1. Explain why DNA is described as a polymer.
Answer
It is made up of repeating units/monomers (called nucleotides).
2. Explain why DNA replication is described as being semi-conservative.
Answer
Both strands act as a template. The new DNA molecule is made up of one old and one new strand.
3. How does a DNA molecule form a double helix ?
Answer
Two polynucleotide strands are joined together by hydrogen bonds between complementary base pairs.
4. Describe the process of DNA replication.
Answer
DNA helicase unwinds the double helix and breaks the hydrogen bonds, effectively unzipping the strands. Each strand then acts as a template. Free DNA nucleotides are attracted to the exposed template strands through specific complementary base pairing. DNA polymerase joins adjacent nucleotides by catalyzing the formation of phosphodiester bonds in a condensation reaction.
5. Identify which component(s) of the DNA contains heavy nitrogen.
Answer
Bases A, C, T and G.
6. Gemcitabine is a drug that is used to treat cancer. The figure below shows gemcitabine as well as cytosine and thymine nucleotides. Gemcitabine is injected into the blood. An enzyme adds a phosphate group at the point shown. Explain how gemcitabine stops DNA replication.
Answer
Gemcitabine is similar in shape to a nucleotide. It is incorporated into DNA and pairs with guanine or adenine. However, it cannot form a phosphodiester bond because it lacks a phosphate group, so it cannot join to the next nucleotide.
7. Draw and label a nucleotide of RNA.
Answer
8. Scientists believe that the earliest living things had RNA as their genetic material. However, all living organisms today have DNA as their genetic material. Suggest the advantage of this.
Answer
DNA is double stranded, so it is more stable.