Nucleic Acids
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Questions and Answers

What is the primary function of DNA polymerase III during DNA replication?

  • It extends the 3’ end of the RNA primer. (correct)
  • It separates DNA strands at the replication fork.
  • It replaces RNA primers with DNA.
  • It synthesizes RNA primers.

Which statement correctly describes the synthesis of the lagging strand during DNA replication?

  • It involves the formation of Okazaki fragments. (correct)
  • It starts without any RNA primers.
  • It synthesizes continuously in the direction of the replication fork.
  • It only requires DNA polymerase I to function.

What is the role of primase in DNA replication?

  • It replaces RNA primers with DNA nucleotides.
  • It synthesizes DNA in the 3’ to 5’ direction.
  • It synthesizes RNA primers for DNA polymerase to extend. (correct)
  • It catalyzes the joining of Okazaki fragments.

Which enzyme is responsible for joining the Okazaki fragments on the lagging strand?

<p>DNA ligase (A)</p> Signup and view all the answers

How does DNA polymerase I function during DNA replication?

<p>It replaces RNA primers with DNA and fills in gaps. (C)</p> Signup and view all the answers

In the context of DNA replication, what does semi-conservative replication mean?

<p>Each new DNA molecule consists of one original strand and one newly synthesized strand. (A)</p> Signup and view all the answers

What accurately describes the structure of DNA?

<p>An antiparallel double helix with hydrogen bonds between bases. (D)</p> Signup and view all the answers

Which of the following correctly identifies the role of helicase in DNA replication?

<p>To unwind the double helix and separate the two strands. (B)</p> Signup and view all the answers

What is a key feature of the leading strand within the context of DNA replication?

<p>It is synthesized continuously in the direction of the fork. (D)</p> Signup and view all the answers

Which components are essential for the assembly of a new DNA strand during replication?

<p>DNA polymerase and deoxyribonucleotides. (D)</p> Signup and view all the answers

What type of reaction occurs to link the sugar and phosphate in the sugar-phosphate backbone of DNA?

<p>Dehydration reaction (D)</p> Signup and view all the answers

In the context of DNA, what does the term 'antiparallel' refer to?

<p>The directionality of the sugar-phosphate backbone (D)</p> Signup and view all the answers

What type of bonds hold the base pairs of DNA together?

<p>Hydrogen bonds (D)</p> Signup and view all the answers

During DNA replication, what is the role of the helicase enzyme?

<p>Separate DNA strands (B)</p> Signup and view all the answers

What characterizes the lagging strand during DNA replication?

<p>Synthesized in fragments (A)</p> Signup and view all the answers

Which component is essential for the initiation of DNA synthesis?

<p>RNA primer (C)</p> Signup and view all the answers

What model describes how daughter DNA strands are formed during replication?

<p>Semiconservative model (C)</p> Signup and view all the answers

Which of the following statements about DNA replication is true?

<p>Replication occurs at multiple origins in human cells (C)</p> Signup and view all the answers

What was the main conclusion of the Avery experiment in 1944?

<p>DNA is essential for the transformation of R cells to pathogenic S cells. (D)</p> Signup and view all the answers

How are base pairs arranged within the structure of DNA?

<p>Purines pair with pyrimidines (B)</p> Signup and view all the answers

What role do topoisomerases play in DNA replication?

<p>Relieve tension in the DNA strand ahead of the replication fork (C)</p> Signup and view all the answers

In the Hershey and Chase experiment, what was specifically labeled to identify the genetic material?

<p>DNA of the bacteriophage (C)</p> Signup and view all the answers

What are the two types of nitrogenous bases in DNA?

<p>Purines and pyrimidines (C)</p> Signup and view all the answers

Which of the following best describes the structure of DNA?

<p>Double helix with antiparallel strands and a sugar-phosphate backbone (B)</p> Signup and view all the answers

What did the Griffith experiment demonstrate regarding R and S cells?

<p>A chemical from heat-killed S cells can transform R cells to be pathogenic. (D)</p> Signup and view all the answers

Which statement accurately reflects Chargaff's rules?

<p>Adenine is found in equal amounts to thymine, and cytosine is equal to guanine. (D)</p> Signup and view all the answers

What role did X-ray diffraction play in the discovery of DNA structure?

<p>It provided crucial data that supported the helical structure of DNA. (A)</p> Signup and view all the answers

What are the components of a nucleotide in DNA?

<p>Phosphate, sugar, and nitrogenous base (D)</p> Signup and view all the answers

What was the important finding of the label with 35S and 32P in the Hershey and Chase experiment?

<p>Viral DNA, but not viral protein, entered the bacterial cells. (C)</p> Signup and view all the answers

Why are adenine and thymine considered complementary bases in DNA?

<p>They pair together through hydrogen bonds. (D)</p> Signup and view all the answers

Flashcards

Griffith experiment

An experiment demonstrating that a chemical from heat-killed bacteria could transform harmless bacteria into pathogenic ones.

Avery experiment

An experiment identifying DNA as the transforming principle in heat-killed bacteria.

Hershey-Chase experiment

An experiment showing that DNA, not protein, is the genetic material of viruses.

Bacteriophage (phage)

A virus that infects bacteria.

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DNA

Deoxyribonucleic acid; the molecule that carries genetic information.

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Nucleotide monomers

The building blocks of DNA, each including a phosphate, sugar, and nitrogenous base.

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Purines

A type of nitrogenous base with a double-ring structure; Adenine and Guanine.

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Pyrimidines

A type of nitrogenous base with a single-ring structure; Cytosine and Thymine.

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Double helix

The 3D structure of DNA, a twisted ladder-like shape.

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Antiparallel strands

DNA's two strands running in opposite directions.

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Sugar-phosphate backbone

The structural backbone of DNA, formed by alternating sugar and phosphate molecules.

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DNA replication

Process of creating a copy of DNA to ensure each cell division gets a copy

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Semiconservative model

Each new DNA molecule contains one original strand and one newly synthesized strand.

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Replication fork

The point where the DNA double helix separates during replication.

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Helicase enzyme

Enzyme that unwinds the DNA double helix to separate DNA strands during replication.

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Leading strand

New strand synthesized continuously in the 5' to 3' direction during DNA replication.

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Lagging strand

New strand synthesized in short fragments (Okazaki fragments) during DNA replication.

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Okazaki fragments

Short fragments of DNA synthesized on the lagging strand during DNA replication.

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DNA polymerase

Enzyme responsible for building new DNA strands.

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DNA polymerase III

An enzyme responsible for the synthesis of new DNA strands during replication. It adds nucleotides to the 3' end of a growing DNA strand, working in a 5' to 3' direction.

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RNA primer

A short segment of RNA that provides a starting point for DNA polymerase III to begin synthesizing a new DNA strand.

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Continuous synthesis

The process of DNA replication on the leading strand, where DNA polymerase III adds nucleotides continuously in the direction of the replication fork.

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Primase

An enzyme that synthesizes short RNA primers, providing starting points for DNA polymerase III.

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DNA ligase

An enzyme that joins the Okazaki fragments together, creating a continuous DNA strand on the lagging strand.

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Helicase

An enzyme that unwinds the DNA double helix, separating the two strands to create a replication fork.

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Study Notes

Nucleic Acids and Inheritance

  • The lecture discusses DNA as the genetic material.
  • Griffith's experiment (1928) used Streptococcus bacteria to demonstrate transformation. Living S cells (pathogenic) killed mice, whereas living R cells (nonpathogenic) did not. Heat-killed S cells also did not kill mice, but a mixture of heat-killed S cells and living R cells killed mice. This suggested a chemical, called the "transforming principle," from heat-killed S cells could transform R cells to pathogenic cells.
  • Avery's experiment (1944) identified DNA as the transforming principle. Avery, MacLeod, and McCarty demonstrated that DNA from heat-killed S cells was required for transforming R cells, while RNA and protein did not work. This confirmed DNA's role as the genetic material.
  • Hershey and Chase's experiment (1952) further supported DNA as the genetic material. The experiment used bacteriophages (viruses that infect bacteria). The bacteriophages were labeled with either radioactive phosphorus (32P) or radioactive sulfur (35S). The results showed that labeled phage DNA entered the bacterial cells, but labeled phage protein did not. These results strongly supported DNA as the genetic material.

DNA Structural Properties

  • DNA is a double helix.
  • The structure is composed of nucleotide monomers. Each nucleotide has a phosphate group, a sugar (deoxyribose), and a nitrogenous base.
  • Nitrogenous bases are categorized as purines (adenine and guanine) and pyrimidines (cytosine and thymine). Purines are double-ringed, and pyrimidines are single-ringed.
  • DNA strands are antiparallel.
  • The sugar-phosphate backbone forms the outer structure of the helix.
  • Nitrogenous bases are paired in the center of the helix via hydrogen bonds.
  • Adenine pairs with Thymine (A-T)
  • Guanine pairs with Cytosine (G-C).
  • Base pairs have the same width, which is crucial for the consistent structure of the DNA double helix. Adenine and Guanine pair with the corresponding base, Thymine and Cytosine in the opposite strand.

Replication

  • DNA replication is the process of copying DNA.
  • It is semiconservative, meaning each new DNA molecule contains one original and one newly synthesized strand.
  • Replication starts at specific origins of replication.
  • New strands are synthesized in the 5' to 3' direction.
  • Leading strand replication is continuous; lagging strand replication is discontinuous, creating Okazaki fragments.
  • DNA polymerase III synthesizes new DNA strands, and DNA polymerase I removes RNA primers.
  • DNA ligase joins the Okazaki fragments.
  • Replication proceeds bidirectionally from the origin of replication.
  • Typical bacteria have one origin of replication, while human cells have multiple.

Replication Enzyme Toolbox

  • Helicase: Separates the DNA strands at the replication fork.
  • Single-strand binding proteins (SSBs): Stabilize the separated DNA strands.
  • Topoisomerase: Relieves the strain on the DNA ahead of the replication fork by breaking, swiveling, and rejoining DNA strands.
  • Primase: Synthesizes short RNA primers, which provide a starting point for DNA polymerase to add nucleotides.
  • DNA polymerase III: Synthesizes new DNA strands, following the 5' to 3' direction, and is primarily responsible for the leading strand, also creating Okazaki fragments which make up the lagging strand.
  • DNA polymerase I: Removes RNA primers and replaces them with DNA nucleotides.
  • DNA ligase: Joins Okazaki fragments together on the lagging strand to create a continuous DNA strand.

Additional Information from the Lecture:

  • The lecture emphasizes that DNA is the genetic material, building on seminal experiments to justify this central role.

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