Proteins have a negative charge?

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drdrdrdrdrdrdr

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Hi everyone,

An EK instructor made a point of saying that proteins are negative
(I believe she was referring to cell receptors, and even possibly hormones, among others)

I have asked around to clarify this point, and have gotten the same answer that amino acids that make up proteins can be + or - charge and that proteins being - is nonsense

I'm still hung up on the point and was wondering if anyone would know what this is about?

Thanks in advance

btw, I am no longer in the class and have access to my EK instructors! Hence this post

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Amino acids are typically zwitterions, right? The carboxylic acid can deprotonate to make it negatively charged, or an amine can be protonated to make it positively. The state of protonation depends on the pH of the solution.

Carboxylic acids are obviously acidic (with amino acids, their pKa is 2-3), so at cellular pH, 7.4, they deprotonate and they are negatively charged. The amine has a pKa of about 10, if i remember correctly. So at 7.4, it is protonated.

Thus, at cellular pH, it exists as half negative charge, and half positive charge for a net neutral charge.

There are acidic and basic R groups that can change the net charge of the amino acid and can therefore grant it a net positive (basic) or negative (acidic) charge.
 
The charge a protein has at physiological pH is going to depend on the side chains. Chiddler is correct about all that, so I don't know what your EK instructor was talking about--sounds like you got out at the right time! She could have been thinking about DNA I guess...
 
Amino acids are typically zwitterions, right? The carboxylic acid can deprotonate to make it negatively charged, or an amine can be protonated to make it positively. The state of protonation depends on the pH of the solution.

Carboxylic acids are obviously acidic (with amino acids, their pKa is 2-3), so at cellular pH, 7.4, they deprotonate and they are negatively charged. The amine has a pKa of about 10, if i remember correctly. So at 7.4, it is protonated.

Thus, at cellular pH, it exists as half negative charge, and half positive charge for a net neutral charge.

There are acidic and basic R groups that can change the net charge of the amino acid and can therefore grant it a net positive (basic) or negative (acidic) charge.

The charge a protein has at physiological pH is going to depend on the side chains. Chiddler is correct about all that, so I don't know what your EK instructor was talking about--sounds like you got out at the right time! She could have been thinking about DNA I guess...

Yup. wikipremed explains this very well in one of the protein lectures.
 
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