Video Transcript
In the process used by gene
machines, oligonucleotides are formed. What is an oligonucleotide? (A) A strand of DNA formed from a
strand of mRNA, catalyzed by reverse transcriptase. (B) A sequence of amino acids that
code for the desired gene. (C) A naturally occurring section
of DNA. (D) A synthetically produced short
strand of DNA or RNA. Or (E) a section of DNA removed
from a genome by restriction enzymes.
In this question, we’re being asked
about oligonucleotides, which are involved in the process used by gene machines to
synthesize genes. Let’s quickly review the concepts
behind gene machines.
A gene machine is used to
synthesize a gene. A gene is a stretch of DNA
nucleotides whose sequence forms the code required to synthesize a specific
functional unit, like a protein.
You might remember learning about
the central dogma of molecular biology, which states how DNA is transcribed into
mRNA, which is then translated into an amino acid sequence that forms a protein. In order to synthesize a gene for a
particular protein, a gene machine must be provided with the sequence of nucleotides
needed. In order to synthesize a gene with
the required sequence, the gene machine uses short sequences called
oligonucleotides. An oligonucleotide is a
synthetically produced single-stranded stretch of DNA or RNA. The word part oligo- is the Greek
word that means few, emphasizing that this strand is only made up of a few
nucleotides.
Let’s say our gene machine is being
used to synthesize a gene that should look like this. The gene machine will use two
oligonucleotides to begin the synthesis process. One might look something like
this. The other might look like this. As you can see, the two
oligonucleotides are chosen so that they provide an overlapping region of
double-stranded DNA, as well as two single-stranded overhangs. The gene machine can then use an
enzyme called Taq polymerase to fill in the gaps and synthesize the complete
sequence.
Let’s see if we can have a go at
filling in the sequence the way Taq polymerase would. If we begin with the upper strand,
we can use the nucleotide sequence from the lower strand to figure out the
complementary nucleotides needed. Similarly, we can fill in the lower
strand by using the complementary nucleotides of the upper strand. Now we have the complete
double-stranded DNA sequence that makes up the gene. We can use what we’ve learned about
gene machines and oligonucleotides to answer our question. An oligonucleotide would be best
described as (D): a synthetically produced short strand of DNA or RNA.
