Nucleic acids such as DNA and RNA are made up of monomers known as nucleotides. 

In the space below, draw the structure of a single DNA nucleotide. Include labels to show the names of each component.

Describe two differences between the structure of a DNA nucleotide and the structure of an RNA nucleotide.

Both DNA and RNA are synthesised by the formation of phosphodiester bonds between adjacent nucleotides. 

Describe how a phosphodiester bond is formed between nucleotides.

A researcher investigated the process of DNA replication in his laboratory.

He added an enzyme, multiple single-stranded DNA fragments, and a solution containing DNA nucleotides to a test tube. 

Name the enzyme he added to the reaction mixture. 

Suggest why he added DNA nucleotides to the reaction mixture.

Suggest why he added single-stranded DNA fragments. 

Explain why DNA replication is described as semi-conservative.

Scientists extracted DNA from a eukaryotic cell and examined the DNA strands in the laboratory.

They identified that 18% of the nucleotides within the DNA contained the nitrogenous base thymine.

Calculate the percentage of nucleotides within the DNA containing cytosine.

DNA molecules consist of two polynucleotide chains.

Describe how these two chains are held together.

DNA is replicated during the cell cycle in a process known as semi-conservative replication. 

Explain the role of enzymes involved in this replication process. 

DNA is a double-stranded polymer consisting of many nucleotides. 

Name the two scientists who proposed the current models of DNA structure and DNA replication.

Name the types of chemical bond: 

i) between complementary base pairs in DNA

ii) between adjacent nucleotides in a DNA strand

Describe how two DNA strands are separated during the process of DNA replication.

Describe two similarities and two differences between the structure of a DNA nucleotide and the structure of a molecule of ATP.

The diagram below shows a section of a molecule of DNA.

Name the parts labelled A, B, and C in the diagram above.

On the diagram below, draw a box around a single nucleotide. 

A DNA molecule contains 750 nucleotides. 28% of these nucleotides contain the base cytosine. 

Calculate the number of each nitrogenous base present in this molecule of DNA.

Explain how the structure of DNA is related to its function.

The diagram below shows a segment of DNA. 

Name the bond labelled A in the diagram above.

One of the bases is labelled as B in the diagram above. 

Suggest which base this could be.

DNA is a type of polymer.

Describe how the diagram provides evidence that DNA is a polymer. 

Each nucleotide within DNA contains a nitrogenous base. 

Explain how the nitrogenous bases provide stability to a molecule of DNA.

DNA molecules need to be replicated during the cell cycle. 

Describe how DNA is replicated inside the nucleus.

The diagram below shows a pair of complementary DNA nucleotides. One of the nucleotides contains thymine.

Name the nitrogenous base that pairs with thymine.

On the diagram below, draw hydrogen bonds to connect the two nucleotides.

Hydrogen bonds are broken in the process of DNA replication. 

Name the enzyme used to break hydrogen bonds between DNA strands. 

The structure of DNA enables its replication.

Describe two features of DNA that enable the process of semi-conservative replication.

Describe the structure of DNA.

RNA is an example of a nucleic acid used by organisms to synthesise proteins.

The diagram below shows the structure of an RNA nucleotide.

On the diagram below, draw a circle around the part that can form hydrogen bonds with another nucleotide.

RNA nucleotides can be joined together to form polynucleotides.

However, they are usually broken down shortly after serving their role in the body.

Describe how an RNA polynucleotide is broken down into single nucleotides.

DNA is another type of nucleic acid. 

Describe two similarities and two differences between the structure of DNA and the structure of RNA.

Scientists investigated the cell cycle and measured the percentage of cells undergoing DNA replication.

The scientists determined the percentage of cells undergoing DNA replication by using a chemical called 5-EdU.

Cells use 5-EdU instead of nucleotides containing thymine.

Describe how 5-EdU would be incorporated into a new DNA strand using the process of semi-conservative replication.

Meselson and Stahl carried out an investigation into the process of semi-conservative replication in DNA.

• They grew bacteria in a medium containing heavy nitrogen (N¹⁵).
• They then extracted the DNA from these bacteria and measured the density.
• The density is shown by the position of the band in the diagram below.
• The bacteria were then transferred to a different medium containing light nitrogen (N¹⁴).
• The bacteria were allowed to replicate once, before being transferred to another N¹⁴ medium.

Complete the diagram below to show the positions of the DNA bands in tubes 2 and 3.

Which part of a DNA nucleotide contains nitrogen?

Explain why the DNA in tube 2 is found in the position shown. 

Two nucleotides can join together via a phosphodiester bond to form a dinucleotide.

Name the chemical released when a phosphodiester bond is formed between two nucleotides.

Nitrogenous bases are grouped into two categories, known as purines and pyrimidines. 

Name two purine bases.

Explain how pairing of nitrogenous bases allows identical copies of DNA to be made.