Question

Find a willing friend or family member (who may or may not have a biology background) and describe the forces responsible for the primary, secondary, tertiary, and quaternary structures of a functional protein and explain how each higher structural level depends on the preceding level. If your partner does not have a biology background, describe this concept in a way that makes sense to them (diagrams may help).

Answer 1

Primary structure

It is the simplest sequence arrangement of amino acids in a polypeptide chain. Here carboxyl of every amino acid is adjacent to one another. They are combined through a formation of peptide bond as a result of dehydration reaction. Bond is planar and do not rotate freely due to double bond character. This limit in rotation of bond is due to steric hindrance.

It only involve covalent bond linking

Secondary structure –

Nest level of protein which shows a local folded structure within a polypeptide because of the interactions of of atoms in the backbone. Here, amino acids can rotate around the bond formed within which resulted in the formation of secondary structures – alpha helix and beta pleated sheets.

Alpha helix – polypeptide chain show a coiled spring structure.this is stabilized by hydrogen bonds between carboxyl and amine hydrogen.third causes a pattern of pulling of polypeptide chain into curled ribbon like structure- helix.

Beta pleated sheets – in this PP folds back to itself and so that the strands appear side by side, held together by hydrogen bonding and resulting into a very rigid structure. This folding is done in either parallel or anti parallel manner forming a sheet like structure held together by hydrogen bonds. factors responsible for this structure are – steric hindrance and charge repulsion.

Tertiary structure

This is the 3D structure of polypeptide chain and is due to interactions b/w R group of amino acids that make the protein.interactrion involved in forming this structure are –hydrogen bonding, dipole – dipole interaction, ionic bonding , and londen dispersion forces.

Charges repel with opposite charges forming ionic bonds

R group forms H bonds and dipole dipole interactions

There are hydrophobic interactions also involved – amino acid with hydrophic R group cluster inside the structure leaving the hydrophilic AA outside.

Another – Disulfide bond that contribute in tertiary structure – between sulfur contain side chains of cystein and provide protection to the whole polypeptide structure.

This 3D arrangement include all other structure of polypeptide like alpha helix and beta sheets. Al the weak forces of secondary structure contribute to the formation of tertiary structure.

Quaternary structure –

It is made up of multiple polypeptide chain.

All the primary structures come together in different polypeptide chains and results in a tertiary structure of protein. It constitute the same interactions as tertiary structure.that is mostly weak interactions.