Chapter 1. Chapter 12 Branched Tutorial: Replication
1.1 Problem Statement
The following diagram represents the template strands of a replication bubble in a DNA molecule. You will need to correctly provide the locations and directions of components relating to the new strands which will be produced.
Question
From the choices below, select the diagram which shows the correct labeling for each of the following features: the direction of unwinding; 5′ and 3′ ends of the new strands; leading strands; lagging strands; Okazaki fragments; and RNA primers. (Note: the newly synthesized strands are shown in red.)
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I.
1.2 Step 1: Understanding the problem
Question
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There are some key words in the Problem Statement that should help you determine the topic. Which process involves making a new copy of the DNA molecule?
Question
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The question asks about the process of DNA synthesis. Focus on the necessary components that would be needed to accurately explain the process of DNA replication.
1.3 Step 2: Identifying the proper 5′ and 3′ directions
Question
1. Which of the following diagrams displays the proper labeling of the 5′ and 3′ directions for each newly synthesized strand of DNA?
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B.
C.
D.
Instant TA
The strands of a DNA molecule have polarity or directionality—if one end of the strand is 5′, then the other end of the strand must be 3′. The strands will be antiparallel, or in opposite directions to each other.
Question
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The antiparallel nature of DNA describes the direction or polarity of the two nucleotide strands.
Question
3. Use the dropdown menus to show the proper polarity of the newly synthesized strands.
| A. 6FvR25S5bTqSpEn4Bt+R5A== | B. +vt7Amo9toACyf4Z8odItw== |
| C. +vt7Amo9toACyf4Z8odItw== | D. 6FvR25S5bTqSpEn4Bt+R5A== |
Instant TA
The strands of a DNA molecule have polarity or directionality – if one end of the strand is 5′, then the other end of the strand must be 3′. The strands will be antiparallel, or in opposite directions to each other.
1.4 Step 3: Determining the direction of replication
Question
1. Which of the following diagrams displays the proper labeling of the 5′ and 3′ directions for each newly synthesized strand of DNA?
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B.
C.
D.
Instant TA
New nucleotides are always added to the free 3′ hydroxyl group of a DNA molecule.
Question
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New nucleotides are always added to the 3′ end of the newly synthesized strand.
Question
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Instant TA
During DNA synthesis, new nucleotides are added to the 3′ end of the newly synthesized strand.
Question
4. On the diagram below, select the proper directions for the arrows on the newly synthesized strands to indicate the correct direction of replication.
| A. RobSGUV/oIlHisbDCW7EWw== |
| B. MQT6XMoYQc5460y9O4V4vQ== |
Instant TA
DNA synthesis occurs in a 5′ to 3′ direction. The new nucleotides are added at the 3′ end of the new DNA molecule during the synthesis process.
1.5 Step 4: Unwinding of the DNA
Question
1. Select the diagram below that has the correct direction of the unwinding of the DNA as well as the leading and lagging strands labeled properly.
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Instant TA
Since new nucleotides are added at the 3′ end of a new DNA molecule, the template strand must unwind to allow for continued addition of nucleotides to the 3′ end. Continuous replication can only occur with leading strand synthesis.
Question
2. On the diagram below, indicate the direction that the double-stranded DNA is unwinding at each replication fork by choosing the correct label from the associated dropdown menus.
| A. GzSD2wDm2yB8J7iUVFaucGaLYF+IUJzUCNywGjEG8rJJpc7Q | B. AWCaVTBtYyDFN8wa994UdbCv9L71OxgbvJlEHZg/gfukxmG9 |
Instant TA
Initiation of replication will begin at an origin in the middle of the replication bubble. The template DNA will unwind outward from the origin in both directions.
Question
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Continuous replication requires only a single initiation. Look at each fork and determine whether the direction of replication for a strand is the same as the direction of unwinding. The strand on which replication is in the same direction as unwinding is the leading strand; here replication can proceed continuously as the DNA unwinds. The strand on which replication is in the direction opposite that of unwinding is the lagging strand; here replication occurs discontinuously because replication is occurring away from the replication fork. Each replication fork should have one leading strand and one lagging strand.
Question
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Instant TA
Discontinuous replication occurs in short segments.
Question
5. On the diagram below, indicate the leading and lagging strands by using the dropdown menus for each box.
| A. Goz6gGeWFdmFTqswEKESPEENVr0jieLH | B. Vi8F0cyvpJjHI6aMXkPt6mXxU+lqJJcx |
| C. Vi8F0cyvpJjHI6aMXkPt6mXxU+lqJJcx | D. Goz6gGeWFdmFTqswEKESPEENVr0jieLH |
Instant TA
Replication on the leading strand occurs in the same direction as unwinding of the DNA molecule. Replication on the lagging strand occurs in the opposite direction as unwinding of the DNA molecule. Each replication fork has one leading strand and one lagging strand.
1.6 Step 5: Locating the Okazaki fragments and RNA primers
Question 1.1
1. Choose the diagram that is properly labeled.
A.
B.
C.
D.
Instant TA
Okazaki fragments are short stretches of DNA that are created during discontinuous replication on the lagging strand. An RNA primer is required to initiate DNA synthesis. On the lagging strand, there will be one RNA primer at the beginning (5′ end) of each Okazaki fragment. There will be a single primer at the beginning (5′ end) of the leading strand.
Question 1.2
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Instant TA
Okazaki fragments are short segments of DNA that are synthesized discontinuously.
Question 1.3
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RNA primers are synthesized by primase during replication and initially serve as the starting point for the addition of new nucleotides during strand synthesis.
Question 1.4
4. Which numbers on the diagram below signify the correct placement of Okazaki fragment labels?
Instant TA
Okazaki fragments are short stretches of newly synthesized DNA that occur because of accessibility limitations to the template strand during the unwinding process.
Question 1.5
5. Which of the letters below represent places where RNA primers would be found? Select YES if the letter is displayed at a location where an RNA primer would be found, or select NO if the letter is displayed at a location where an RNA primer would not be found.
| A AD2YBdbb6x3kfgtembjVpQ== | E Efx3eLtX1Ia8xzC/fjL6GA== | I Efx3eLtX1Ia8xzC/fjL6GA== |
| B AD2YBdbb6x3kfgtembjVpQ== | F Efx3eLtX1Ia8xzC/fjL6GA== | J Efx3eLtX1Ia8xzC/fjL6GA== |
| C Efx3eLtX1Ia8xzC/fjL6GA== | G Efx3eLtX1Ia8xzC/fjL6GA== | K Efx3eLtX1Ia8xzC/fjL6GA== |
| D Efx3eLtX1Ia8xzC/fjL6GA== | H AD2YBdbb6x3kfgtembjVpQ== | L AD2YBdbb6x3kfgtembjVpQ== |
Instant TA
RNA primers will be found at the 5′ ends of the newly synthesized DNA fragments.
1.7 Step 6: Solving the Problem
Question
Now that you have reviewed some details, let’s try the initial problem again. From the choices below, select the diagram which shows the correct labeling for each of the following features: the direction of unwinding; 5′ and 3′ ends of the new strands; leading strands; lagging strands; Okazaki fragments; and RNA primers. (Note: the newly synthesized strands are shown in red.)
A.
B.
C.
D.
E.
F.
G.
H.
I.
Instant TA
If you are unsure of the answer, go back and review some of the earlier steps that you worked through for this problem.