Video Transcript
As it is being replicated, DNA is
proofread to prevent errors being made. However, sometimes changes can
occur in a DNA base sequence. What are changes in the DNA base
sequence called? (A) Disruptions, (B) alterations,
(C) mutations, (D) transformations, (E) abrasions.
When DNA is replicated, or copied,
it is done so in a semiconservative way. This means that each original
strand acts as a template for the synthesis of a new strand. Let’s look at how DNA replication
can occur starting from that original double-stranded molecule.
During DNA replication, the two
strands of DNA are separated by an enzyme called DNA helicase. Now that it’s separated, we’ll also
include the four DNA bases: guanine as shown in orange, cytosine as shown in blue,
adenine as shown in green, and thymine as shown in pink. Once these two strands are
separated, the single-stranded molecules can be copied. The enzyme that does this is called
DNA polymerase.
DNA polymerase moves along the
original strand and uses it as a template by adding complementary nucleotides to the
new strand. However, sometimes errors are made,
as we can see here, where a thymine was added instead of a cytosine. This can be corrected by the
proofreading function of DNA polymerase, where it removes the incorrect nucleotide
and puts the right one in its place. This process continues until both
strands of DNA are replicated. Here, we can see the two new
strands and the two original strands.
Despite the proofreading function
of DNA polymerase, errors can still occur that aren’t corrected. We can see this here with cytosine
being incorrectly paired with adenine. These errors can remain in the
sequence of DNA and are known as mutations. Therefore, changes in the DNA base
sequence are given by answer choice (C), mutations.
