Protein Structure and Function
Protein can be found in muscles, bones, skin, hair, and almost any other organ or tissue in the body. It is the building block of enzymes, which power many chemical reations, as well as, haemoglobin that transports oxygen in your blood.
Amino acids are the twenty-plus basic building blocks that makeup protein. Because we can't store amino acids, our systems produce them in one of two ways: from scratch or by modifying other amino acids. The essential amino acids, which include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, must be obtained from food.
Functions of Protein
Proteins are important for the execution of complex processes and for the synthesis and regeneration of DNA. Enzymes are proteins that digest food.
Proteins are linked to the creation of a number of hormones that help keep the body's components in check. Cells use surface receptors to communicate with each other and with the outside world. These receptors are composed of proteins.
Antibodies are proteins in the body that the immune system uses to repair and heal the body after foreign pathogens have been introduced. Proteins that allow cells and organs to interact.
The Structure of Protein
Peptide bonds are formed by the condensation of amino acids to form protein structures. Between the amine group of one molecule and the carboxyl group of the neighbouring molecule, a peptide bond (-CO-NH) is formed, followed by the removal of a water molecule. Otherwise, this is an amide linkage. A polypeptide chain is formed when peptide bonds are formed between more than ten amino acids. When the mass of a polypeptide chain surpasses 10000u and the number of amino acids in the chain exceeds 100, a protein is created.
What are The Four Types of Structure of Protein?
Primary Structure
The primary structure is defined as the sequence of amino acids that compose a polypeptide chain. Proteins are divided into 20 distinct amino acids. The order in which amino acids exist in a protein is known as its primary sequence.
Secondary Structure
The backbone's regular, repeating folding patterns are referred to as a protein's secondary structure. The two most common folding patterns are the alpha helix and the beta-sheet.
α – Helix: The Helix is one of the most popular ways for a polypeptide chain to generate all potential hydrogen bonds 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. The polypeptide chains formed a right-handed screw as they twisted.
β – pleated sheet: The chains of polypeptides come next to one another and are then connected by H-bonds in this manner. All peptide chains are stretched to nearly maximum extension and then arranged side by side in this structure, which is held together by intermolecular hydrogen bonds. The structure resembles the pleated folds of drapery that is why it is called a β – pleated sheet.
Tertiary Structure
The entire polypeptide chain folded into a precise 3D shape is called tertiary structure. Enzymes usually have a compact spherical tertiary structure.
Quaternary Structure
Many proteins are composed of several polypeptide chains. The quaternary structure of a protein describes how the various subunits are packed together to produce an overall structure.
More on The Topic
Proteins are large, specialized, and complex molecules that include oxygen, carbon, nitrogen, hydrogen, and sometimes sulfur. Proteins are composed of thousands of smaller units known as amino acids which are attached together to form a long chain of polypeptides (proteins).
There are a total of 20 different types of amino acids that combine together to make proteins. These amino acids are identical but have different side chains. The amino acid sequence of proteins determines the unique 3-dimensional structure of each protein and its specific function. The function of the protein in the human body is that it is required for the structure, regulation, and function of the tissues and organs of the body.
(Image will be Uploaded soon)
The structure of a protein is a 3-dimensional arrangement of amino acid residues that link up to form polypeptide chains. Proteins are polymers whose structure is formed by the link-up of several such long chains that are made from amino acid (monomer of protein) sequences. The position and property of amino acids decide the ultimate structure and function of the protein.
(Image will be Uploaded soon)
Amino acids are substituted methane, in which the alpha-carbon valencies are occupied by a carboxyl group (-COOH), amino group (-NH2), hydrogen, and a variable R-group. A variety of amino acids are present depending on the R-group, out of which 20 are used in the making of the polypeptide chain. The structure of a protein is better described by using its types.
FAQs on Protein
1. What are proteins and what are their basic building blocks?
Proteins are large, complex macromolecules essential for nearly all biological processes. They are polymers, meaning they are made of long chains of repeating smaller units. The basic building blocks of proteins are called amino acids. A specific sequence of these amino acids linked together forms a polypeptide, which then folds into a functional protein.
2. How do environmental factors like temperature and pH affect the structure and function of a protein?
A protein's function is directly dependent on its precise three-dimensional structure. Environmental factors can disrupt this structure in a process called denaturation, rendering the protein non-functional.
- Temperature: High temperatures increase the kinetic energy within the molecule, breaking the weak hydrogen bonds and other non-covalent interactions that maintain the protein's folded shape.
- pH: Extreme changes in acidity or alkalinity alter the ionic charges on the amino acid side chains, which disrupts the electrostatic bonds and hydrogen bonds, causing the protein to unfold.
3. What are some important examples of proteins and their specific functions in the human body?
Proteins perform a vast array of functions. Key examples based on their roles include:
- Enzymes: Pepsin and Trypsin act as biological catalysts that speed up the digestion of food.
- Transport: Haemoglobin, found in red blood cells, transports oxygen from the lungs to the rest of the body.
- Structural Support: Collagen provides strength and structure to skin, bones, and tendons, while Keratin forms hair and nails.
- Hormonal Regulation: Insulin is a protein hormone that regulates blood glucose levels.
- Immunity: Antibodies (Immunoglobulins) are proteins that identify and neutralize foreign invaders like bacteria and viruses.
4. Can you explain the four levels of protein structure and why each level is important?
The complex shape of a protein is understood by studying its structure at four distinct levels:
- Primary Structure: This is the unique linear sequence of amino acids in a polypeptide chain. This sequence is determined by an organism's DNA and is critical as it dictates all subsequent levels of folding.
- Secondary Structure: This refers to the local, repetitive folding of the polypeptide chain into structures like the α-helix (a spiral) and β-pleated sheet. These shapes are stabilised by hydrogen bonds.
- Tertiary Structure: This is the overall three-dimensional shape of a single polypeptide chain, resulting from interactions between the amino acid side chains (R-groups). The tertiary structure is essential for the protein's specific biological function.
- Quaternary Structure: This level describes the arrangement of multiple polypeptide chains, or subunits, to form a single, larger functional protein complex. Haemoglobin is a classic example, made of four subunits.
5. How is a peptide bond formed, and why is it crucial for the primary structure of proteins?
A peptide bond is the covalent bond that links amino acids together. It is formed through a dehydration synthesis reaction, where the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another, releasing a molecule of water. This bond is fundamentally crucial because it forms the strong backbone of the polypeptide chain, which defines the primary structure of a protein. The sequence and number of amino acids joined by these bonds determine the protein's identity and its final folded shape.
6. Why are proteins considered essential macromolecules for life?
Proteins are considered essential macromolecules because of their immense structural and functional diversity, which is unmatched by other biological molecules. They are the primary 'workhorses' of the cell, involved in virtually every task required for life. Their importance includes catalysing metabolic reactions, providing structural frameworks for cells and tissues, transporting vital substances, regulating cellular processes, and defending the body against disease. Without proteins, these fundamental life-sustaining processes could not occur.
7. What is the difference between a globular and a fibrous protein? Provide an example of each.
Globular and fibrous proteins are two major classes categorised by their shape, solubility, and function:
- Globular Proteins: These proteins are folded into a compact, spherical or 'globular' shape. They are typically soluble in water and have dynamic functions. An excellent example is myoglobin, which transports oxygen within muscle cells.
- Fibrous Proteins: These proteins have a long, linear, and rope-like structure. They are generally insoluble in water and play a structural or protective role, providing strength and elasticity. A key example is collagen, the most abundant protein in mammals, found in skin and bones.
8. What happens during the denaturation of a protein, and is this process reversible?
Denaturation is the process where a protein loses its native secondary and tertiary structures. This unfolding is caused by exposure to external stressors like heat, extreme pH, or certain chemicals. While the primary sequence of amino acids remains intact, the loss of its specific 3D shape means the protein loses its biological activity. In some instances, if the denaturing agent is removed gently, the protein may refold into its functional shape. This reversal is called renaturation. However, denaturation is often irreversible, especially if the exposure was harsh or prolonged, like when cooking an egg.
