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biology question

hi, please could someone help me on this question? I identified that the 4th and 20th bases are A and T from left to right. However, after trying all possible options i found that neither 1,2 or 3 are correct however it says that all of the statements are correct? thank you in advance!

The table shows some of the genetic codes for amino acids:
genetic code amino acid coded for
(three-letter abbreviations)
AGA Arg
AGG Arg
ATG Met
CCC Pro
CCG Pro
CGA Arg
CTG Leu
GAC Asp
GGA Gly
GTC Val
GTG Val
TAG Stop (ends protein synthesis)
TGG Trp
TTA Leu
TTG Leu
The base sequence below shows the middle part of a gene coding for a protein:
A T G C G A G A C A T G T T A A G G T G G G A C C C C C G A G T C
Mutations took place in both the 4th and 20th base in this sequence.
Using only the information provided and reading the sequence from left to right, which of the
following statements could be correct for the resulting amino acid sequence after the two
mutations took place?

1 This sequence could be only six amino acids long.
2 The second amino acid in this sequence could be unaffected by the mutation.
3 This amino acid sequence could contain seven different amino acids.

A none of them
B 1 only
C 2 only
D 3 only
E 1 and 2 only
F 1 and 3 only
G 2 and 3 only
H 1, 2 and 3
Original post by Ashirs
hi, please could someone help me on this question? I identified that the 4th and 20th bases are A and T from left to right. However, after trying all possible options i found that neither 1,2 or 3 are correct however it says that all of the statements are correct? thank you in advance!

The table shows some of the genetic codes for amino acids:
genetic code amino acid coded for
(three-letter abbreviations)
AGA Arg
AGG Arg
ATG Met
CCC Pro
CCG Pro
CGA Arg
CTG Leu
GAC Asp
GGA Gly
GTC Val
GTG Val
TAG Stop (ends protein synthesis)
TGG Trp
TTA Leu
TTG Leu
The base sequence below shows the middle part of a gene coding for a protein:
A T G C G A G A C A T G T T A A G G T G G G A C C C C C G A G T C
Mutations took place in both the 4th and 20th base in this sequence.
Using only the information provided and reading the sequence from left to right, which of the
following statements could be correct for the resulting amino acid sequence after the two
mutations took place?

1 This sequence could be only six amino acids long.
2 The second amino acid in this sequence could be unaffected by the mutation.
3 This amino acid sequence could contain seven different amino acids.

A none of them
B 1 only
C 2 only
D 3 only
E 1 and 2 only
F 1 and 3 only
G 2 and 3 only
H 1, 2 and 3

have you written out the amino acids coded for by A T G C G A G A C A T G T T A A G G T G G G A C C C C C G A G T C ?
if you change the 4th base, what could be the resulting amino acid? how about for the 20th?

remember: after a "stop" codon, there will be no more amino acids put into the resulting sequence
Reply 2
Original post by bl0bf1sh
have you written out the amino acids coded for by A T G C G A G A C A T G T T A A G G T G G G A C C C C C G A G T C ?
if you change the 4th base, what could be the resulting amino acid? how about for the 20th?

remember: after a "stop" codon, there will be no more amino acids put into the resulting sequence


but aren't there various ways of changing it such as deletion which can change the entire sequence?
Original post by Ashirs
but aren't there various ways of changing it such as deletion which can change the entire sequence?


what about a substitution? for example a T changing to an A?

the question is just talking about "a mutation"... we don't know what the mutation is, we are just trying to work out whether any of the three statements could apply to the mutated sequence
Reply 4
Hi @bl0bf1sh
Thank you for your reply! I have a couple of questions. I have written out the sequence and attached a photo.
1) how can the sequence be only 6 amino acids long when there are 11 amino acids?
2) the second amino acid is CGA so how can it be unaffected as the mutation in the fourth base, A doesn’t code for an amino acid.
3) again, there are 8 different amino acids as I’ve written on the photo so how can there be 7?

Thank you so much!! image.jpg
Original post by Ashirs
Hi @bl0bf1sh
Thank you for your reply! I have a couple of questions. I have written out the sequence and attached a photo.
1) how can the sequence be only 6 amino acids long when there are 11 amino acids?
2) the second amino acid is CGA so how can it be unaffected as the mutation in the fourth base, A doesn’t code for an amino acid.
3) again, there are 8 different amino acids as I’ve written on the photo so how can there be 7?

Thank you so much!! image.jpg

For all the Australian people out there^^^
Original post by Ashirs
Hi @bl0bf1sh
Thank you for your reply! I have a couple of questions. I have written out the sequence and attached a photo.
1) how can the sequence be only 6 amino acids long when there are 11 amino acids?
2) the second amino acid is CGA so how can it be unaffected as the mutation in the fourth base, A doesn’t code for an amino acid.
3) again, there are 8 different amino acids as I’ve written on the photo so how can there be 7?

Thank you so much!! image.jpg


1) how can the sequence be only 6 amino acids long when there are 11 amino acids?
the question says that there is a mutation in the 20th base... try writing out the possibilities for the mutated codon, see what they code for (hint: see the "remember" bit in my first reply)

2) the second amino acid is CGA so how can it be unaffected as the mutation in the fourth base, A doesn’t code for an amino acid.
the codon CGA codes for the amino acid Arg. there is a mutation in the 4th base, so write out the possible mutated codons, and the amino acids they code for

3) again, there are 8 different amino acids as I’ve written on the photo so how can there be 7?
count how many different amino acids are coded for by the sequence you've written out :smile:

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