The major difference between a protein molecule in its native stateand in its denatured state lies in the number of conformations avail-able. To a first approximation, the native, folded state can be thoughtto have one conformation. The unfolded state can be estimated tohave three possible orientations about each bond between residues.(a) For a protein of 100 residues, estimate the entropy change permole upon denaturation.(b) What must be the enthalpy change accompanying denaturationto allow the protein to be half-denatured at 50 °C?(c) Will the fraction denatured increase or decrease with increasingtemperature?

Proteins are macromolecules formed by amino acids. A total of 20 different amino acids exist in…

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Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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The major difference between a protein molecule in its native state and inits denatured state lies in the number of conformations available. To a firstapproximation, the native, folded state can be thought to have one conformation. The unfolded state can be estimated to have three possible orientations about each bond between residues.(a) For a protein of 100 residues, estimate the entropy change per moleupon denaturation.(b) What must be the enthalpy change accompanying denaturation to allow the protein to be half-denatured at 50 °C?(c) Will the fraction denatured increase or decrease with increasingtemperature?
The major difference between a protein molecule in its native state and in its denatured state lies in the number of conformations available. To a first ap- proximation, the native, folded state can be thought to have one conforma- tion. The unfolded state can be estimated to have three possible orientations about cach bond between residues. (a) For a protein of 100 residues, estimate the entropy change per mole upon denaturation. (b) What must be the enthalpy change accompanying denaturation to allow the protein to be half-denatured at 50 °C? (c) Will the fraction denatured increase or decrease with increasing temperature?
Assume that some protein molecule, in its folded native state, has onefavored conformation. But when it is denatured, it becomes a “random coil,” with many possible conformations.(a) If we only consider the change in entropy for the protein, what mustbe the sign of ΔS for the change: native → denatured? (Note: As suggestedin the next problem, this does not include solvent effects, which also make significant contributions to ΔS.)(b) How will the contribution of ΔS for native → denatured affect thefavorability of the process? What apparent requirement does this imposeon ΔH if proteins are to be stable structures?
Which intermolecular forces are important in acetic acid, CH3 –(C=0)-oh? A particular amino acid contains a- CHNH3+ group. Is this amino acid more likely to be found on the inside or the outside of the folded protein? Briefly explain. The addition of ethanol, CH3CHOH, t an aqueous solution lowers the surface tension of the solution. Predict whether adding ethanol to an aqueous protein solution will tend to stabilize or unfold the protein. Briefly explain.
Consider a small protein containing 101 amino acid residues. The proteinbackbone will have 200 bonds about which rotation can occur. Assume thatthree orientations are possible about each of these bonds.(a) Based on these assumptions, about how many random-coil conformationswill be possible for this protein?(b) The estimate obtained in (a) is surely too large. Give one reason why.
Consider a protein in which a negatively charged glutamic acid side chain(pKa = 4.2) makes a salt bridge (ion–ion interaction) with a positively charged histidine side chain (pKa = 6.5).(a) Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.0 to pH = 7.5?(b) Justify your answer with calculations of partial charges on these aminoacid side chains.
Consider a protein in which a negatively charged glutamic acid side chain (pKa = 4.2) makes a salt bridge (ion–ion interaction) with a positively charged histidine side chain (pKa = 6.5). (a) Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.0 to pH = 7.5? (b) Justify your answer with calculations of partial charges on these amino acid side chains.
Assume that some protein molecule, in its folded native state, has one favored conformation. But when it is denatured, it becomes a “random coil,” with many possible conformations. (a) If we only consider the change in entropy for the protein, what must be the sign of ∆S for the change: native → denatured? (Note: As suggested in the next problem, this does not include solvent effects, which also make significant contributions to ∆S.) (b) How will the contribution of ∆S for native → denatured affect the favorability of the process? What apparent requirement does this impose on ∆H if proteins are to be stable structures?
The dissociation constant, Kd for a complex between protein A and protein B is 4.1 μM. If the two proteins are mixed together at initial concentrations of [A]= 0.025 μM and [B] = 4.7 μM, calculate (a) the equilibrium concentrations of A, B, and AB (the dimer formed by A and B) (b) the percentage of A bound to B
Globular proteins with multiple disulfide bonds must be heated longer and at higher temperature to denature them. Bovinepancreatic trypsin inhibitor (BPTI), having 58 amino acids in a single chain and 3 disulfide linkages, loses its catalytic activity whenheated at nearly 90°C for 5-10 minutes. Explain the molecular basis of this observed thermal property of BPTI relative to the nativestructure and function of the protein.
. Assume that some protein molecule, in its folded native state, has one favored conformation. But, when it is denatured, it becomes a "random coil," with many possible conformations. (a) What must be the sign of AS for the change: native → denatured? (b) How will the contribution of AS for native → denatured affect the favorability of the process? What apparent requirement does this impose on AH if proteins are to be stable structures?
Peptides and small proteins fold spontaneously in aqueous solution at room temperature. Thus, for a small protein in water, we can say ΔG FOLD < 0. Denoting the unfolded protein as Unf and the folded protein as Fld, we can write the following equation:Unf(aq)--DELTA G FOLD----> Fld(aq)Considering the transition from the unfolded state (in which there are many possible conformations) to the folded state (only one conformation), there is clearly a decrease in the entropy of the protein. However, protein folding is (correctly) described as an entropically driven process.a) Resolve this apparent paradox by identifying the enthalpy (ΔH) and entropy (−TΔS)components involved in protein…

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