Download lesson-13-protein-denaturation-handout

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The three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of
amino acids within the molecule. Most of these bonds and interactions are relatively weak and they can be
disrupted or broken. This results in a change to the conformation of the protein, which is called denaturation.
A denatured protein does not normally return to its former structure – the denaturation is permanent. Soluble
proteins often become insoluble and form a precipitate. This is due to the hydrophobic R groups in the centre of
the molecule becoming exposed to the water around by the change in conformation.
Heat can cause denaturation because it causes vibrations within the molecule that can break intermolecular
bonds or interactions. Proteins vary in their heat tolerance. Some microorganisms that live in volcanic springs or
in hot water near geothermal vents have proteins that are not denatured by temperatures of 80 °C or higher. The
best known example is DNA polymerase from Thermus aquaticus, a prokaryote that was discovered in hot
springs in Yellowstone National Park. It works best at 80 °C and because of this it is widely used in
biotechnology. Nevertheless, heat causes denaturation of most proteins at much lower temperatures.
Extremes of pH, both acidic and alkaline, can cause denaturation. This is because charges on R groups are
changed, breaking ionic bonds within the protein or causing new ionic bonds to form. As with heat, the threedimensional structure of the protein is altered and proteins that have been dissolved in water often become
insoluble. There are exceptions: the contents of the stomach are normally acidic, with a pH as low as 1.5, but
this is the optimum pH for the protein-digesting enzyme pepsin that works in the stomach.
When eggs are heated, proteins that were dissolved in both the white and
the yolk are denatured. They become insoluble so both yolk and white
solidify
TURN OVER
FOR QUESTIONS
CLASS COPY DO NOT WRITE CLASS COPY DO NOT WRITE CLASS COPY DO NOT WRITE
The three-dimensional conformation of proteins is stabilized by bonds or interactions between R groups of
amino acids within the molecule. Most of these bonds and interactions are relatively weak and they can be
disrupted or broken. This results in a change to the conformation of the protein, which is called denaturation.
A denatured protein does not normally return to its former structure – the denaturation is permanent. Soluble
proteins often become insoluble and form a precipitate. This is due to the hydrophobic R groups in the centre of
the molecule becoming exposed to the water around by the change in conformation.
Heat can cause denaturation because it causes vibrations within the molecule that can break intermolecular
bonds or interactions. Proteins vary in their heat tolerance. Some microorganisms that live in volcanic springs or
in hot water near geothermal vents have proteins that are not denatured by temperatures of 80 °C or higher. The
best known example is DNA polymerase from Thermus aquaticus, a prokaryote that was discovered in hot
springs in Yellowstone National Park. It works best at 80 °C and because of this it is widely used in
biotechnology. Nevertheless, heat causes denaturation of most proteins at much lower temperatures.
Extremes of pH, both acidic and alkaline, can cause denaturation. This is because charges on R groups are
changed, breaking ionic bonds within the protein or causing new ionic bonds to form. As with heat, the threedimensional structure of the protein is altered and proteins that have been dissolved in water often become
insoluble. There are exceptions: the contents of the stomach are
normally acidic, with a pH as low as 1.5, but this is the optimum
pH for the protein-digesting enzyme pepsin that works in the
stomach.
When eggs are heated, proteins that were dissolved in both the
white and the yolk are denatured. They become insoluble so both
yolk and white solidify
TURN OVER
FOR QUESTIONS
In groups you will answer the following questions in your notebooks in complete sentences.
1.
2.
3.
4.
What does it mean for a protein to denature?
List two environmental conditions that can cause a protein to denature.
Once a protein is denatured, can it go back to its initial conformation?
Why do you think protein conformation can change based on the environment? Explain your answer
using your knowledge from class and this reading.
In groups you will answer the following questions in your notebooks in complete sentences.
1.
2.
3.
4.
What does it mean for a protein to denature?
List two environmental conditions that can cause a protein to denature.
Once a protein is denatured, can it go back to its initial conformation?
Why do you think protein conformation can change based on the environment? Explain your answer
using your knowledge from class and this reading.