Gene to Protein Part 3 VoiceThread Transcript
Slide 1
This question provides you with a DNA sequence and asks you to
determine the sequence of amino acids for which it codes.
Slide 2
To answer the question, you must first transcribe the
information in the DNA into the complementary messenger RNA. Then use
the genetic code to determine the appropriate amino acids.
The mRNA is 5' AUG GCC AGA 3'. The amino acids are met - ala - arg.
Slide 3
This question gives you the amino acids and asks to you determine
which of the following DNA sequences code for these amino acids.
Slide 4
The first step is to determine the mRNA sequence based on the
amino acid sequence.
The amino acid asparagine is abbreviated asn - it has two possible codons AAU or AAC - I indicated the second possible codon by putting the C in parentheses.
The amino acid trptophan - abbreviated trp - has only one possible codon - UGG.
The amino acid methionine has only one possible codon - AUG.
The amino acid cysteine has two possible codons - UGU or UGC.
Slide 5
The next step is to determine which of the possible answers
provides the DNA that codes for this mRNA sequence.
We can quickly discount option A - there are Us in the sequence so this is an RNA molecule and not a DNA molecule.
We have to remember to align the polarities - so the 5' end of the mRNA must align with the 3' end of the DNA. We also have to remember the base pairing rules.
Slide 6
Using these rules - we can determine that B is the correct
answer. The 5' end of the mRNA aligns with the 3' end of the DNA in
option B. Then the base pairing rules show us that A pairs with T, A
with T, C with G, and so on.
Slide 7
This question asks you to use the genetic code to determine a gene
mutation that causes labrador retriever dogs to be yellow rather than black or
brown.
You are given the mRNA of both the normal gene and the mutated gene.
Slide 8
The first step is to determine the sequence of amino acids in the
normal protein. We can read the genetic directly from the mRNA.
Slide 9
Reading the mRNA we get the amino acid sequence
serine,glutamine (gln), glutamic acid (glu), leucine, arginine, and lysine.
Our next step is to find the difference between the normal gene and the
mutated gene.
The difference is that the mutated gene has a U instead of a C in this position.
Knowing the difference - we can determine the effect the mutation will have on the protein. The codon CGA has been changed into the codon UGA. So instead of an arginine - the mRNA now codes for a stop codon.
Slide 10
The result is that the mutated protein is too short - it thus
does not code for a functional pigment molecule and the dog that inherits this
allele has yellow fur.
Slide 11
This last question gives you a tRNA anticodon and asks to
determine the template DNA.
Slide 12
To answer this question, you need to determine the mRNA codon
that is complementary to the tRNA anticodon. The complementary mRNA is
5' CAU 3'. From the mRNA you can determine the DNA - 3' GTA 5' and the
amino acid - the mRNA codon CAU codes for the amino acid histidine.
Slide 13
So the correct answer to this question is D.
Please let me know if you have any questions.