Question

For each different mutant cell described below, assume that ONE nucleotide has been mutated in the sequence so that the protein's function has changed. Name as many single nucleotide changes that could result in the description. 

Cell 3: mRNAs are able to bind to small ribosomal subunits, but nothing happens after they bind. Large ribosomal subunits are floating in the cytoplasm, and no proteins are made. 

Nonsense mutation that adds a new stop codon before the original stop codon. 

Deletion mutation that deletes three codons creating a new stopping point on the DNA 

Duplication mutation that doubles the length of the amino acid sequence. 

Missense Mutation causes the start codon to not exist so translation cannot continue

Answer 1

• Translation starts from start codon (AUG) and ends at stop codon (UAA, UAG,UGA).
• For translation initiation, it is essential for the ribosome to bind with the mRNA.
• Ribosomal subunits need to be separated for mRNA to be inserted to interact with the corresponding tRNA.

• In eukaryotes, the AUG codon is the start codon for the process of translation. In prokaryotic cells, GUG and UUG codons also function as start codons. Messenger RNA or m RNA carries the genetic code received from the DNA, in 5’to 3 ‘direction reading frame. The initiator t-RNA (with anticodon (UAC) recognizes the start codon, which is essential for initiation of translation.

• During translation, tRNA carries amino acid to the ribosome, by matching anticodons to codons in mRNA.
• The secondary structure of tRNA form the clover leaf structure with the anticodon arm having complementary nucleotides for base pairing with codons in mRNA.
• The first aminoacyl tRNA is located in the P-site and second in the A site.

• If there is a mutation that inserts a stop codon before start codon, translation will not be initiated.

• Similarly if mutation results in change of start codon to any other codon, the tRNA will not bind to initiate translation.

Answer: options 1 and 4.