LESSON 2: DNA
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cells must replicate their
prior to cell division. This assures that each new cell
produced receives all of the genetic material necessary to
survive and reproduce. As organisms have from thousands to
millions or even billions of base-pairs of DNA, this process
could seem overwhelmingly complicated. However, cells
utilize a relatively simple mechanism to copy their DNA
rapidly and accurately. Several different
are involved in this process - some unwind the DNA from its
double helix, some separate the two strands of DNA, and some
build new strands of DNA complementary to each of the
original strands. After the DNA is replicated, cells employ
several other enzymes to ‘proofread’ their work and correct
mistakes from the replication process. The end result of DNA
replication is two complete and accurate copies of a cell’s
DNA. These copies may then be partitioned into daughter
cells during cell division.
Understand the basic mechanism of
DNA replication, and know the various enzymes that play a
role in this process.
Be familiar with several of the
repair mechanisms utilized by cells to correct errors in
Topics covered in this Lesson
When cells replicate their DNA, they
make two identical copies of their DNA from one original copy.
Each new copy has one ‘parent’ strand of DNA and one
newly-synthesized strand. The process of DNA replication
involves several different types of
enzymes. Some enzymes unwind the DNA, others
build new strands of DNA, and yet others are involved in the
finishing steps, including proofreading of the new DNA. While
there are a few differences between prokaryotic and eukaryotic
DNA replication, the processes are largely the same, and utilize
many of the same enzymes.
DNA replication must occur before any
type of cell division, whether the cell is prokaryotic or
eukaryotic. DNA replication assures that any daughter cells
produced will have a complete copy of the DNA necessary for the
cell to survive.
Be able to describe the pattern
of events that happen during DNA replication.
Understand the pattern of
complementary base-pairing that occurs between each
strand of DNA.
Know why is DNA replication
referred to as
Know what an origin of
replication is and what role it plays in DNA
Be familiar with the different
enzymes involved in DNA replication and their roles.
Understand the role do RNA
primers play in DNA replication.
Describe why the
anti-parallel nature of DNA presents a challenge for DNA replication
and how cells solve this problem.
is essential that
DNA replication is accurate. Mistakes made during the copying of
DNA could completely disrupt important genes, leading to problems or
even death for a cell or organism. Fortunately,
DNA polymerase is does a very accurate job synthesizing new
strands of DNA, inserting an incorrect base on average only once in
every ten thousand to one million bases. Cells also utilize several
other repair processes and enzymes to bring their mistake rate even
lower, and insure that their DNA is replicated accurately.
Know and understand the three
basic repair mechanisms cells employ to correct errors
in DNA replication.
Understand why it is important
for cells to accurately copy their DNA.
Be able to discuss the
evolutionary significance of a low error rate in DNA