If the side chain of a glutamic acid residue has a pKa of 4.1, at pH 6.1 the ratio of uncharged to charged side chain would be about

A. 100:1
B. 10:1
C. 1:1
D. 1:10
E. 1:100
-i HAVE NO IDEA

Which of the following amino acids has a side chain that can serve ONLY as a hydrogen bond donor but NOT as a hydrogen bond acceptor in its predominant form at pH 7?
A. N
B. V
C. E
D. K
E. H

-I think this one is D

PLEASE HELP SOMEONE!

To answer these questions, we need to understand the concepts of pKa and pH and their relationship to the ionization state of amino acid side chains.

1. For the first question, we are given that the pKa of the glutamic acid side chain is 4.1. The pKa is the pH at which half of the acid side chains are neutral (uncharged) and half are ionized (charged). In this case, the pKa is lower than the pH of 6.1, which means the side chain will be mostly ionized (charged) at pH 6.1. The higher the pH is above the pKa, the more ionized the side chain will be. So, the ratio of charged to uncharged side chains will be high. This indicates that the correct answer is option E, 1:100.

2. For the second question, we need to identify the amino acid with a side chain that can serve only as a hydrogen bond donor but not as a hydrogen bond acceptor at pH 7. Hydrogen bond donors are atoms that can donate hydrogen atoms, while hydrogen bond acceptors are atoms that can accept hydrogen bonds. At pH 7, we need to consider the predominant form of amino acids. Among the options, lysine (K) and histidine (H) are known to have both hydrogen bond donor and acceptor ability. Alanine (A) and valine (V) do not have any hydrogen bond donor or acceptor groups in their side chains. However, aspartic acid (D), also known as aspartate, has a side chain carboxyl group that can only serve as a hydrogen bond donor, not as a hydrogen bond acceptor. Therefore, the correct answer is option C, aspartic acid (D).

Remember, understanding the concepts of pKa, pH, and the properties of amino acid side chains will help you arrive at the correct answers.