Question

Describe Hierarchal and Molten Globule models of protein folding and explain what Levinthal's paradox is.

Answer 1

Hierarchal folding model:

• the primary structure of a protein is its unique sequence of amino acid (1^o)
• secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain (2^o)
• tertiary structure is determined by interactions among various side chain (R groups) (3^o) [disulphidebond, vanderwaals interaction, the most functional structure of protein]
• quaternary structure result when a protein consists of multiple polypeptide chains (4^o) [globular protein ex-haemoglobin]

Molten globule model:

This state of a protein is an intermediate conformational state between the native and fully unfolds of the globular protein.

• The presence of native-like content of 2^o structure.
• The absence of specific tertiary structure produced by the tight packing of the amino acid side chain.
• Model for early stages of protein folding (hydrophobic collapse)

Levinthal's Paradox:

There are a large number of possible conformations present in a polypeptide chain.

it's too much difficult to search all conformational space. so it will take an astronomical length of time to find correct structure by means of a systematic search.

But it has been made easy as the folding process does not involve a series of mandatory steps between specific partially folded states, but rather a stochastic search of the many conformations accessible to a polypeptide chain.