DNA Replication Models Flashcards
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Questions and Answers

Describe the dispersive model of DNA replication.

In the dispersive model, DNA replication results in two DNA molecules that are mixtures, or hybrids, of parental and daughter DNA. Each strand is a patchwork of original and new DNA.

Describe the conservative model of DNA replication.

In the conservative model, one DNA molecule consists of both original strands and another molecule consists of two new strands that have the same sequences as the original.

Describe the Semi-Conservative model of DNA replication.

In the Semi-Conservative model, the two strands of DNA unwind and each acts as a template for a new complementary strand, resulting in two DNA molecules, each containing one original strand and one new strand.

What test organism did Meselson and Stahl use in their centrifuge experiment?

<p>E. coli bacteria.</p> Signup and view all the answers

What did Meselson and Stahl experiment with?

<p>They grew E. coli in isotopes of Nitrogen, specifically 15N and 14N.</p> Signup and view all the answers

What is an isotope?

<p>An isotope is a version of an element that differs by the number of neutrons in its nucleus.</p> Signup and view all the answers

List the steps of the Meselson and Stahl centrifugation experiment.

<ol> <li>Grow E. coli in medium containing 15N. 2. Allow bacterial cells to grow. 3. Measure DNA density after switching to 14N medium.</li> </ol> Signup and view all the answers

Is 14N or 15N more dense?

<p>15N is more dense than 14N.</p> Signup and view all the answers

What happened when Meselson and Stahl allowed E. coli to grow on a medium containing 15N?

<p>The bacteria synthesized new biological molecules, including DNA, using heavy 15N.</p> Signup and view all the answers

How does the density gradient centrifugation method separate molecules?

<p>It separates molecules into bands by spinning them in a density gradient formed by cesium chloride.</p> Signup and view all the answers

What happens with ultra-centrifugation?

<p>A continuous density gradient is created.</p> Signup and view all the answers

How did the molecules band after centrifugation in Meselson and Stahl's experiment?

<p>The molecules banded at equal densities, creating a 14N/15N duplex medium density.</p> Signup and view all the answers

DNTPS is shorthand for what?

<p>Nucleotide triphosphates.</p> Signup and view all the answers

What is a nucleotide triphosphate?

<p>A highly reactive phosphate located on the 5' carbon.</p> Signup and view all the answers

What does the nucleotide triphosphate react with?

<p>The oxygen on the 3' carbon.</p> Signup and view all the answers

What is polymerization?

<p>Any process where small molecules combine to create a large chainlike or network molecule, called a polymer.</p> Signup and view all the answers

What is a polymerization reaction catalyzed by?

<p>The polymerase enzyme.</p> Signup and view all the answers

What is the function of a polymerization reaction?

<p>It creates the template that determines new strand order.</p> Signup and view all the answers

What direction does a polymerization reaction move in?

<p>It moves in a 5' to 3' direction.</p> Signup and view all the answers

Where do polymerization reactions get their energy from?

<p>Incoming dNTPS.</p> Signup and view all the answers

What is required for the initiation of a polymerization reaction?

<p>An RNA primer.</p> Signup and view all the answers

What direction does DNA polymerase III move in?

<p>5' to 3'.</p> Signup and view all the answers

DNA polymerase is template dependent.

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

List the initiator proteins in DNA replication.

<p>DnaA, DnaB, and DnaC.</p> Signup and view all the answers

Function of initiator protein.

<p>They attach to a specific origin sequence and cause local denaturation.</p> Signup and view all the answers

Types of primosomes.

<p>Helicase and primase.</p> Signup and view all the answers

How are primosomes formed?

<p>By DnaB and DnaC combining.</p> Signup and view all the answers

Function of helicase.

<p>It untwists the strands of DNA.</p> Signup and view all the answers

Function of primase.

<p>The RNA primer that provides a 3' OH.</p> Signup and view all the answers

What does SSBP stand for?

<p>Single strand binding proteins.</p> Signup and view all the answers

Function of a single strand binding protein.

<p>They bind to exposed template strands and prevent degradation and renaturation.</p> Signup and view all the answers

Function of gyrase.

<p>Reduces coiling ahead of the fork.</p> Signup and view all the answers

Study Notes

DNA Replication Models

  • Dispersive Model: Results in hybrid DNA molecules with patches of parental and daughter DNA interspersed; strands are mixtures of old and new.
  • Conservative Model: Produces one molecule that retains both original strands and one entirely new molecule; the parent duplex is conserved.
  • Semi-Conservative Model: Each strand unwinds and serves as a template for a new strand; results in two DNA molecules, each with one old strand and one new strand.

Meselson and Stahl Experiment

  • Test organism used: E. coli bacteria.
  • Experiment involved growing E. coli in two nitrogen isotopes: 15N (heavy) and 14N (light).
  • Isotope Definition: Different versions of an element based on neutron count.
  • Experiment method included density gradient centrifugation to separate DNA based on density from the isotopes.

Steps of the Experiment

  • E. coli cultured in 15N medium for several generations.
  • After labeling, bacteria switched to 14N medium for growth.
  • Samples collected across generations to assess DNA density changes.

Centrifugation Process

  • High-speed spinning with cesium chloride creates a density gradient.
  • Distinct bands formed after centrifugation based on DNA density; 15N more dense than 14N.
  • Resultant bands reflected 14N/15N duplex medium density.

DNA Structure and Reactions

  • dNTPs: Nucleotide triphosphates are highly reactive and essential for DNA synthesis.
  • Nucleotide triphosphates react at the 3' carbon with incoming nucleotides to facilitate polymerization.
  • Polymerization: Process where small molecules (monomers) combine to form large molecules (polymers), catalyzed by the polymerase enzyme.

Polymerization Characteristics

  • Direction of polymerization is from 5' to 3'.
  • Energy for reactions derives from incoming dNTPs.
  • Initiation of polymerization requires an RNA primer.

DNA Polymerase

  • DNA polymerase III: Functions in a 5' to 3' direction and is template-dependent.
  • Initiator Proteins: Include DnaA, DnaB, and DnaC; they attach to DNA at the origin and cause local denaturation.
  • Primosomes: Formed from helicase (DnaB) and primase (DnaC).
  • Helicase: Untwists DNA strands to allow for replication.
  • Primase: Synthesizes the RNA primer that provides a 3' hydroxyl (OH) for new strand synthesis.

Supporting Proteins and Enzymes

  • SSBPs (Single-Strand Binding Proteins): Bind to exposed single strands of DNA to prevent degradation and renaturation.
  • Gyrase: Reduces coiling ahead of the replication fork, easing the unwinding process.

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Description

Explore key concepts of DNA replication through this set of flashcards. Learn about different models such as the dispersive model and their implications in genetics. This quiz will help strengthen your understanding of how DNA replication occurs.

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