Video Transcript
Which of the following correctly
describes the features of the genetic code? (A) It is degenerate, universal,
and nonoverlapping. (B) It is degenerate, organism
specific, and nonoverlapping. (C) It is universal, organism
specific, and nonrepeating.
In order for a gene in DNA to be
converted into a protein, it needs to go through a couple of steps. The first step is called
transcription and involves the DNA being copied to form mRNA. Then, this mRNA sequence is
translated into a sequence of amino acids to form a polypeptide. This polypeptide can then go on to
fold into a protein. Since this question is asking about
the genetic code, let’s describe how a sequence of mRNA can be translated into amino
acids.
A group of three nucleotides in
mRNA is called a codon. In this nine-nucleotide sequence of
mRNA, there’s three codons. The specific sequence of a codon
corresponds to a specific amino acid. And we can use a codon wheel to
figure this out. When reading a sequence of mRNA, we
start from the five prime end and work our way to the three prime end.
In the codon wheel, we’re doing the
same thing, by starting from the center, which corresponds to the five prime end,
and working our way out toward the three prime end. So the codon CCA gives us the amino
acid proline. The codon GUA gives us the amino
acid valine. And the codon AGG gives us the
amino acid arginine. These codons and how they’re
decoded into amino acids, as we’ve just demonstrated using this codon wheel,
corresponds to the genetic code.
Now that we’ve introduced the
genetic code, let’s go over some of its features in order to answer our
question.
The first feature that we’ll cover
is that it’s degenerate, meaning that multiple codons can code for the same amino
acid. If we look at the amino acid
serine, we can see that it’s coded by four different codons: UCU, UCC, UCA, and
UCG.
Another feature is that this
genetic code is universal. The codon CCA codes for proline in
humans, in chickens, in bacteria, and so on. It is universal to all life on
Earth.
And the last feature we’ll discuss
is that the genetic code is nonoverlapping. Codons are translated as
consecutive nucleotide triplets, as we’ve shown here, where one codon follows
another. Codons do not overlap as they do
here.
Getting back to our question, the
option that correctly describes the features of the genetic code is given by answer
choice (A). It is degenerate, universal, and
nonoverlapping.
