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THE GENETIC CODE
The Genetic Code – Francis Crick (1962)
1. What was the coding problem?
2. How does Crick distinguish between the more general and specific aspects of
the coding problem?
3. What organism was used by Crick and colleagues to study the general aspect
of the coding problem? Describe the RII locus of this organisms genome.
4. How did creating “recombinant bacteria” help them study specific mutations?
5. Why was it mathematically logical that the genetic code for a single amino acid
consisted of three DNA nucleotide bases?
6. How were George Gamow’s (founder of the RNA Tie Club) thoughts about the
code proved experimentally wrong?
7. What did Crick and colleagues find to be interesting when multiple mutants in
a single gene were studied? What predictive rules did they uncover?
8. What is a “nonsense triplet”? How did it help explain why more distantly
spaced plus and minus mutants are more likely to be non-functional? How
did they restore such genes activity?
9. How do mutations suggest that genes are true and separate entities?
10. What happened when Crick and colleagues created T4 recombinants with
three plus mutants fairly close together? How does viewing the code as a
triplet code explain these results?
11. How is the code “degenerate”
The Genetic Code II – Nirenberg (1963)
1. How many genes were suspected to occur in the human genome at this time?
2. Who coined the term “messanger RNA”, and how are amino acids prepared
and transfer to the site of the mRNA?
3. Describe a cell-free system?
4. How were synthetic monotonous mRNA molecules used to provide evidence
for the first two codons?
5. How were synthetic mRNA molecules with two kinds of bases used in trying to
determine possible codons?
6. How can the code be said to be “universal”?
7. What experiment was conducted to determine whether it was the amino acid
or the tRNA that recognized the codon?
The Genetic Code III – Francis Crick (1966)
1. How was synthetic mRNA limited in determining the code?
2. Describe and create a diagram expressing the details of the new technique by
Nirenberg and Leder used to determine codons.
3. How did Khorana and colleagues use more specifically produced mRNA
molecules to determine the codons? and how did their work provide
convincing evidence for a triplet code?
4. How did correlating specific mutant genes and their protein products support
knowledge of the code?
5. What does the “wobble” in the wobble hypothesis refer to?