DNA Replication Overview and Steps

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Questions and Answers

Match the following scientists with their primary discoveries related to DNA.

Griffith = Demonstrated that genetic material could be transferred between bacteria through transformation. Avery, McCarty, and MacLeod = Identified DNA as the transforming principle, disproving the protein hypothesis. Hershey and Chase = Confirmed DNA as the genetic material using bacteriophages and radioactive labeling. Wilkins and Franklin = Used X-ray diffraction to deduce DNA's helical structure. Watson and Crick = Proposed the double helix model of DNA, incorporating Chargaff's rules and base pairing.

Which of the following describes the process by which DNA replicates?

  • Conservative replication: The original DNA molecule remains intact, and a completely new copy is created.
  • Dispersive replication: The original DNA molecule is broken into fragments, and each fragment is replicated, resulting in a mixture of old and new DNA in the daughter molecules.
  • Semiconservative replication: Each daughter DNA molecule contains one original strand and one newly synthesized strand. (correct)

What are the four nitrogenous bases found in DNA?

Adenine, guanine, cytosine, and thymine.

Which of these is NOT a component of a nucleotide?

<p>Amino acid (A)</p> Signup and view all the answers

DNA polymerase can synthesize a new DNA strand in both the 5' to 3' and the 3' to 5' directions.

<p>False (B)</p> Signup and view all the answers

What is the main function of DNA polymerase III in DNA replication?

<p>Adding nucleotides to the new DNA strand (A)</p> Signup and view all the answers

Which enzyme is responsible for creating RNA primers during DNA replication?

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

What are the short, newly synthesized DNA fragments on the lagging strand called?

<p>Okazaki fragments (D)</p> Signup and view all the answers

The enzyme ______ removes torsional strain that builds up ahead of the replication fork during DNA unwinding.

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

What is the purpose of telomeres?

<p>They protect the ends of chromosomes from degradation and prevent the loss of genetic information during DNA replication.</p> Signup and view all the answers

Which of the following is TRUE regarding Hayflick's Limit?

<p>It refers to the maximum number of times a normal human cell can divide before senescence. (D)</p> Signup and view all the answers

Which of the following enzymes is NOT directly involved in DNA replication?

<p>RNA polymerase (D)</p> Signup and view all the answers

Which of these is a key characteristic of DNA replication?

<p>It is bidirectional, proceeding in both directions from the origin of replication. (A)</p> Signup and view all the answers

The lagging strand is synthesized continuously in the 5′ to 3′ direction.

<p>False (B)</p> Signup and view all the answers

What is the function of DNA ligase in DNA replication?

<p>DNA ligase seals the gaps between the newly synthesized Okazaki fragments on the lagging strand, creating a continuous DNA molecule.</p> Signup and view all the answers

Flashcards

Griffith experiment

Demonstrated that genetic material could be transferred between bacteria.

Avery, MacLeod, McCarty experiment

Determined that DNA is the transforming principle.

Hershey-Chase experiment

Confirmed DNA is the genetic material of viruses.

The transforming principle

The material responsible for genetic transformation in bacteria.

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DNA

Deoxyribonucleic acid, the genetic material in most organisms.

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Nucleotide

The monomer unit of DNA and RNA; composed of a sugar, phosphate, and base.

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Base Pairing

Specific hydrogen bonding between nitrogenous bases in DNA (A-T, G-C).

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Chargaff's rule

DNA has equal amounts of A and T, and equal amounts of G and C.

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Double helix

The twisted-ladder structure of DNA.

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3' and 5' ends

The ends of a DNA strand, specifying the direction of synthesis.

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Semiconservative replication

Each new DNA molecule has one old strand and one new strand.

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DNA polymerase III

Adds nucleotides to a DNA strand during replication.

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Helicase

Enzyme that unwinds the DNA double helix.

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Primase

Enzyme that creates RNA primers for DNA replication.

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Okazaki fragments

Short DNA fragments synthesized on the lagging strand during replication.

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DNA ligase

Connects Okazaki fragments during DNA replication.

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Topoisomerase

Reduces tension in DNA during replication.

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Telomeres

Repeated sequences at the ends of DNA chromosomes.

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Telomerase

Extends telomeres to prevent shortening during replication.

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DNA Replication origin (ori)

The site where DNA replication begins.

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Leading strand

The DNA strand that is synthesized continuously during DNA replication.

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Lagging strand

The DNA strand that is synthesized discontinuously during DNA replication.

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Proofreading

The DNA polymerase's ability to correct errors during DNA replication.

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DNA repair mechanisms

Complex systems that scan newly synthesized DNA for and fix mistakes missed by proofreading.

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Study Notes

DNA Replication - Overview

  • DNA replication is the process of creating two identical DNA molecules from one original DNA molecule.
  • This process crucial for cell division and heredity.

DNA Replication - Steps

  • DNA replication begins at specific sites called origins of replication.
  • The double helix unwinds and unzips.
  • Each strand serves as a template for a new strand.
  • Nucleotides are added according to complementary base pairing (A with T, and G with C).
  • DNA polymerase adds nucleotides to the 3' end of the new strand, always in the 5' to 3' direction.
  • The leading strand is synthesized continuously in the 5' to 3' direction.
  • The lagging strand is synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction.
  • Okazaki fragments are joined together by DNA ligase.

Replication Components/Enzymes

  • Helicase: unwinds the DNA double helix
  • Topoisomerase (gyrase): relieves strain in the DNA molecule ahead of the replication fork.
  • Single-stranded binding proteins (SSBs): stabilize the single-stranded DNA during replication.
  • Primase: synthesizes RNA primers.
  • DNA polymerase III: adds nucleotides to the 3' end of the growing DNA strand.
  • DNA polymerase I: removes RNA primers and replaces them with DNA.
  • DNA ligase: joins Okazaki fragments.

DNA Replication Errors

  • Errors during DNA replication can occur, but are typically corrected by mechanisms such as proofreading.
  • Proofreading: DNA Polymerase III can identify and correct errors to ensure accurate DNA replication (errors ~1 in 1,000,000).
  • DNA repair mechanisms: specialized proteins that scan the newly synthesized DNA and repair any missed errors by DNA Polymerase III.

Telomeres

  • Telomeres are repetitive sequences of DNA located at the ends of linear chromosomes.
  • Telomeres protect the chromosomes from degradation and fusion.
  • Telomeres shorten during each round of replication, leading to cellular senescence.
  • Telomerase is an enzyme that can extend telomeres, preventing their shortening. This is present in germ cells, stem cells but not most somatic cells which undergo mitosis without telomerase.

DNA Packaging

  • DNA is packaged into chromosomes as chromatin.
  • Nucleosomes form by wrapping DNA around histone proteins.

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