Biology I - Chapter 14 DNA Replication
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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?

<p>phosphate-sugar-base</p> Signup and view all the answers

Why do complementary nucleotides across the double-stranded DNA bond together using hydrogen bonds rather than covalent bonds?

<p>Covalent bonds would be too strong to allow the double helix to easily separate and make templates available for replication and transcription.</p> Signup and view all the answers

According to Chargaff's rule, A = T and C = G and A + G = C + T.

<p>True</p> Signup and view all the answers

Why is the replication machinery found at the replication fork?

<p>The replication machinery must have access to the leading and lagging strands for replication, and it must be able to open and stabilize the template DNA.</p> Signup and view all the answers

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?

<p>Because the structure of both G and A are similar in that they have a double ring.</p> Signup and view all the answers

Which of the following synthesizes the daughter strands during DNA replication?

<p>DNA polymerase</p> Signup and view all the answers

Why is the lagging strand synthesized in a discontinuous fashion?

<p>DNA synthesis must occur in a 5' to 3' direction, which imposes spatial constraints on the synthesis of the lagging strand.</p> Signup and view all the answers

Arrange the following proteins in the proper order in which they participate in DNA replication:

<p>Primase = 1 Helicase = 2 Single-strand binding proteins = 3 DNA polymerase I = 4</p> Signup and view all the answers

What is required to replicate the lagging strand of DNA?

<p>Okazaki fragments, primase, and DNA ligase</p> Signup and view all the answers

RNA primers are removed by the action of which enzyme?

<p>DNA Pol I</p> Signup and view all the answers

If DNA polymerase III could add nucleotides in either direction, Okazaki fragments would no longer form.

<p>True</p> Signup and view all the answers

The enzyme that unwinds a segment of the DNA molecule is?

<p>helicase</p> Signup and view all the answers

How do DNA polymerase I and DNA polymerase III differ?

<p>DNA Polymerase III synthesizes the majority of the DNA, while DNA Polymerase I synthesizes DNA in the regions where the RNA primers were laid down on the lagging strand.</p> Signup and view all the answers

What is unique about telomerase?

<p>It contains an RNA molecule</p> Signup and view all the answers

Which of the following best describes the function of telomerase at the telomere?

<p>It adds new DNA to the longer strand of the telomere overhang.</p> Signup and view all the answers

Based on his experiments with the bacterium S. pneumoniae, what conclusion did Griffith reach?

<p>He concluded that the genetic information for virulence was transferred from dead, virulent cells to live, nonvirulent cells, a process he called transformation.</p> Signup and view all the answers

What did Avery, MacLeod, and McCarty determine as the substance responsible for converting live, nonvirulent bacteria into live, virulent bacteria?

<p>DNA</p> Signup and view all the answers

What did Hershey and Chase use to demonstrate that DNA is the genetic material of phages?

<p>Radioactively labeled protein and DNA</p> Signup and view all the answers

Because the 2 strands of a DNA molecule run in opposites, they are said to be bidirectional.

<p>False</p> Signup and view all the answers

DNA polymerases can add new DNA nucleotides only to the 5' end of an existing strand.

<p>False</p> Signup and view all the answers

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.

<p>True</p> Signup and view all the answers

The DNA strand that grows away from the replication fork is synthesized continuously from one initial primer.

<p>False</p> Signup and view all the answers

The DNA strand that grows toward the replication fork is synthesized discontinuously in short pieces called Okazaki fragments.

<p>False</p> Signup and view all the answers

Each Okazaki fragment has its own primer.

<p>True</p> Signup and view all the answers

The DNA strand that is synthesized continuously is called the lagging strand.

<p>False</p> Signup and view all the answers

The DNA strand that is synthesized discontinuously is called the leading strand.

<p>False</p> Signup and view all the answers

DNA ligase joins adjacent Okazaki fragments together into a complete strand.

<p>True</p> Signup and view all the answers

DNA polymerases cannot initiate synthesis of a new DNA strand; they can only add bases to an existing strand.

<p>True</p> Signup and view all the answers

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?

<p>complementarity of the bases</p> Signup and view all the answers

Many DNA polymerases have 3'-to-5' exonuclease activity that allows 'proofreading' and replacement of incorrect bases.

<p>True</p> Signup and view all the answers

Proofreading effectively eliminates all errors during DNA replication.

<p>False</p> Signup and view all the answers

Although most mutations are harmful, some may be beneficial.

<p>True</p> Signup and view all the answers

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.

<p>False</p> Signup and view all the answers

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.

<p>True</p> Signup and view all the answers

Agents that damage DNA can lead to mutations.

<p>True</p> Signup and view all the answers

Any agent that decreases the number of mutations below background levels is called a mutagen.

<p>False</p> Signup and view all the answers

Cells cannot escape exposure to mutagens, but they have evolved systems that enable them to repair all of the damage.

<p>False</p> Signup and view all the answers

When does DNA replication in bacteria begin?

<p>at a single origin and proceeds in both directions.</p> Signup and view all the answers

How is bacterial DNA replication different from eukaryotic DNA replication?

<p>Bacterial DNA replication begins at a single location on the chromosome, while eukaryotic DNA replication begins in many places throughout each chromosome.</p> Signup and view all the answers

What can be concluded about an organism if genetic analysis indicates it contains the gene that codes for telomerase?

<p>It is eukaryotic.</p> Signup and view all the answers

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.

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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.

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