Complete question:
A gene has a base sequence of GTC. Due to a mutation, the base sequence changes to GTG. Answer the following questions:
a) What are the bases of mRNA coded for by this section of DNA, before the mutation? (1 point)
b) What are the bases of mRNA coded for by this section of DNA, after the mutation? (1 point)
c) What amino acid is coded for by this sequence before the mutation? (1 point)
d) What amino acid is coded for by this sequence after the mutation? (1 point)
e) Is this is a silent mutation or a missense mutation? Explain. (1 point)
Answer:
a) mRNA before mutation ⇒ CAG
b) mRNA after mutation ⇒ CAC
c) amino acid before mutation ⇒ Glu, Glutamine
d) amino acid after mutation ⇒ His, Histidine
e) missense mutation
Step-by-step explanation:
Theoretical frame
Transcription occurs in the nucleus where the template DNI strand is read in direction 3´→ 5´ to build the mRNA molecule in direction 5´→ 3´.
When the DNI molecule separates into two strands to form the transcription bubble, we can identify two separate segments: coding strand and template strand.
The coding strand goes in direction 5´ to 3´, while the complementary strand -template strand- grows in direction 3´ to 5´.
The template strand is the mRNA complement.
The coding strand is the same as the mRNA that results from the transcription of the same DNI segment -switching bases T for U-.
The coding strand receives that name because it is the sequence that codes for each amino acid composing the proteins.
Translation occurs in the cytoplasm. rRNA and tRNA read mRNA in the direction 5´→ 3´ to build the protein.
Genetic information for the aminoacids assembly during the protein synthesis is stored in short sequences of three nucleotides named codons in the mRNA. Each of the codons represents one of the 20 amino acids used to build the protein. There are 64 codons in total, from which 61 codify for amino acids. Because there are 20 amino acids, many codons code for the same amino acid. One of these amino acids is also the start point of protein synthesis. And the left three codons are stopping translation points.
The codons indicating the initiation or stop points during the translation process are:
• The start codon AUG is the most common sequence used by eukaryotic cells
• The end codons are UAA, UAG, UGA.
When a change occurs in a single base pair, it is known as a point mutation. Points mutations might be either silent, missense, or nonsense. In silent mutations, the resulting mRNA codon codes for the same amino acid as the unmutated sequence. However, if the mutation causes the mRNA codon to code for a different amino acid, this mutation is a missense mutation. Finally, if the mutation causes mRNA codon to be a stop codon, we are referring to a nonsense mutation.
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In the exposed example,
Before mutation
- Original DNI base sequence ⇒ GTC ⇒ Guanine, Timine, Cytokine
- Transcripted mRNA sequence ⇒ CAG ⇒ Cytokine, Adenine, Guanine
- Amino acid ⇒ Gln ⇒ Glutamine
After mutation
- Mutated DNI base sequence ⇒ GTG ⇒ Guanine, Timine, Guanine
- Transcripted mRNA sequence ⇒ CAC ⇒ Cytokine, Adenine, Cytokine
- Amino acid ⇒ His ⇒ Histidine
This is a point mutation, in which the change occurs in a single base pair. The mutation made the mRNA codon code for a different amino acid, meaning that this is a missense mutation.
- Before mutation, the mRNA codon is CAG and codes for Glutamine.
- After mutation, the mRNA codon is CAC and codes for Histidine.