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Exposure of native protein to heat leads to partial denaturation of the protein due to breaking of-

a. S-S bonds

b. H-bonds

c. Hydrophobic interactions

d. Peptide bonds

After a bit of surface googling I understand peptide bonds are not broken in the process of denaturation and di-sulphide bonds are not broken either (by heat) but by reducers like $\beta$- Mercaptoethanol. These reducers are added in experiments to ensure that the bonds which contribute largely to the tertiary structure are broken.

So either H-bonds or hydrophobic interactions are affected. I cannot make out which one would be the most affected/first one to be affected since the question says partial denaturation, meaning, it was not heated for long.

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If you think about the boiling of water, I'm sure you can understand that heat breaks hydrogen bonds. Next consider that the hydrophobic effect is driven entropically and so, by the equation $\Delta G=\Delta H-T\Delta S$, its strength increases with temperature (to a point). See here and here for further explanation. Also, this paper for a more empirical view.

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    $\begingroup$ So as the temp. increases the hydrophobic interactions become stronger /are favoured until it is high enough to be disturbed. In the latter is it due to high KE that the hydrophobes are unable to maintain their interaction(closeness)? $\endgroup$ – Tyto alba May 4 '17 at 19:06
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    $\begingroup$ @Tytoalba Thanks, I'll add the link (and some others) to the answer. I don't like some of their wording, but overall it's pretty intuitive. I think the first link should answer your question in the comment. $\endgroup$ – canadianer May 4 '17 at 19:34
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Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein. When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein. During denaturation secondary and tertiary structures are destroyed but 1º structure remains intact. The coagulation of egg white on boiling is a common example of denaturation. Another example is curdling of milk which is caused due to the formation of lactic acid by the bacteria present in milk.

According to the above paragraph, denaturation occurs due to disruption of hydrogen bonds. The answer should be option (B). Note that the energy of hydrogen bonds are 3 - 10kcal/mol. Therefore, hydrogen bonds can be broken and formed easily. You can imagine the process of replication, transcription, etc. where H-bonds are broken and formed easily.

NCERT XII CHEMISTRY (PART II) Chp.Biomolecules 14.2.4 Pg. 141 of that PDF, but in actual book Pg. 416

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    $\begingroup$ Thank you :) for putting an effort at writing an answer. $\endgroup$ – Tyto alba May 4 '17 at 19:09
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    $\begingroup$ It is my first answer on this site and you are welcome. $\endgroup$ – San May 4 '17 at 19:10

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