Question

1. a frameshift mutation involves the addition or a deletion of a base in the nitrogen base sequence. given the following mrna codon sequence: aug uau gag aau uaa a) what would happen if the g at the end of the aug codon were deleted? b) what would happen if an additional base were inserted between the first and second codons?

Explanation:

Part (a)

Step 1: Analyze original codons

Original mRNA codons: AUG, UAU, GAG, AAU, UAA. Each codon is 3 bases. If G at end of AUG (AUG becomes AU) is deleted, the reading frame shifts.

Step 2: Determine new codon sequence

New sequence (after deleting G from AUG): AU (from AUG), U (from next codon's first base? Wait, no—original AUG is first codon (bases 1 - 3: A, U, G). Deleting G (base 3) makes the first "codon" AU (bases 1 - 2), then the next base is U (from UAU, base 1), so new codons: A UU (wait, no, let's list all bases. Original bases: A U G U A U G A G A A U U A A. After deleting G (position 3), the bases are A U U A U G A G A A U U A A. Now, reading frame is shifted. So first codon: AUU, then AUG, then AGA, then AUU, then AA... Wait, no, original codons are AUG (1 - 3), UAU (4 - 6), GAG (7 - 9), AAU (10 - 12), UAA (13 - 15). Deleting G (position 3) makes the sequence: A U U A U G A G A A U U A A. Now, reading from start (position 1): codon 1: A U U (1 - 3), codon 2: A U G (4 - 6), codon 3: A G A (7 - 9), codon 4: A A U (10 - 12), codon 5: U A A (13 - 15)? Wait, no, original UAU is bases 4 - 6 (U, A, U). After deleting G (position 3), base 4 is still U, but the first codon is now AU (positions 1 - 2) + U (position 4)? No, I messed up. Let's index the bases:

Original mRNA bases (index 1 - 15):
1: A, 2: U, 3: G, 4: U, 5: A, 6: U, 7: G, 8: A, 9: G, 10: A, 11: A, 12: U, 13: U, 14: A, 15: A.

Deleting G (index 3), new bases:
1: A, 2: U, 4: U, 5: A, 6: U, 7: G, 8: A, 9: G, 10: A, 11: A, 12: U, 13: U, 14: A, 15: A.

Now, reading frame (groups of 3, starting at 1):
Codon 1: 1 - 3: A, U, U (AUU)
Codon 2: 4 - 6: U, A, U (UAU)
Codon 3: 7 - 9: G, A, G (GAG)
Codon 4: 10 - 12: A, A, U (AAU)
Codon 5: 13 - 15: U, A, A (UAA)

Wait, that's not a shift? Wait, no—original AUG (1 - 3) is start codon. Deleting G (3) makes the first codon AU (1 - 2) + next base (4: U) → so codon 1: A U U (1 - 3), then codon 2: U A U (4 - 6) (which was original codon 2: UAU, but shifted by one base left? Wait, no, original codon 2 was UAU (4 - 6). After deleting G (3), the new codon 1 is 1 - 3 (A, U, U), codon 2 is 4 - 6 (U, A, U) → same as original codon 2? No, that can't be. Wait, maybe I made a mistake. Let's re-express:

Original codons: [AUG] [UAU] [GAG] [AAU] [UAA] (each 3 bases: positions 1 - 3, 4 - 6, 7 - 9, 10 - 12, 13 - 15).

Deleting G (position 3) → the sequence becomes: positions 1: A, 2: U, 4: U, 5: A, 6: U, 7: G, 8: A, 9: G, 10: A, 11: A, 12: U, 13: U, 14: A, 15: A.

Now, the reading frame is still 3 bases, but starting at position 1:

Codon 1: 1 - 3: A (1), U (2), U (4) → AUU

Codon 2: 4 - 6: U (4), A (5), U (6) → UAU (same as original codon 2? No, original codon 2 was UAU (4 - 6), but now codon 1 is 1 - 3 (A, U, U), so codon 2 is 4 - 6 (U, A, U) → same as original codon 2. Wait, that's not a frameshift? No, wait, the deletion is in the first codon, so the first codon is now 2 bases (AU) plus the first base of the next codon (U) → making AUU, then the rest shift? Wait, no—when you delete a base in the middle of a codon, the reading frame shifts for all subsequent codons. Wait, original first codon: AUG (3 bases). Delete G (third base), so first codon is AU (2 bases), then the next base is U (from UAU), so the new first codon is AUU (A, U, U), then the next codon is the next three bases: A (from UAU, second base), U (third base of UAU), G (first base of GAG) → AUG? Wait, no, let's list all bases after deletion:

Original: A U G U A U G A G A A U U A A

After deleting G (position 3): A U U A U G A G A A U U A A

Now, split into codons (3 per):

1: A U U…

Step 1: Analyze original codons

Original codons: AUG (1 - 3), UAU (4 - 6), GAG (7 - 9), AAU (10 - 12), UAA (13 - 15). Inserting a base between first (AUG) and second (UAU) codons (i.e., after position 3, before position 4).

Step 2: Determine new codon sequence

Let's say we insert a base, say X (any base, e.g., A, U, G, C). Now the base sequence becomes: A U G X U A U G A G A A U U A A. Now, the reading frame is shifted. The first codon is still AUG (1 - 3), then the next codon is X U A (4 - 6), then U G A (7 - 9), G A A (10 - 12), U U A (13 - 15), A (remaining, but UAA was the stop, now it's disrupted). So all codons after the insertion (from the second codon onwards) are shifted, as the reading frame (groups of 3) is now offset by 1 base. This changes the amino acid sequence of the protein (frameshift mutation), which can lead to a completely different protein, a truncated protein (if a stop codon is introduced early), or a non - functional protein.

Step 3: Conclusion for (b)

Inserting a base between the first and second codons causes a frameshift. The first codon remains AUG, but all subsequent codons (starting from the second) are shifted (e.g., original UAU becomes XUA, GAG becomes UGA, etc., depending on the inserted base), altering the amino acid sequence (frameshift mutation) and potentially affecting the protein's structure/function or causing it to be non - functional.

Answer:

s:
a) Deleting the G from the AUG codon causes a frameshift mutation. The first codon becomes AUU (instead of AUG), and all subsequent codons are shifted, altering the amino acid sequence. This can change the protein's structure/function or make it non - functional.

b) Inserting a base between the first and second codons causes a frameshift mutation. The first codon remains AUG, but all codons after the insertion are shifted, altering the amino acid sequence. This can lead to a different, truncated, or non - functional protein.