Video Transcript
A sequence of DNA is transcribed
into an RNA sequence. This RNA sequence reads from five
prime to three prime GCUUUCACGCAC. Use the codon wheel provided to
determine the sequence of amino acids. Arginine, serine, threonine,
proline. Serine, leucine, alanine,
histidine. Alanine, phenylalanine, threonine,
histidine. Serine, leucine, alanine,
glutamine. Or alanine, leucine, threonine,
glutamine.
This question is asking us about
how to translate a sequence of mRNA into the corresponding amino acids. Before we can answer this, let’s
clear the answer choices and review some key points.
Let’s say our cell here needs to
produce insulin. The gene for insulin is located
here in pink in the cell’s DNA. In order for this cell to produce
insulin or any other protein, it must go through two processes called transcription
and translation. During transcription, the gene for
the protein is transcribed or copied to produce what’s called messenger RNA or
mRNA. This messenger RNA is a message for
the cell that tells it that it needs to make the protein, or insulin in this
case.
Transcription is the process of
converting a section of double-stranded DNA or our insulin gene shown here in pink
into a single-stranded mRNA molecule. Like DNA, the sequence for mRNA is
written in the five-prime to three-prime direction and contains four different
nucleotides or bases: adenine or A for short, guanine, cytosine, but instead of
thymine, which is in DNA, RNA uses uracil or U for short.
After transcription, the sequence
in the mRNA molecule can be translated into its corresponding amino acids. This step is called translation,
and it forms a polypeptide with each of these colored circles representing a
different amino acid. This polypeptide can then fold to
form its corresponding protein, or insulin in this example.
Now that we’ve covered
transcription and translation, let’s turn our attention to this mRNA sequence in the
question and describe how this specific sequence can be translated into amino
acids.
An mRNA sequence is translated in
groups of three nucleotides called a codon. A codon is a sequence of three
nucleotides that code for an amino acid. Codons are always read in a way
that they’re not overlapping. So, in this sequence, this is the
first codon, this is the second codon, this is the third codon, and here’s the last
codon. So, this mRNA sequence has four
codons.
Now, in order to translate the
sequence of nucleotides into its corresponding amino acid, we need to use a codon
wheel, like the one shown on the left. To use the codon wheel, we start
from the inside. This corresponds to the five-prime
end of the codon. And we work our way outwards to the
three-prime end of the codon. So for this codon, we’ll be working
from the five-prime to the three-prime end.
So, with the codon GCU, we start
with G, then we move over to C, and finally we land on U. So, the codon GCU corresponds to
the amino acid alanine. Then, for the next codon UUC, we do
the same thing. So, the first nucleotide is U, then
U again, and then C. This corresponds to the amino acid
phenylalanine. Then, for the codon ACG, this
corresponds to threonine. And finally, the codon CAC
corresponds to the amino acid histidine. Therefore, the corresponding amino
acid sequence for the given mRNA sequence is alanine, phenylalanine, threonine, and
histidine.
