Lesson 7 Biochem Part 6

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sarahgub
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Joined: Thu Dec 27, 2018 7:54 am

Lesson 7 Biochem Part 6

Post by sarahgub » Sat Apr 25, 2020 11:02 am

For question 12 on the timed practice passage, it asks to explain why disulfide links are rarely found intracellularly in the human body. The answer was A but I'm confused? Paragraph 1 said that acidic/oxidizing conditions will cause in vitro lysing. But then paragraph 2 says that they are insoluble unless exposed to dissociating/reducing agents. Can someone please explain this to me??
-Sarah :D
NS_Tutor_Mathias
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Re: Lesson 7 Biochem Part 6

Post by NS_Tutor_Mathias » Sun Apr 26, 2020 8:43 pm

Notice that the lysing described occurs in the presence of extremely strong acids, in strongly non-physiological conditions. In physiological oxidizing conditions, disulfide bridges are formed between cysteine residues. The processes shown in the diagrams (following the statement in paragraph 1) show for instance the oxidation to sulfite (oxidation state of sulfur: +5!) - but cells don't produce high concentrations of intracellular acetic acid.

So both things are actually true. Oxidizing environments are relatively less common intracellularly (not as uncommon as the question suggests, but we can gloss that over), and so disulfide bonds between cysteine residues to form cystine should also be less common. I'm glad you caught this, because it is a good point - even though the question and passage are both correct.

If you want to know a bit extra about common instances of disulfide bridge formation (cough, often intracellularly), read this:
https://en.wikipedia.org/wiki/Glutathione
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