Biology 1.2
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Questions and Answers

What is the primary role of primers in PCR?

  • To separate DNA strands at high temperatures
  • To serve as starting points for DNA synthesis (correct)
  • To provide energy for DNA synthesis
  • To unwind the DNA double helix

Which factor is essential for successful DNA amplification using PCR?

  • Electrophoresis equipment
  • Availability of RNA primers
  • A stable DNA template (correct)
  • Presence of reverse transcriptase

Why are short DNA fragments generated during the lagging strand synthesis during replication?

  • Lagging strands do not require additional enzymes
  • The antiparallel structure dictates the synthesis direction (correct)
  • Polymerase can only work in the 3' to 5' direction
  • Nucleotides are added predominantly to the 5' end

What is the primary purpose of using primers in the Polymerase Chain Reaction (PCR)?

<p>To provide starting points for DNA synthesis (C)</p> Signup and view all the answers

Which of the following is NOT a practical application of PCR?

<p>Reversing mutations in DNA sequences (C)</p> Signup and view all the answers

In PCR, how are primers specifically chosen for a particular target sequence?

<p>By matching them to unique sequences surrounding the target DNA (C)</p> Signup and view all the answers

What role does heat-tolerant DNA polymerase play in PCR?

<p>It adds nucleotides to the growing DNA strand during amplification (A)</p> Signup and view all the answers

Which statement best describes the role of primers in DNA replication during PCR?

<p>They initiate DNA synthesis by providing a free 3' hydroxyl group (D)</p> Signup and view all the answers

How can PCR be used in forensic science?

<p>To amplify minute quantities of DNA from crime scenes (B)</p> Signup and view all the answers

Which of the following best describes thermal cycling in PCR?

<p>Repeated heating and cooling to denature DNA and enable replication (D)</p> Signup and view all the answers

Which property of heat-tolerant DNA polymerase is particularly beneficial for PCR?

<p>Its resilience to high temperatures without denaturing (A)</p> Signup and view all the answers

What is the role of primers in the Polymerase Chain Reaction (PCR)?

<p>To provide a starting point for DNA polymerase to replicate DNA (D)</p> Signup and view all the answers

Which statement best describes the significance of using two primers in PCR?

<p>They target opposing strands for replication (C)</p> Signup and view all the answers

What must occur prior to the binding of primers during the PCR process?

<p>The DNA must be heated to break hydrogen bonds (A)</p> Signup and view all the answers

What is the expected outcome after one complete cycle of PCR?

<p>Two identical copies of DNA (C)</p> Signup and view all the answers

Which of the following best describes how PCR can be applied in forensics?

<p>It amplifies trace amounts of DNA for analysis (C)</p> Signup and view all the answers

Why is heat-tolerant DNA polymerase crucial in PCR?

<p>It prevents denaturation during the heating cycle (C)</p> Signup and view all the answers

What is the main purpose of heating the DNA to temperatures between 92-98°C at the start of the PCR cycle?

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

Flashcards

Lagging Strand Replication

DNA replication occurs in fragments on the 3' to 5' template strand, requiring primers at each fragment start point, and ligase to join the fragments.

Polymerase Chain Reaction (PCR)

A lab technique that quickly copies specific DNA sequences.

PCR Primers

Short DNA sequences that bind to specific DNA targets and initiate replication.

PCR Requirements

DNA template, primers, nucleotides (building blocks), and heat-resistant DNA polymerase.

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PCR Thermal Cycling

Repeating cycles of heating and cooling DNA to separate strands, allow primer binding, and enable DNA replication.

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DNA Denaturation (PCR)

High heat separates the DNA double helix into single strands.

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Primer Binding (PCR)

Primers attach to complementary sequences on single-stranded DNA.

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DNA Replication (PCR)

Heat-tolerant DNA polymerase adds nucleotides to the primers, extending the new DNA strands.

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DNA Replication's Importance

DNA replication creates exact copies of DNA before cell division, ensuring daughter cells inherit identical genetic information.

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DNA Replication Requirements

DNA replication needs a DNA template, free nucleotides, primers, DNA polymerase, and ligase.

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DNA Replication Stages

DNA replication involves unwinding the double helix, separating the strands, using each strand as a template to build a new complementary strand, and finally joining the new strands to create two identical DNA molecules.

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What is a primer?

A primer is a short sequence of DNA nucleotides that binds to a template strand to initiate DNA replication.

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DNA Polymerase

DNA polymerase is an enzyme that adds free nucleotides to a growing DNA strand during replication.

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Ligase

Ligase is an enzyme that joins DNA fragments together to create a complete DNA strand.

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Direction of DNA Replication

DNA replication always proceeds in the 5' to 3' direction on the new strand, meaning nucleotides are added to the free 3' hydroxyl group.

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PCR Purpose

PCR is a technique used to amplify specific DNA sequences, making many copies of a target DNA region.

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DNA Replication - Lagging Strand

The lagging strand of DNA is synthesized discontinuously in short fragments called Okazaki fragments, due to the antiparallel nature of DNA and the 5' to 3' directionality of DNA polymerase.

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What is required for DNA replication?

DNA replication requires a template DNA strand, DNA polymerase, nucleotides, primers, and ATP (energy).

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Why is DNA replication necessary?

DNA replication is essential for cell division and growth to ensure that each new cell receives a complete copy of the genetic material.

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PCR (Polymerase Chain Reaction)

PCR is a laboratory technique used to rapidly amplify specific DNA sequences, creating millions of copies from a small sample.

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Taq Polymerase in PCR

Taq polymerase is a heat-resistant enzyme used in PCR to withstand the high temperatures required for DNA denaturation, allowing efficient DNA replication.

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Pfu Polymerase in PCR

Pfu polymerase is another heat-resistant enzyme used in PCR with 'proofreading' activity; it checks for errors during replication and corrects them, resulting in higher fidelity amplification.

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PCR Cycle Time

Each cycle of PCR takes approximately 5 minutes and involves denaturation (heating), annealing (primers binding), and extension (copying) steps.

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Number of DNA Fragments in PCR

Each PCR cycle doubles the number of DNA fragments. To calculate the time to reach a specific number of fragments, consider the doubling effect of each cycle.

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Study Notes

DNA Replication

  • DNA replication is essential before cell division to ensure each daughter cell receives an identical copy of the genetic material.
  • Five essential components for DNA replication are: DNA template, primers, free DNA nucleotides, enzymes, and ATP.

Stages of DNA Replication

  • The DNA unwinds, and hydrogen bonds between base pairs break, forming two template strands.
  • Nucleotides align with their complementary bases on the template strand to form new base pairs (hydrogen bonds form).
  • New sugar-phosphate backbones are formed on the new strands.
  • The final product is two identical DNA molecules, identical to the original parent DNA.

Primers in DNA Replication

  • Primers are short strands of nucleotides that initiate DNA replication.
  • They are crucial because DNA polymerase can only add nucleotides to an existing chain, and primers provide this starting point.

DNA Replication Enzymes

  • DNA polymerase is an enzyme that adds new nucleotides in the 5' to 3' direction to the leading strand continuously.
  • DNA polymerase has to add nucleotides in fragments to the lagging strand.
  • Ligase joins the Okazaki fragments, completing the lagging strand.
  • These are involved in DNA replication.

Direction of Replication

  • DNA replication is always in the 5' to 3' direction.
  • The leading strand is built continuously in the 5' to 3' direction along, which is the direction of replication. This is due to DNA Polymerase working in this direction.
  • The lagging strand is built discontinuously in short fragments (Okazaki fragments) in the opposite direction.

Polymerase Chain Reaction (PCR)

  • PCR is a technique used to amplify DNA in a laboratory.
  • A single DNA strand can be duplicated into millions, allowing for analysis.
  • The purpose is to make multiple copies of a specific DNA sequence.
  • The process involves a series of temperature changes to allow for DNA strand separation (denaturation), primer annealing, and DNA synthesis (extension).
  • Heat-tolerant DNA polymerase is crucial because it can withstand the high temperatures needed for DNA denaturation.
  • Primers are specific sequences that bind to the target DNA to be replicated.
  • Thermal cycling involves repeatedly heating and cooling the DNA to complete each PCR replication cycle.

PCR Applications

  • PCR is used to amplify small amounts of DNA from a variety of sources, such as crime scenes, blood, or tissue samples.
  • It is used in genetic testing and diagnostics, such as prenatal genetic testing or paternity testing.

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