Question

Tertiary structure of protein contains which type of forces? (a) electrostatic, hydrogen bonds, van der Waals forces, dipole-dipole attractions and disulphide cross linkage (b) electrostatic, hydrogen bonds and van der Waals forces (c) electrostatic forces only (d) electrostatic as well as hydrogen bonds

Short answer

(a) electrostatic, hydrogen bonds, van der Waals forces, dipole-dipole attractions, and disulphide cross-linkages.

Step-by-step solution

Understanding Protein Tertiary Structure

The tertiary structure of a protein is its overall three-dimensional shape, which is formed by the interactions of the side chains (R groups) of the amino acids in the polypeptide chain. These interactions are crucial for the protein's stability and function.

Evaluating Interaction Types

Identify the types of chemical bonds and interactions that can stabilize the tertiary structure of proteins: electrostatic interactions (ionic bonds between charged side chains), hydrogen bonds (between polar groups), van der Waals forces (due to transient dipoles in close side chains), dipole-dipole interactions, and disulphide cross-linkages (covalent bonds between cysteine residues).

Analyzing Option (a)

Option (a) lists electrostatic interactions, hydrogen bonds, van der Waals forces, dipole-dipole attractions, and disulphide cross-linkages. All of these are known to contribute to the stability of protein tertiary structures, making this option comprehensive.

Analyzing Option (b)

Option (b) includes electrostatic interactions, hydrogen bonds, and van der Waals forces, which are significant but not exhaustive of all the forces present in tertiary structures.

Analyzing Option (c)

Option (c) suggests electrostatic forces only. This is insufficient as it does not account for hydrogen bonding or other crucial interactions like van der Waals forces and disulphide bonds.

Analyzing Option (d)

Option (d) lists electrostatic and hydrogen bonds but omits van der Waals forces and important disulphide linkages, making it incomplete.

Selecting the Best Answer

Option (a) is the most comprehensive, listing all the key forces and interactions involved in stabilizing protein tertiary structures, including electrostatic, hydrogen bonds, van der Waals forces, dipole-dipole attractions, and disulphide cross-linkages.

Key concepts

Electrostatic Interactions

Proteins are made up of long chains of amino acids, and each of these amino acids has a specific side chain, sometimes referred to as an R group. When we talk about electrostatic interactions, we're referring to the forces between charged R groups. These are also known as ionic bonds. Proteins often have side chains that are positively or negatively charged. For example, amino acids like lysine and arginine carry positive charges, while glutamate and aspartate carry negative charges.

These opposite charges attract each other, just like magnets. This ionic attraction helps to hold the protein together, contributing to its overall stability. In the complex environment of a cell, electrostatic interactions ensure that the protein maintains its correct shape.

The importance of these interactions cannot be overstated, as even a single disrupted bond can lead to changes in the protein structure, impacting its function. In essence, electrostatic interactions act as glue, keeping the proteins' intricate design in place.

Hydrogen Bonds

Hydrogen bonds are another critical component in the stability of protein tertiary structures. A hydrogen bond occurs when a hydrogen atom, covalently bonded to a highly electronegative atom like oxygen or nitrogen, is attracted to another electronegative atom within the protein. It's not as strong as a covalent bond but is very important in biological molecules.

In proteins, you often find hydrogen bonds forming between the backbone components and between the side chains. These bonds can occur repeatedly, creating a network of interactions that stabilizes the protein's three-dimensional shape. An example is the bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another.

The strength of hydrogen bonding depends on the distance and orientation between the interacting atoms. Despite the relative weakness of a single hydrogen bond, their cumulative power in proteins is significant, playing a vital role in maintaining the protein's shape necessary for its biological functions.

Van der Waals Forces

Van der Waals forces are weak interactions that occur between atoms or molecules which are very close to each other. These forces result from transient dipoles formed when electrons are not perfectly symmetrical around an atom. While individually weak, when many van der Waals interactions occur simultaneously, they can have a remarkable stabilizing influence on the protein's structure.

In the protein, these forces are generated as the side chains of amino acids come in close proximity. Even slight shifts in electron density can lead to these interactions, and they are particularly important for proteins as they fold into their compact shapes.

They help in contouring the surface of the protein, allowing it to fit perfectly into its biological niche. Although they can't hold a protein together on their own, they complement other forces like hydrogen bonds and electrostatic interactions, significantly contributing to the final stable structure of a protein.

Disulphide Cross-linkages

Disulphide cross-linkages are strong covalent bonds formed between the sulfur atoms of two cysteine amino acids, resulting in a link known as a disulphide bond. These bonds are especially critical for proteins that need to maintain stability in harsh conditions, such as those found outside a cell or in extreme environments.

When two cysteines come close during protein folding, their sulfur atoms can oxidize and form a covalent bond with each other. This bond acts like a 'molecular staple', holding parts of the protein firmly together. This reinforcement means that disulphide bonds play a crucial role in maintaining the polypeptides' three-dimensional shape.

While not all proteins have disulphide bonds, they are prevalent in extracellular proteins like antibodies and enzymes. These bonds are essential in maintaining the integrity and functionality of such proteins, preventing them from denaturing or losing their shape in fluctuating environmental conditions.