.

In this way chains are created, which contains only 3 amino acids, to complex polymers of 1000 or more. At physiological temperatures in aqueous solution, the polypeptide chains of proteins fold into a form that in most cases is globular.

The sequence in which amino acids are arranged in the peptide chain is known as the primary structure of the molecule. In biochemistry, this is always given starting with the N-terminal and ending with the C-terminal amino acid, because this is the order in which amino acids are added during protein synthesis in the cells.

The amino acid chain is the primary and central component of the protein, but not necessarily the only component. Some protein may include other atoms or small molecules which are required for their function and. or stability. The proper sequence of amino acids tends to be a critical factor in protein function.

Protein molecules serve as some of the major structural elements of living system. This function depends on specific association of protein subunits with themselves as well as with other proteins, carbohydrates and so on, enabling even complex systems like actin fibril to assemble spontaneously.
Structure of protein

The meaning of carbohydrate

Carbohydrates is the most widely distributed, naturally occurring organic compounds on Earth.

Carbohydrates are major nutrients which supply the body with energy and of which billions of tons are produced every year though photosynthesis by plants and cyanobacteria.

The term carbohydrate literally means ‘carbon + water’ and partially describe its chemical makeup.

It was found in the nineteenth century that carbohydrates in general have formula Cn(H2O)n. They were therefore thought to be hydrates of carbon and hence were called carbohydrates.

Later it was found that carbohydrates in fact contain hydroxyl groups and carbonyl groups and are polyhydroxy aldehydes or ketones.

Carbohydrate also called saccharides an are usually divided onto three groups: monosaccharides, disaccharides and polysaccharides. Saccharides was from Greek word ‘sakcharon’ meaning sugar.

The term ‘monosaccharide’ refers to a carbohydrate derivative possessing a single carbon chain: ‘disaccharide’ and ‘trisaccharide’ refer to molecules containing two or three such monosaccharides units joined together by acetal or ketal linkages.

Carbohydrates posses a large number of functionalities, at least one carbonyl and several hydroxyl per monosaccharide and often carry kinds of functional groups.
The meaning of carbohydrate