Question

1. Describe what the “genetic code” means. What is a codon? Anticodon? Stop codon?

2. How to you take a DNA sequence and deduce a codon/anticodon, template, nontemplate strand?

3. Describe the characteristics of a tRNA. Why are these molecules considered bifunctional?

4. What is the wobble hypothesis? (codon-anticodon interactions)

5. How are amino acids activated?

Answer 1

1. Genetic code refers to triple codons present in mRNA that specify amino acids in the protein. Each amino acid is encoded by one or more codons. There are 61 codons that specify 20 natural amino acids found in cells. Anticodon is the complementary sequence to triplet codon present in the tRNA. Stop codons are UAA, UAG, and UGG. These codons do not specify any amino acids. hence translation stops when these codons are encountered on the mRNA.

2. The genetic code is triplet and commaless. Translation starts at AUG codon. So, we need to check for AUG codon on the DNA sequence and deduce downstream coding sequence. Anticodon sequences are complementary to the coding sequence.

See image.

3. tRNA = Transfer RNA. It is also known as adapter RNA or soluble RNA. It shows cloverleaf structure and contains four arms. The anticodon arm is complementary to codon sequence. The amino acid arm is charged with the corresponding amino acid. They are bifunctional in the sense that they read the codons as well as bring corresponding amino acids into the ribosome.

4. Wobble base pairing refers to liberal base-pairing at the third base position of the codon-anticodn pair.

5. Amino acids are activated by tRNA synthetases which attach them to tRNAs to form aminoacyl tRNAs that participate in the translation process.