Biochemistry - Structure and Properties of Amino Acids - Discussion

Discussion Forum : Structure and Properties of Amino Acids - Section 1 (Q.No. 11)
Which of the following pairs of amino acids would carry a negative charge on their side chain at pH 8.0?
Asparagine & Glutamine
Leucine & Glycine
Histidine & Lysine
Aspartate & Glutamate
Answer: Option
No answer description is available. Let's discuss.
9 comments Page 1 of 1.

Nyalema said:   2 years ago
Well explained, Thanks all.

Syrous Arinaitwe said:   3 years ago
You did it, well explained.

Syrous Arinaitwe said:   3 years ago
You did it, well explained.

Abel said:   4 years ago
The question is every amino acid when placed in basic solution.

It will Cary a net negative charge.(Lippincott biochemistry) Nh3+----c-----coo- in basic solution Nh3+ will loss a proton and coo- remains.

Nikhil said:   6 years ago
At alkaline, pH amino acids are in the form of cations so, at pH 8. 0 the amino loses its hydrogen group and forms an - ve charge.

Nikki said:   8 years ago
Consider these groups COOH, NH3, COOH.

At pH 8.0, the first COOH group loses its H+ because its pKa is BELOW 8.0.

At pH 8.0, the NH3 still has its proton because its pKa is ABOVE 8.0.

So we are so far left with a 0 charge.

But in Aspartate and Glutamate, we have an EXTRA COOH (R group), which has lost its proton at pH 8.0 because its pKa is BELOW 8.0.

So overall we have a -1 charge.

Alby said:   8 years ago
pKr of Glutamate is 4.25.

pKr of Aspartate is 3.65.

If pH, for example the pH of 8, is greater than the pKr, then the amino acid loses a proton and bears its negative charge.

If the pH is less than the pKr value, then the amino acids keeps its proton, bearing a neutral charge.

PH of 8 is greater than the pKr values of Glu and Asp, so they both lose a proton and bear that negative charge on their respective are group.

Subarna said:   9 years ago
Why aspartate and glutamate carry -ve charge at ph 8?

Jyoti shah said:   9 years ago
Do not get the reason behind it?

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