At a physiological pH of 7.4, amino acids exist as zwitterions because the pKa o
ID: 1066716 • Letter: A
Question
At a physiological pH of 7.4, amino acids exist as zwitterions because the pKa of the -NH_3^+ group is 7, 4 and the pKa of the -COOH group is 7, 4 greater than/less than less than/less than less than/greater than equal to/equal to greater than/greater than Consider the following forms of the amino acid alanine (AIa). Which statement concerning these structures is FALSE? Structure III represents the form of Ala present in the acidic environment of the stomach. Structure IV represents the zwitterion of Ala. Structure II represents the form of Ala present in the basic environment of the intestines. Structure I represents the form of Ala present in the blood at physiologic pH. How is the following amino acid categorized? The structure shows its form at pH = 7. hydrophobic polar uncharged acidic basic Amino acids are the building blocks of proteins. Which of the following statements concerning amino acids is FALSE? There are 20 different amino acids that occur naturally in human proteins. The amino acids present in human proteins are "alpha" amino acids. The amino acids that make up human proteins are called essential amino acids. Except for glycine, where R = H, amino acids are chiral molecules. Amino acids are classified by the nature of the side chain R groups that are present.Explanation / Answer
4.
At a physiological pH of 7.4, amino acids exist as zwitterions because the pKa of –NH3+ group is greater than 7.4 and the pka of –COOH group is less than 7.4.
As –NH3 represents basic terminal of amino acid its pKa is higher and –COOH is acidic terminal therefore less pKa.
5.
Statement d is FALSE.
Zwitterion form of alanine has –COO-(at pH=6) and pH of blood is around 7.4. Therefore, -COOH is impossible at pH 7.4 and as pH increases H from –COOH leaves to form –COO-.
6.
We can categorize this amino acid as hydrophobic as its side chain is hydrophobic. Even though its side chain is polar it has neutral charge at physiological pH.
7.
Statement c is FALSE.
Amino acids that cannot be synthesized by humans are called as essential amino acids.
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