Questions and Answers
Classify each item according to its role in DNA replication:
Parental DNA strands = Serves as a template for a new DNA molecule Nucleoside triphosphates = Building blocks needed to assemble a new DNA molecule DNA primase, DNA gyrase, DNA polymerases, DNA ligase, DNA helicase = Enzymes required to replicate DNA Nucleoside monophosphates, Ribose = Not directly required for DNA replication
Match each enzyme with its function in E. coli:
DNA Pol III = Main replication enzyme; responsible for bulk of DNA synthesis DNA Pol I = Acts on lagging strand to remove RNA primers and replace them with DNA DNA Pol II = Involved in DNA repair, not in replication
If 28% of the DNA nucleotides from a certain organism contain the base T, what percent will contain the base G?
22
What is the correct structure of DNA monomers?
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Why do complementary nucleotides across the double-stranded DNA bond together using hydrogen bonds rather than covalent bonds?
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According to Chargaff's rule, A = T and C = G and A + G = C + T.
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Why is the replication machinery found at the replication fork?
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Based on your knowledge of the structure of DNA, why is it more likely for a G to mutate to an A than to a C or a T?
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Which of the following synthesizes the daughter strands during DNA replication?
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Why is the lagging strand synthesized in a discontinuous fashion?
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Arrange the following proteins in the proper order in which they participate in DNA replication:
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What is required to replicate the lagging strand of DNA?
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RNA primers are removed by the action of which enzyme?
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If DNA polymerase III could add nucleotides in either direction, Okazaki fragments would no longer form.
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The enzyme that unwinds a segment of the DNA molecule is?
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How do DNA polymerase I and DNA polymerase III differ?
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What is unique about telomerase?
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Which of the following best describes the function of telomerase at the telomere?
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Based on his experiments with the bacterium S. pneumoniae, what conclusion did Griffith reach?
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What did Avery, MacLeod, and McCarty determine as the substance responsible for converting live, nonvirulent bacteria into live, virulent bacteria?
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What did Hershey and Chase use to demonstrate that DNA is the genetic material of phages?
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Because the 2 strands of a DNA molecule run in opposites, they are said to be bidirectional.
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DNA polymerases can add new DNA nucleotides only to the 5' end of an existing strand.
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Because the 2 strands of a DNA molecule run in opposite directions, and because DNA polymerases can synthesize new strands only in the 5' to 3' direction, polymerases on opposite strands must synthesize DNA in opposite directions.
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The DNA strand that grows away from the replication fork is synthesized continuously from one initial primer.
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The DNA strand that grows toward the replication fork is synthesized discontinuously in short pieces called Okazaki fragments.
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Each Okazaki fragment has its own primer.
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The DNA strand that is synthesized continuously is called the lagging strand.
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The DNA strand that is synthesized discontinuously is called the leading strand.
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DNA ligase joins adjacent Okazaki fragments together into a complete strand.
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DNA polymerases cannot initiate synthesis of a new DNA strand; they can only add bases to an existing strand.
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Which characteristic of DNA allows each strand of the molecule to act as a template that specifies the exact sequence of nucleotides in the other strand?
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Many DNA polymerases have 3'-to-5' exonuclease activity that allows 'proofreading' and replacement of incorrect bases.
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Proofreading effectively eliminates all errors during DNA replication.
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Although most mutations are harmful, some may be beneficial.
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Error correcting mechanisms during DNA replication cause cells to accumulate errors at a higher rate, which leads to higher levels of deleterious or lethal mutations.
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In addition to errors that occur during DNA replication, cells are constantly exposed to agents that can damage DNA, such as UV light, X-rays, and chemicals in the environment.
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Agents that damage DNA can lead to mutations.
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Any agent that decreases the number of mutations below background levels is called a mutagen.
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Cells cannot escape exposure to mutagens, but they have evolved systems that enable them to repair all of the damage.
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When does DNA replication in bacteria begin?
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How is bacterial DNA replication different from eukaryotic DNA replication?
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What can be concluded about an organism if genetic analysis indicates it contains the gene that codes for telomerase?
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Study Notes
DNA Replication Roles and Components
- Parental DNA strands act as templates for new DNA synthesis.
- Nucleoside triphosphates are the building blocks essential for assembling new DNA.
- Key enzymes in DNA replication include DNA primase, gyrase, polymerases, ligase, and helicase.
- Nucleoside monophosphates and ribose are not required for the DNA replication process.
Enzymes in E. coli
- DNA Pol III is the primary enzyme for DNA synthesis during replication.
- DNA Pol I removes RNA primers on the lagging strand and replaces them with DNA.
- DNA Pol II participates in DNA repair, not in replication.
Base Composition and Chargaff's Rule
- If 28% of nucleotides contain Thymine (T), then 22% will contain Guanine (G).
- Chargaff's rule stipulates that in double-stranded DNA, Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G).
DNA Structure and Mutations
- DNA monomers consist of a phosphate-sugar-base structure.
- Hydrogen bonding between complementary nucleotides allows for easy separation during replication, unlike strong covalent bonds.
- Similar structural properties between Guanine (G) and Adenine (A) make mutations from G to A more likely than to C or T.
Replication Process
- The replication machinery operates at the replication fork to access leading and lagging strands and stabilize template DNA.
- DNA polymerase is responsible for synthesizing daughter strands during replication.
- The lagging strand is synthesized discontinuously due to the 5' to 3' synthesis constraint.
Protein Order in DNA Replication
- The correct sequence of protein involvement in DNA replication is helicase, single-strand binding proteins, primase, and DNA polymerase I.
- Okazaki fragments, along with primase and DNA ligase, are essential for lagging strand synthesis.
Unique Features and Functions
- Telomerase has an RNA molecule and adds new DNA to the telomere overhang.
- Transformation is the process established by Griffith, where genetic information transfers from dead virulent to live nonvirulent cells.
- Avery, MacLeod, and McCarty identified DNA as the substance responsible for virulence changes.
Heritage of Genetic Material
- Hershey and Chase demonstrated that DNA is the genetic material in phages using radioactively labeled components.
- DNA strands run antiparallel, which means they are not bidirectional and have distinct 5' and 3' ends.
DNA Replication Dynamics
- DNA polymerases can only add nucleotides to the 3' end of an existing strand.
- Complementarity of bases allows each DNA strand to serve as a template for its counterpart.
- Mismatches can be corrected by 3'-to-5' exonuclease activity of some DNA polymerases, though not all errors are eliminated.
Mutations and Environmental Factors
- Not all mutations are harmful; some can confer beneficial traits.
- DNA can incur damage from environmental agents like UV light and chemicals, contributing to mutation rates.
- Cells have evolved repair mechanisms, but they cannot address all damage from mutagens.
Bacterial vs. Eukaryotic DNA Replication
- Bacterial DNA replication initiates at a single origin, while eukaryotic replication occurs at multiple origins across chromosomes.
- Organisms that contain genes coding for telomerase are classified as eukaryotic.
Studying That Suits You
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Description
Test your understanding of DNA replication with these flashcards from Biology I, Chapter 14. Classify the roles of different components involved in the process and understand their functions. This quiz will help reinforce your knowledge of the essential enzymes and building blocks crucial for DNA synthesis.
