Return to Blog Homepage

MCAT Biology Question — Nucleotide Structures

  • by John
  • Feb 13, 2017
  • MCAT Question of the Day

DNA and RNA are composed of long chains of monomers known as nucleotides. On the guanosine monophosphate molecule shown below, which arrow best indicates the 5’ end of the subunit?

guanine molecule

 

  1. I
  2. II
  3. III
  4. IV
Click for Explanation
This question is testing your familiarity of nucleotide structures found in DNA and RNA. Nucleotides are monomers, or subunits, that are the building blocks of DNA and RNA molecules. Each nucleotide consists of a phosphate group, a pentose ring, and a nitrogenous base. In the case of the guanosine monophosphate nucleotide shown, the 5’ end corresponds to the phosphate group attached to the fifth carbon on the pentose ring, indicated by the arrow labeled IV. This phosphodiester bond represents the 5’ of a nucleotide making choice D the best answer. The arrow labeled III corresponds to the third carbon in the pentose ring. The hydroxyl group attached to the third carbon represents the 3’ end of a nucleotide. The arrow labeled II represents the first labeled carbon. Lastly, arrow I points to the nitrogenous base of guanine.

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

Submit a Comment