IMAT 2018 Q36 [Peptide Bonds]

Which of the following contain peptide bonds?

  1. ribosomes in human liver cells
  2. antibodies in human plasma
  3. cilia on human bronchial cells
  4. cholesterol in the membrane of human kidney cells

A. 2, 3 and 4 only
B. 1 and 3 only
C. 1 and 4 only
D. 2 and 4 only
E. 1, 2 and 3 only

The answer to this question is choice E.

The key to answering this question is to establish the significance of peptide bonds: Basically peptide bonds function to bind amino acids together, and as you know, amino acids are the most basic unit of proteins! Thus, simply put, you will just need to analyze which of the statements contain proteins in order to be included in your considerations.

Let us look at each of the statements:

  1. “Ribosomes in human liver cells”: The structure pertained to here are the ribosomes, which is the cellular machinery used to create proteins. Keep in mind, that ribosomes themselves are made up of RNA and protein, thus, it would make sense that ribosomes do indeed contain peptide bonds.
  2. “Antibodies in human plasma”: Antibodies are immunoglobulins that are produced by the immune system in response to foreign agents or microbes. Antibodies are proteins that are produced by B lymphocytes, which makes this a correct consideration.
  3. “cilia on human bronchial cells”: As you can recall, cilia, or the hair-like structures, are made of microtubules. Microtubules in turn, are made of units called tubulin, which are proteins. Thus, cilia ultimately also contains peptide bonds, given its protein nature.
  4. “cholesterol in the membrane of human kidney cells”: cholesterol is NOT a protein, which eliminates this from your considerations. Cholesterol rather, is a sterol compound that is made of a sterol nucleus that consists of 4 hydrocarbon rings and a hydroxyl group. This then makes choice E as the only correct answer.

Reminder: Do not be misled or confused about the location of the structures that the question gives you, like “in human liver cells” in statement 1, and “on human bronchial cells” in statement 3. Rather, just focus on the structure itself, and analyze from there, since the location is irrelevant in terms of discerning whether or not that structure is a protein.