Coded amino acids containing only two nucleotides

1. Would two nucleotides at a time be sufficient to provide enough codons to code for all 20 amino acids? Why or why not? How many amino acids could be coded for by codons containing only two nucleotides?

2. Will three nucleotides per codon work? Why or why not? Explain your answer.

3. What does poly U code for?

4. What amino acids (not nucleotides) do these polynucleotides code for?

poly A:

poly G:

poly C:

5. Refer to a codon chart. (NOTE: A Genetic Coding Dictionary can be found on the Internet or page 239 of your textbook-8th edition. It shows the amino acids manufactured according to the messenger RNA nucleotides in each codon.) Are the amino acids coded for by the polynucleotides you created consistent with what you would expect based on the codon chart?

6. If the code is read two bases at a time, what result would you expect for a polydinucleotide such as AUAUAUAU? Try it and see whether your prediction was correct.

poly AU:

7. Will you get a different result with UAUAUAUA than you did with AUAUAUAU? NOTE: In these crude extracts translation starts at a random location in the RNA sequence.

poly UA:

8. Translate all possible dinucleotides that use two different bases with TranslationLab. NOTE: List the two amino acids produced by the following combinations (the order of the two amino acids is random).

poly AG or GA:

poly AC or CA:

poly UG or GU:

poly UC or CU:

poly GC or CG:

9. Did you get all of the amino acids? If not, which ones are missing?

10. Did you get any amino acids more than once? Which one(s)?

11. What does this tell you about the code? (Is the real genetic code read two bases at a time?)

12. Translate the following trinucleotides. NOTE: List the three amino acids produced by the following combinations.

poly AAC or ACA or CAA:

13. Did you get the result you expected? Explain what happened. NOTE: Refer to a codon chart and list which amino acid will result from each of the following triplets, produced by three different starting points on the polytrinucleotide.




14. From these results can you now tell how many bases there are in a codon? If so, how many are there and how do you know this?

(NOTE: Omit the instructions for producing a tetranucleotide.)

15. Now try GGG, GGA, GGC, and GGU. NOTE: list the amino acids that result from each of the following triplets, with random starting points (remember to include results starting with the first base, the second base, and the third base).

poly GGG:

poly GGA:

poly GGC:

poly GGU:

16. What amino acid showed up in all four experiments?

17. Are there any codons shared in common by these four reactions? If not, then what must be true to explain your results?

18. What do the four polytrinucleotides in question 15 have in common?

19. Can you now say whether some positions in the codon are less important than others in specifying which amino acid is coded for?

Assignment 2:

20. What amino acid does the codon GAA specify?

21. Which amino acid is incorporated into the sickle-cell hemoglobin molecule when this codon is mutated to GUA?


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