POGIL Cell Biology Activity 6 – DNA Replication
MODEL 1:
Schivell
"Replication
Bubble"
The circle is an E. coli chromosome at the
beginning of DNA synthesis. The original
DNA strands are called "parental strands".
In this model, DNA is black and RNA is gray.
Each shape represents a different enzyme.
"replication fork"
T
I
M
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POGIL Cell Biology Activity 6 – DNA Replication
Schivell
1. Which parental strand acts as a template for synthesis of a new complementary DNA
strand?
- neither strand
- both strands
- only one strand
2. a. Label the 5' and 3' ends of the new strands in the middle panel of Model 1.
b. On what end of a DNA strand are new nucleotides added? _________
c. Draw a sketch of what a nucleotide should look
like before it is added to the new strand by a polymerase:
3. a. Match each enzyme's shape with its function and fill in the column on the left.
Shape:
Function:
Enzyme that synthesizes the largest part of
the new DNA strands
Enzyme that forms a phosphodiester bond
without adding a new nucleotide
Enzyme Name:
Enzyme that synthesizes a short RNA primer
Enzyme that replaces RNA nucleotides with
DNA
Enzyme that breaks H-bonds between strands
of the parent DNA helix
b. Use the following root "translations" fill in the blanks with the enzyme names:
Roots:
Enzyme names:
- "lig-" is a latin prefix meaning "bind" _______________________
- DNA polymerase
- helicase
- "prim-" is a latin prefix meaning "first" _______________________
- ligase
- primase
- "poly-" means "many", "-mer" is "unit" _______________________
- "heli-" means "coil or spiral" _____________________
c. Fill in the Enzyme Name column in the table above with one of the enzymes. One enzyme
will be used twice.
d. Go back and label the shapes on the model with their enzyme names.
e. The enzyme that does the majority of DNA synthesis is called DNA polymerase III. The
enzyme that replaces RNA nucleotides with DNA is called DNA polymerase I. Add I and III
in the table above and in the model.
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POGIL Cell Biology Activity 6 – DNA Replication
Schivell
4. DNA polymerase can add nucleotides using the bottom strand as a template in the diagram
below on the left, but cannot add nucleotides using the bottom strand as a template in the
diagram on the right.
DNA polymerase can use this:
but not this:
a. Think back to transcription. Can RNA polymerase use only one or
can it use both of the templates above when adding nucleotides? ________
b. Write out in words what RNA polymerase can do that DNA polymerase cannot, based on
your answer for 'a'.
5. a. Over time, one new DNA strand at each replication fork is made in pieces, while the other
one is made continuously. Explain why this has to be the case in 1-2 sentences.
b. In the middel panel of Model 1, label the continuously made strand the "leading strand".
Label the strand made in pieces the "lagging strand".
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POGIL Cell Biology Activity 6 – DNA Replication
Schivell
MODEL 2: This model shows one entire eukaryotic linear chromosome. The original
chromosome is shown before replication. The same chromosome is shown about 30 minutes
after the process of DNA synthesis has begun in each of four different cells (no enzymes are
shown). The chromosomes are aligned by sequence and gray = new DNA.
"original"
chromosome
cell #
1
2
3
4
6. Based on Model 2, choose the statement below that BEST fits the data above.
_____ DNA synthesis can start anywhere on a chromosome.
______ DNA synthesis starts only at one place on a chromosome.
______ DNA synthesis starts at specific locations on a chromosome.
______ DNA synthesis starts at every location at exactly the same time.
7. Using stars, indicate the specific locations where synthesis can start on the original
chromosome. These are called "Origins of Replication"
8. a. The protein that binds to origin sequences is called an "initiator protein". Do you think
that initiator proteins are expressed constitutively? Why or why not?
b. What is the most likely role of initiator proteins? (Circle the BEST answer)
- Synthesize new DNA strands
- Unwind the DNA parental strands
- Join fragments of newly made DNA
- Recruit (bring in) the complex of DNA replication enzymes
9. In transcription and translation, the terminator and stop codons were used (respectively) to
end the processes at the correct location. Keeping in mind the goal of DNA replication, what
do you think stops the process of DNA synthesis?
10. When do cells need to replicate their DNA? ______________________________________
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POGIL Cell Biology Activity 6 – DNA Replication
Schivell
On Your Own:
1. Watch the videos marked "Replication.mov" on our website under the "Movies" link. You
may need to watch them several times to get a sense of how the replication enzymes work
together at a replication fork.
In the Replication.mov video:
a. Which part of the DNA is phosphodiester backbone, red or yellow? _________
b. Which part of the DNA represents the nitrogenous bases, red or yellow? _________
c. Determine which strand is the leading strand and which is the lagging strand.
d. Try to identify as many enzymes as possible in the animation.
2. A cartoon of one replication bubble is shown below. On one template strand on one fork,
the newly made strands are shown. Draw in the rest for the rest of the bubble and label the 3'
and 5' ends as well as the leading and lagging strands. (Arrow indicates 3' end)
3. Drawn in detail below is a region of parental DNA with two replication forks approaching
from either direction. Explain what enzymes will be needed and diagram how the replication
will be completed when the two forks meet.
4. On planet Mandoid, DNA polymerase III adds nucleotides onto the 3’ end of a growing
nucleic acid just like on Earth. However, Mandoid DNA polymerase III CAN start a new
DNA strand on its own (it does not need an existing 3’ end to add to).
5’
3’
5’
3’
a. The diagram above shows a single replication fork of a chromosome on Mandoid. Draw
and label the leading and lagging strands. Include 5’ and 3’ labels!
b. Which of the following enzymes or molecules involved in DNA replication on Earth will
ALSO be found on planet Mandoid? (Circle ALL that apply)
- DNA pol I
- ligase
- primase
- helicase
5. E. coli, a prokaryote, has a single origin of replication on its one chromosome. The E. coli
chromosome is about 5 million base pairs long. Human chromosomes are on average 20 times
longer. Do you think human chromosomes have a single origin or many? Why?
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