Nitrogen Bases, Nucleosides and Nucleotides
Every living cell stores its instructions in nucleic acids, and those nucleic acids are built from remarkably small nitrogen-containing units. This quiz tests Lesson 4 of the Biomolecules course, where you meet the five heterocyclic nitrogen bases — adenine, guanine, cytosine, uracil and thymine — and follow them up the ladder of organisation:
- Nitrogen base — a heterocyclic ring carrying nitrogen.
- Nucleoside — a base attached to a sugar (adenosine, guanosine, thymidine, uridine, cytidine).
- Nucleotide — a nucleoside with a phosphate group esterified to the sugar (adenylic, guanylic, thymidylic, uridylic and cytidylic acid).
The whole distinction between a nucleoside and a nucleotide is a single phosphate group — yet that group is exactly what lets nucleotides link into the long chains of DNA and RNA, the polymers that function as genetic material. Work through the fifteen questions below to check that you can name the bases, classify them, and move confidently between the three levels of structure.
Q1. Which set correctly lists the five nitrogen bases named in the lesson?
The lesson names exactly five nitrogen bases: adenine, guanine, cytosine, uracil and thymine. Ribose, phosphate and glycerol are not nitrogen bases.
Q2. In the lesson, a nitrogen base found attached to a sugar is called a:
The lesson states that when the nitrogen bases are found attached to a sugar they are called nucleosides. A nucleotide requires an additional phosphate group.
Q3. According to the lesson, what must be esterified to the sugar to convert a nucleoside into a nucleotide?
The lesson says that if a phosphate group is also found esterified to the sugar, the unit is called a nucleotide. The phosphate is the single distinguishing feature.
Q4. Which of the following is a nucleoside named in the lesson?
Adenosine is listed among the nucleosides (with guanosine, thymidine, uridine and cytidine). Adenylic, guanylic and cytidylic acids are nucleotides.
Q5. Which of the following is a nucleotide named in the lesson?
Thymidylic acid is listed among the nucleotides. Thymidine, uridine and cytidine are nucleosides, lacking the phosphate group.
Q6. The lesson states that nucleic acids such as DNA and RNA consist of:
The lesson explicitly states that nucleic acids like DNA and RNA consist of nucleotides only — the phosphorylated monomers, not bare bases or nucleosides.
Q7. According to the lesson, what function do DNA and RNA perform?
The lesson closes by stating that DNA and RNA function as genetic material. Their catalytic and membrane roles are not part of this lesson.
Q8. A heterocyclic ring, as described in the lesson, is best understood as:
A heterocyclic ring contains at least one atom that is not carbon. In the nitrogen bases, the additional ring atoms are nitrogen.
Q9. Which pair of nucleosides is correctly matched with its corresponding nucleotide?
Adenosine is the nucleoside and adenylic acid its nucleotide. The other pairs mix bases: guanylic acid pairs with guanosine, thymidylic acid with thymidine, and adenylic acid with adenosine.
Q10. Which of the following lists contains ONLY nucleotides?
Adenylic, guanylic and cytidylic acids are all nucleotides. The second and third options are nucleosides, and the fourth lists bare nitrogen bases.
Q11. Which of the following lists contains ONLY nucleosides?
Guanosine, thymidine and uridine are all nucleosides. The other options each include a nucleotide (guanylic acid, thymidylic acid or uridylic acid).
Q12. The nucleotide formed from the base thymine is named:
The lesson lists thymidylic acid as the nucleotide corresponding to thymine. Thymidine is the nucleoside, which lacks the phosphate group.
Q13. Which statement best captures the three levels of organisation described in the lesson?
The lesson builds cumulatively: a bare nitrogen base, a nucleoside once attached to a sugar, and a nucleotide once a phosphate group is esterified to that sugar.
Q14. Which of the following is NOT a nitrogen base named in the lesson?
Ribose is a sugar, not a nitrogen base. The lesson names adenine, guanine, cytosine, uracil and thymine as the nitrogen bases.
Q15. A student says a sample contains cytidylic acid. Based on the lesson, this sample contains:
Cytidylic acid is listed among the nucleotides, so it is a nucleotide. Its nucleoside counterpart is cytidine, and its base is cytosine.