Quaternary Structure of Proteins: Muscles, bones, skin, hair, and practically every other organ or tissue in the body contain protein. It is a component of enzymes, which fuel numerous chemical reactions, as well as haemoglobin, which carries oxygen in the blood.
Protein is made up of amino acids, which are the twenty-plus fundamental building blocks. Because humans can’t store amino acids, our bodies make them either from scratch or by altering other amino acids. Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine are all necessary amino acids that must be acquired from the diet.
Proteins are required for the completion of complicated processes as well as the synthesis and regeneration of DNA. Enzymes are proteins that aid in the digestion of food.
Proteins are connected to the production of a number of hormones that aid in the regulation of the body’s components. Surface receptors allow cells to communicate with one another and with the outside world. Proteins make up these receptors.
Antibodies are proteins in the body that the immune system employs to mend and heal the body after it has been exposed to foreign infections. Proteins allow cells and organs to communicate with one another.
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Peptide bonds are created when amino acids combine to form protein structures. A peptide bond (-CO-NH) is created between the amine group of one molecule and the carboxyl group of the neighboring molecule, followed by the elimination of a water molecule. If not, this is an amide connection. When peptide bonds between more than 10 amino acids occur, a polypeptide chain is produced. A protein is formed when the mass of a polypeptide chain reaches 10000u and the number of amino acids in the chain exceeds 100.
Proteins have four levels of structure:
The primary structure of a polypeptide chain is defined as the sequence of amino acids. Proteins are classified into 20 different amino acids. The fundamental sequence of amino acids in a protein is the order in which they appear.
The regular, recurring folding patterns of the backbone are referred to as a protein’s secondary structure. The alpha-helix and the beta-sheet are the two most prevalent folding patterns.
α– Helix: One of the most common ways for a polypeptide chain to produce all available hydrogen bonds is by twisting into a right-handed screw and hydrogen-bonding the -NH group of each amino acid residue to the -CO of the adjacent helix turn. As the polypeptide chains twisted, they produced a right-handed screw.
β– pleated sheet: Polypeptide chains come adjacent to one another and are joined by H-bonds in this manner. All of the peptide chains are stretched to nearly their maximum extent before being stacked side by side in this structure, which is kept together by intermolecular hydrogen bonds. The pleated folds of draperies are reminiscent of the structure, which is why it is termed a β- pleated sheet.
Tertiary structure refers to the whole polypeptide chain folded into a precise 3D form. Enzymes have a tertiary structure that is compact and spherical.
Many proteins are made up of several polypeptide chains. A protein’s quaternary structure outlines how its many subunits are packed together to form an overall structure.
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A protein’s quaternary structure is the connection of multiple protein chains or subunits into a densely packed configuration. Each component has a distinct primary, secondary, and tertiary structure. Hydrogen bonds and van der Waals forces between nonpolar side chains hold the subunits together.
For the complete protein to function effectively, the subunits of a quaternary structure must be precisely organized. Any change in the structure of the subunits or how they are linked produces significant changes in biological activity.
The quantity and order of numerous folded protein subunits in a multi-subunit complex is described by protein quaternary structure. Organizations ranging from simple dimers to massive homo-oligomers and complexes with a fixed or variable number of subunits are included. Unlike the previous three levels of protein structure, the quaternary structure does not exist in all proteins since some proteins act as single units. Protein quaternary structure can also refer to protein-nucleic acid and other cofactor biomolecular complexes.
Many proteins are made up of several polypeptide chains. The quantity and order of protein subunits in relation to one another is referred to as the quaternary structure. Haemoglobin, DNA polymerase, ribosomes, antibodies, and ion channels are all examples of proteins possessing quaternary structure.
Enzymes made up of subunits with different roles are sometimes referred to as holoenzymes, with certain components referred to as regulatory subunits and the functional core referred to as the catalytic subunit. Other assemblies, known as multiprotein complexes, also have a quaternary structure. Nucleosomes and microtubules are two examples. Changes in quaternary structure can arise as a result of conformational changes within individual subunits or reorientation of the subunits relative to one another. Many proteins are regulated and execute their physiological functions as a result of such modifications, which underpin cooperativity and allostery in “multimeric” enzymes.
The temperature has a big influence on protein. Temperature changes denature proteins and alter their structure. The amino acid sequence in protein structure is unaffected by temperature, but the folding of the three-dimensional polypeptide chain is. Temperature disrupts the non-polar hydrophobic interaction.
Hemoglobin is a protein found in human blood that transports oxygen from the lungs to the tissues of the body. Proteins are formed by linking amino acids into polypeptide chains.
Environmental changes that can affect proteins include heat in the presence and absence of carbohydrates, pH variations (particularly alkaline), and exposure to oxidative conditions, including those induced by light and those caused by oxidizing lipids.