11.16. Proteins in aqueous solution fold to unique three-dimensional structures atambient conditions. However, they also have a first-order-like transition to astate of less-structured, floppy configurations that can be accomplished in anumber of ways. The most common is by increasing T past the folding tempera-ture at ambient pressure. They can also be unfolded by extreme compression,cooling, and expansion into the negative-pressure regime, at least in theoryFigure 11.8 gives a schematic of the "phase" behavior and these four mechanismsof unfolding.(a) For each mechanism, indicate the signs of the volume and entropy changesassociated with the folded-to-unfolded transition, namely AV VunfoldedVfolded and AS Sunfolded SfoldedFigure 11.8. Proteins can exist in folded andunfolded states depending on the pressure andtemperature. The gray line denotes the boundarybetween the two, called the folding curve. Theindicates ambient conditions.compressionfoldedheatcold-Tunfoldedexpansion/stretching (b) Explain why the cooling and stretching mechanisms might be difficultor impossible to realize in an experiment. Hint: what would happen if thesolution contained no proteins?

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Asked Oct 24, 2019
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This problem is (11.16) from a book  "Thermodynamics and Statistical Mechanics An Integrated Approach by M. Scott Shell"

11.16. Proteins in aqueous solution fold to unique three-dimensional structures at
ambient conditions. However, they also have a first-order-like transition to a
state of less-structured, floppy configurations that can be accomplished in a
number of ways. The most common is by increasing T past the folding tempera-
ture at ambient pressure. They can also be unfolded by extreme compression,
cooling, and expansion into the negative-pressure regime, at least in theory
Figure 11.8 gives a schematic of the "phase" behavior and these four mechanisms
of unfolding.
(a) For each mechanism, indicate the signs of the volume and entropy changes
associated with the folded-to-unfolded transition, namely AV Vunfolded
Vfolded and AS Sunfolded Sfolded
Figure 11.8. Proteins can exist in folded and
unfolded states depending on the pressure and
temperature. The gray line denotes the boundary
between the two, called the folding curve. The
indicates ambient conditions.
compression
folded
heat
cold
-T
unfolded
expansion/stretching
help_outline

Image Transcriptionclose

11.16. Proteins in aqueous solution fold to unique three-dimensional structures at ambient conditions. However, they also have a first-order-like transition to a state of less-structured, floppy configurations that can be accomplished in a number of ways. The most common is by increasing T past the folding tempera- ture at ambient pressure. They can also be unfolded by extreme compression, cooling, and expansion into the negative-pressure regime, at least in theory Figure 11.8 gives a schematic of the "phase" behavior and these four mechanisms of unfolding. (a) For each mechanism, indicate the signs of the volume and entropy changes associated with the folded-to-unfolded transition, namely AV Vunfolded Vfolded and AS Sunfolded Sfolded Figure 11.8. Proteins can exist in folded and unfolded states depending on the pressure and temperature. The gray line denotes the boundary between the two, called the folding curve. The indicates ambient conditions. compression folded heat cold -T unfolded expansion/stretching

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(b) Explain why the cooling and stretching mechanisms might be difficult
or impossible to realize in an experiment. Hint: what would happen if the
solution contained no proteins?
help_outline

Image Transcriptionclose

(b) Explain why the cooling and stretching mechanisms might be difficult or impossible to realize in an experiment. Hint: what would happen if the solution contained no proteins?

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Expert Answer

Step 1

(a) Proteins in aqueous solution become larger in the size due to accumulation of fluid therefore proteins in aqueous solution fold to unique three-dimensional structure at ambient conditions.

Proteins structure changes from structured to less structured, floppy configuration that can be accomplished in a number of ways.

 

Step 2

Folding and unfolding of protein is due to change in structure with change in temperature and pressure.

As the temperature is increased, protein becomes less viscous, therefore volume will increase.

In folded structure molecules are arranged so closely which results more viscous solution and volume is less than that of unfolded structure.

Therefore, change in volume associated with the folded to unfolded transition is positive which is shown below:

>V
unfolded
'folded
AV=(Vunfolded-Vfolded) >
AV>0
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>V unfolded 'folded AV=(Vunfolded-Vfolded) > AV>0

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Step 3

Entropy is thermodynamic property which describes randomness of system. In case of folded structure molecules are well arranged while in case of unfolded structure molecules are randomly arranged. Therefore...

'unfolded
folded
AS=(S
dd)>0
-S
unfolded
folded
AS>0
help_outline

Image Transcriptionclose

'unfolded folded AS=(S dd)>0 -S unfolded folded AS>0

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