Serine exists in its zwitterion form at a pH of 5.7. Draw the structural formula for the same. Explain the manner in which the structural formula of polar and non-polar amino acids would vary
You have to look at the Pka's of the carboxylic acid and the amine to know if they will be charged at a pH of 5.7; the amine will be positively charged and the carboxylic acid will be negatively charged at a pH of 5.7.
I can not draw structures on this forum, but I am pretty sure that you can google an image of the structure with the indicated charges.
To draw the structural formula of serine in its zwitterion form at a pH of 5.7, we first need to understand the concept of zwitterions. A zwitterion is a molecule that carries both a positive and negative charge, essentially making it electrically neutral overall.
Serine is an amino acid, and its general structure consists of an amino group (-NH2), a carboxyl group (-COOH), and an R group. The R group in serine consists of a hydroxymethyl (-CH2OH) group.
To draw the structural formula of serine in its zwitterion form at pH 5.7, we need to consider the pKa values of the functional groups present in serine. The pKa is the pH at which half of the molecules of a specific compound exist in their protonated form and the other half exist in their deprotonated form.
The pKa of the carboxyl group (-COOH) in serine is around 2.2, which means that at a pH greater than 2.2, the carboxyl group tends to lose a proton and exists in its deprotonated form (-COO-). The pKa of the amino group (-NH2) in serine is around 9.2, which means that at a pH lower than 9.2, the amino group tends to accept a proton and exists in its protonated form (-NH3+).
At pH 5.7, which is between the pKa values of the carboxyl and amino groups, serine exists in its zwitterion form. In this form, the carboxyl group is deprotonated (-COO-) while the amino group is protonated (-NH3+).
Here is the structural formula of serine in its zwitterion form at pH 5.7:
O
//
H3N+ -- C -- C
\
OH
Now, let's explain how the structural formula of polar and non-polar amino acids would vary.
Polar and non-polar amino acids differ based on the nature of their R groups. In general, polar amino acids have R groups that can form hydrogen bonds with water or other polar molecules, whereas non-polar amino acids have R groups that cannot form hydrogen bonds and are hydrophobic in nature.
The R group of polar amino acids often contains functional groups such as hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), or sulfur (-SH). These functional groups increase the polarity of the molecule, and the presence of polar bonds makes the overall amino acid molecule more hydrophilic (water-loving).
On the other hand, non-polar amino acids have R groups that are mostly composed of hydrocarbon chains or aromatic rings. These hydrophobic R groups do not readily interact with water or polar molecules, making the overall amino acid molecule more hydrophobic (water-fearing).
Therefore, the main difference between the structural formula of polar and non-polar amino acids lies in the nature of their R groups. Polar amino acids have R groups containing functional groups that increase the polarity of the molecule, while non-polar amino acids have R groups that are hydrophobic in nature.