Food and Nutrition: Protein

Proteins are one of the vital nutrients used for energy production in the body. The other nutrients include carbohydrates and vitamins. Foods such as meat, eggs, dairy, and fish are great protein sources. Understanding the biochemistry of proteins is crucial as it enforces their importance in development, growth, and tissue repair. Moreover, proteins are also components of various body parts such as hair, skin, muscles, and bones. Approximately one-fifth of the body’s total weight is protein. Centered on mastering the biochemical composition of proteins, the following Food and Nutrition: Protein elaborate on the building blocks of proteins, protein structure, classification, and much more.

Basics of what is Food and Nutrition: Proteins and protein definition. 

The biochemical definition of proteins is macromolecules containing a backbone formed by amino acid polymerisation in a polyamide structure. Their basic repeating units are amino acids joined by peptide bonds. There are 300 identified amino acids in nature. However, only 20 amino acids are coded by DNA and present in body proteins. These are known as common amino acids. 

Amino acids.

Amino acids are the primary precursors of proteins. Understanding amino acids helps students build their knowledge in protein structure and cell functions. There are more than 300 amino acids in nature. However, only twenty amino acids are the building blocks of human cells. Amino acids focus on their chemical nature, classification, and properties.

There are six major categories of amino acids based on their side chains. These include aliphatic, basic, acidic, sulphated, hydroxyl, and aromatic amino acids. Furthermore, amino acids can be classified according to their nutritional value. There are essential, non-essential, and semi-essential amino acids. Amino acids exhibit properties such as optical isomerism, charge, buffering action, and UV light absorption. 

Peptides and Protein basics

Peptides are two or more amino acids linked by a peptide bond. Peptide bonds form by a reaction between the carboxyl group of one amino acid and the α-amino group of another amino acid leading to the loss of a water molecule. They are covalent bonds. Hydrolysis is the process required for the breakdown of peptide bonds. Peptides and proteins have N- and C- terminals.

Proteins have many biological functions. These encompass gaseous transport, immune defence, and the contraction of muscles. They also constitute molecules including hormones, plasma proteins, and immunoglobulins. Moreover, proteins are classified into simple, conjugated, and derived proteins. This classification is based on their composition. Conjugated proteins are further divided into lipoproteins, glycoproteins, phosphoproteins, metalloproteins, and nucleoproteins. There are also globular and fibrous proteins. Globular proteins include myoglobin and haemoglobin, while fibrous proteins are keratin, collagen, and elastin.

Protein structure

The linear arrangement of amino acids is unstable. Therefore, proteins fold into structures known as stable conformations. The formation of a stable conformation occurs in multiple stages categorised into four protein structures.

The protein’s primary structure entails the linear sequence of amino acids as a polypeptide chain. Bonds involved in the primary structure are covalent, including peptide and disulphide bonds. Frederick Sanger pioneered the sequencing of primary structures. He was the first scientist to detail the amino acid sequence of insulin. Protein folding occurs to form the secondary structure.

Moreover, the secondary structure of proteins can be an α-helix or a β-pleated sheet. The α-helix structure is a winding molecule with a backbone stabilised by intrachain hydrogen bonds and peptide bonds. Amino acids proline and glycine disrupt this conformation. Furthermore, the β-pleated sheets can present in parallel or antiparallel configurations. Glycine and proline are the predominant amino acid residues occurring in β-pleated sheets of globular proteins. Watson and Crick proposed the α-helix and β-pleated sheet conformations.

Several elements stabilise the tertiary structure of proteins. These are non-covalent bonds such as electrostatic, hydrogen, hydrophobic, and Van der Waals forces. Finally, the final conformation is achieved due to increased folding forming the quaternary structure. Forces that maintain these structures include hydrophobic interactions, hydrogen bonds, electrostatic bonds, Van der Waals forces, and disulphide bridges.

Protein denaturation

Denaturation involves the physical and chemical alteration of proteins. A protein that undergoes denaturation has the following properties: unfolded polypeptide chain, loss of biological function, loss of secondary structure, decreased solubility, increased chemical reactivity, and increased susceptibility to enzyme action.

Various factors trigger protein denaturation. These include high temperature, extremely acidic or alkaline pH, exposure to UV radiation, concentrated urea, detergents, and heavy metals. Furthermore, if these factors are removed or controlled, the protein retains its original structure because denaturation is irreversible. 

Conclusion:

The answer to the question ‘what is food and nutrition?’ has greatly expanded over the years. It is essential to understand the various nutrients to maintain a balanced diet. As a major nutrient, proteins have numerous functions within our bodies ranging from the molecular level to our organ function. It is also regarded as the building block of life because it contributes to the make-up of biological molecules and the preservation of the body structure. Moreover, it is important to develop our knowledge of key proteins such as haemoglobin. An in-depth understanding of haemoglobin promotes advancements in haematology and the treatment of blood disorders.