Here is the full question:
An example of a portion of the T4 rIIB gene in which Crick and Brenner had recombined one "+" and one "-" mutation is shown below. The RNA-like strand of the DNA is shown with 5' conventionally on the left. What alterations in amino acids occurred in this double mutant (which, by the way, produces wildtype plaques)? List any changed amino acids in order 1 through 7 with spaces between them. Use the standard 3 letter codes for the amino acids but enter the word "same" if the amino acid is the same in the wild type and the mutant protein (e.g. same lys gln same same same pro).
Wildtype sequence
AAA AGT CCA TCA CTT AAT GCC
Mutant sequence
AAA AAG TCC ATC ATT AAT GCC
So I deduced that the complement mRNA sequence for the wildtype is:
UUU UCA GGU AGU GAA UUA CGG
giving the amino acid sequence:
phe ser gly ser glu leu arg
For the mutant:
UUU UUC AGG UAG UAA UUA CGG
with amino acid sequence:
phe phe arg stop stop leu arg
So I put in the answer:
same phe arg
and got it wrong, so I also put in:
same phe arg stop stop same same
and got it wrong. What am I doing?
An example of a portion of the T4 rIIB gene in which Crick and Brenner had recombined one "+" and one "-" mutation is shown below. The RNA-like strand of the DNA is shown with 5' conventionally on the left. What alterations in amino acids occurred in this double mutant (which, by the way, produces wildtype plaques)? List any changed amino acids in order 1 through 7 with spaces between them. Use the standard 3 letter codes for the amino acids but enter the word "same" if the amino acid is the same in the wild type and the mutant protein (e.g. same lys gln same same same pro).
Wildtype sequence
AAA AGT CCA TCA CTT AAT GCC
Mutant sequence
AAA AAG TCC ATC ATT AAT GCC
So I deduced that the complement mRNA sequence for the wildtype is:
UUU UCA GGU AGU GAA UUA CGG
giving the amino acid sequence:
phe ser gly ser glu leu arg
For the mutant:
UUU UUC AGG UAG UAA UUA CGG
with amino acid sequence:
phe phe arg stop stop leu arg
So I put in the answer:
same phe arg
and got it wrong, so I also put in:
same phe arg stop stop same same
and got it wrong. What am I doing?
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Wildtype sequence
5'-AAA AGT CCA TCA CTT AAT GCC-3' (sense strand)
Lys-Ser-Pro-Ser-Leu-Asn-Ala
Mutant sequence
5'-AAA AAG TCC ATC ATT AAT GCC-3' (sense strand)
Lys-Lys-Ser-Ile-Ile-Asn-Ala
Whoa. There was a frameshift that then got fixed.
Where you went wrong (in two different ways!) was in your RNA. You were given the "sense" strand of DNA written 5' first, so it has the same directionality and sequence (with T replaced by U) as the mRNA. So you don't need to do a complement at all. Get it?
P.S. Whoever picked a font that has the same shape for lowercase L as for uppercase i for Yahoo Answers sucks. Same for not letting us use a fixed-spacing font.
5'-AAA AGT CCA TCA CTT AAT GCC-3' (sense strand)
Lys-Ser-Pro-Ser-Leu-Asn-Ala
Mutant sequence
5'-AAA AAG TCC ATC ATT AAT GCC-3' (sense strand)
Lys-Lys-Ser-Ile-Ile-Asn-Ala
Whoa. There was a frameshift that then got fixed.
Where you went wrong (in two different ways!) was in your RNA. You were given the "sense" strand of DNA written 5' first, so it has the same directionality and sequence (with T replaced by U) as the mRNA. So you don't need to do a complement at all. Get it?
P.S. Whoever picked a font that has the same shape for lowercase L as for uppercase i for Yahoo Answers sucks. Same for not letting us use a fixed-spacing font.
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Your wt DNA looks like this:
5'-AAA AGT CCA TCA CTT AAT GCC-3'
3'-TTT TCA GGT AGT GAA TTA CGG-5'
So when transcription happens using the bottom as the template, the mRNA looks exactly like the top strand of DNA, except for U's instead of T's.
You way was using the top strand as the template, and then you didn't flip it around to 5'->3'.
ALWAYS flip to 5' -> 3'
When you translate AAA AGU CCA UCA CUU AAU GCC, you get KSPSLNA, which is what T4 really has.
5'-AAA AGT CCA TCA CTT AAT GCC-3'
3'-TTT TCA GGT AGT GAA TTA CGG-5'
So when transcription happens using the bottom as the template, the mRNA looks exactly like the top strand of DNA, except for U's instead of T's.
You way was using the top strand as the template, and then you didn't flip it around to 5'->3'.
ALWAYS flip to 5' -> 3'
When you translate AAA AGU CCA UCA CUU AAU GCC, you get KSPSLNA, which is what T4 really has.