THE MOLECULAR BASIS OF INHERITANCE
GENE MUTATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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mRNA has a STOP codon that gets read by the ribosome.
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tRNA has a STOP codon that gets read by the ribosome.
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The ribosome stops reading mRNA on its own, with no signal.
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The mRNA strand moves all the way through the ribosome, and once there is no mRNA left, the ribosome stops.
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Detailed explanation-1: -The end of the protein-coding message is signaled by the presence of one of three codons (UAA, UAG, or UGA) called stop codons (see Figure 6-50). These are not recognized by a tRNA and do not specify an amino acid, but instead signal to the ribosome to stop translation.
Detailed explanation-2: -Ribosomal profiling has shed new light on how ribosomes can ignore stop codons in messenger RNA. When a ribosome is translating a molecule of messenger RNA (mRNA) to produce a protein, it stops when it encounters a triplet of nucleotides called a termination codon.
Detailed explanation-3: -Lastly, termination occurs when the ribosome reaches a stop codon (UAA, UAG, and UGA). Since there are no tRNA molecules that can recognize these codons, the ribosome recognizes that translation is complete. The new protein is then released, and the translation complex comes apart.
Detailed explanation-4: -Ribosomes recognize three different termination codons – UAG, UAA and UGA – but a genetic event called a nonsense mutation can change a codon that normally codes for an amino acid – such as UAU, which codes for tyrosine – into a codon that stops translation prematurely.
Detailed explanation-5: -The presence of a stop codon-UAA, UAG or UGA-in the A site of the ribosome is generally a signal to terminate protein synthesis. This process constitutes the last essential stage of translation, as it ensures the formation of full-sized proteins.