Question

Translation: From RNA to Protein

1. How is it possible that 4 nucleotides can code for 20 amino acids?

2. What is meant by the fact that the genetic code is redundant?

3. How is tRNA involved in the process of transcription?

4. How is it possible that 31 different tRNAs can translate 64 different codons?

5. Describe the process by which tRNA and amino acids are joined.

6. What is the role of ribosomes in translation? Describe how the structure of ribosomes fit their function.

7. What is the codon that is responsible for initiating translation? How does the presence of this codon aid in the initiation of the translation process?

8. Describe the process of initiating translation.

9. Describe the process of elongation during translation. How do codons move through the ribosome? In which site of the ribosome are new amino acids added to the growing polypeptide chain?

10. What are the three stop codons used in translation? How do they stop the process of translation?

11. Why does translation occur in a 5’ to 3’ direction when DNA is read in a 3’ to 5’ direction?

12. Define polyribosomes.

13. What is the role of polyribosomes in the cell? Why is it important for the cell to have the ability to create polyribosomes?

14. Many pharmaceuticals target ribosomes and interfere with translation. How do these pharmaceuticals affect cellular function?

15. A new pharmaceutical targets the A site of the ribosome. Describe, in detail, at what stage of the process of translation this pharmaceutical would affect the ribosome.

Answer 1

1) Each amino acid is coded by a codon consists of three nucleotides. Mathematically 4 nucleotides can make up 4³ or 64 different combinations (codons) taking three nucleotides at a time. Thus, 64 codons (3 are stop codons) are available for only 20 amino acids. In this way 4 nucleotides are able to code 20 amino acids.

2) The fact that genetic code is redundant implies that a single amino acid can be coded by more than one codon (20 amino acids are coded by 61 codons; 3 are stop codons). Thus it is called that genetic code is degenerate or redundant.