1.1. Ricin is a protein produced by castor beans. In animal cells, ricin acts as an enzyme. This enzyme removes the adenine molecule from one of the nucleotides in the RNA of ribosomes. As a result, the ribosome changes shape.

Ricin causes the death of cells and is very poisonous to many animals.

Suggest how the action of ricin on ribosomes could cause the death of cells.   

1.2. Draw labelled diagrams comparing an mRNA and a tRNA molecule.

1.3. Table 1 below shows some mRNA codons and the amino acids for which they code.

Table 1

i) Give the DNA sense strand sequence for leucine.

ii) Name the amino acid carried by the tRNA with the anticodon CAU.

1.4. Cycloheximide binds to specific sites on the eukaryotic ribosomes. This is shown in Figure 1 below.

Figure 1

Explain how cycloheximide stops protein synthesis.