MBB 222 Lecture Notes - Lecture 6: Protein Folding, Hydrogen Bond, Chemical Potential

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browncricket987

20 Dec 2018

School

Simon Fraser University

Department

Molec Biol & Biochem

Course

MBB 222

Professor

Adam Barlev

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Document Summary

G tells us nothing about the rate at which a reaction will occur (!) e. g. , carbon (diamond) carbon (graphite) ; g = -2. 88 kj/mol. Protein folding also optimizes weak interactions (electrostatic, van der waals, h-bonding), which is enthalpically favourable, h<0. G is influenced by the characteristics of the reacting molecules, temperature, pressure, and, for biological systems, ph; it is also influenced by the concentrations of reactants and products. Standard free energy change g" is calculated for a reaction that proceeds under the conditions shown below, the standard state conditions for biochemistry: P = 1 atm ph = 7. 0 ([h+] = 10-7 m); [h2o] = 55. 5 m concentration = 1 m for reactants and products. G" represents the chemical potential with respect to the standard state it is the force driving the reaction from its initial state of 1 m reactants, 1 m products to its equilibrium state. G" is a constant for a given reaction.

Related Questions

Some proteins, once folded âassociateâ to form higher order structures (i.e., quaternary structure). Within these structures the single protein chain is known as a âsubunitâ (not to be confused with a protein domain). If two identical protein chains fold and associate, the quaternary structure is named âhomodimerâ (and the individual subunits are sometimes referred to as âmonomersâ); for three âhomotrimerâ and so on. If, on the other hand, the two protein chains that associate have different primary structures, the quaternary structure is named âheterodimerâ. Using the dimer as an example, we know that the respective regions of the protein subunit surfaces that are interfaced, are responsible for the âfavorable energy of interactionâ which stabilizes the dimeric protein complex.

(a). Although, noncovalent bonding interactions are used both for stabilization of the folded protein molecule and its dimerization, the contribution of the âhydrophobic effectâ to chain folding is significantly greater than its contribution to subunit association. Define the âhydrophobic effectâ and explain why you would expect it to have a more pronounced role in chain folding compared to dimerization of the folded molecules.

(b) As the protein chain folds to the native structure, it loses entropy. Upon dimerization, more protein entropy is lost. Compare and contrast the source of protein entropy loss, which occurs with folding, with that which occurs with dimerization.

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MBB 222 Lecture Notes - Lecture 6: Protein Folding, Hydrogen Bond, Chemical Potential

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