In each set of terms given below, there is an odd one and cannot be grouped in the same category to which the other three belong. Identify the odd term in each set and name the category to which the remaining three belong. Example: Ovary, Fallopian tube, Ureter, Uterus. Odd term: Ureter. Category: Parts of female reproductive system.
Thymine, Cytosine, Adenine, Pepsin.
Topic: Nitrogenous bases
Answer
Odd term: PEPSIN. Category of the others: NITROGENOUS BASES (of DNA).
Thymine, cytosine and adenine are three of the four NITROGENOUS BASES of DNA (the fourth being guanine).
PEPSIN is an ENZYME — a protein secreted by the gastric glands of the stomach to digest proteins. It has nothing to do with the genetic code.
THE POSSIBLE CONFUSION: the bases are called NITROGENOUS because they contain nitrogen, and pepsin, being a protein, also contains nitrogen. But the category is not "things containing nitrogen" — it is the specific set of bases that build DNA.
A useful clue in the names: most enzymes end in -ASE or, like pepsin and trypsin, in -IN following an older convention.