Amino Acids

Amino acids are the chemical building blocks of proteins, or polypeptides, and comprise a set of 20 different molecules. Fully assembled proteins consist of a long chain of amino acids held together by linkages known as peptide bonds. The general structure of an amino acid is characterized by three chemical groups: an amino group, a carboxylic acid group, and a side group that varies depending upon the type of amino acid. At the pH found within most living cells, or physiological pH, the amino group of the molecule has a plus (+) charge and the carboxylic acid group has a minus (-) charge. The charge of the side group varies with the type of amino acid. Amino acids may also adopt alternate tautomeric forms, or structures, as shown here. This does not change the chemical composition of the molecule, but simply rearranges its hydrogen atoms. The alternate structure adopted by this amino acid allows it to form linkages called peptide bonds with other amino acids. When a peptide bond is formed, two adjacent amino acids together lose two hydrogen atoms and one oxygen atom, resulting in production of a water molecule by a process called condensation. As this occurs, the carbon atom linked to the remaining oxygen of one amino acid forms a bond with the nitrogen atom of the other amino acid. When this process is repeated for a large number of amino acids, a long chain of molecules known as a polypeptide or protein is formed.

Question 1: Fully assembled proteins consist of a long chain of amino acids held together by _____________ bonds.
  1. ionic
  2. peptide
  3. hydrogen
  4. covalent


Answer 1 Answer - (b) peptide

Question 2: What are the three chemical groups that make up the structure of an amino acid?
  1. An amino group, a sugar, and a protein.
  2. A peptide, a carboxylic acid, and a side group.
  3. An amino group, a carboxylic acid group, and a side group that varies depending upon the type of amino acid.
  4. An amino group, a carboxic acid group, and a side group that varies depending upon the type of amino acid.


Answer 2 Answer - (c) An amino group, a carboxylic acid group, and a side group that varies depending upon the type of amino acid

Question 3: How many hydrogen and oxygen atoms are lost when a peptide bond is formed between two adjacent amino acids?
  1. Two hydrogen atoms and one oxygen atom.
  2. One hydrogen atom and one oxygen atom.
  3. Two oxygen atoms and one hydrogen atom.
  4. The numbers vary depending on the amino acids involved.


Answer 3 Answer - (a) Two hydrogen atoms and one oxygen atom

Question 4: What does it mean to tautomerize?
  1. To have a stable shape that never changes
  2. To have additional peptide groups
  3. To change shape but have the same chemical composition
  4. To fold DNA molecules tightly


Answer 4 Answer - (c) To change shape but have the same chemical composition