DNA Replication Quiz

Chapter 16: The Molecular Basis of Inheritance

• Learning Objectives:
  • Understand how DNA is the genetic material of cells/organisms.
  • Know the structural details of DNA.
  • Understand the process of DNA replication, including the enzymes and proteins involved.
  • Know the levels of chromosome structure.

Concept 16.1: DNA is the Genetic Material- How Do We Know?

• Early 20th century, identifying inheritance molecules was a challenge for biologists.
• DNA's role in heredity was first discovered by studying bacteria and viruses that infect them.

Evidence That DNA Can Transform Bacteria

• In 1928, Frederick Griffith discovered bacterial transformation.
• Griffith experimented with two bacterial strains: pathogenic (harmful) and harmless.
• Mixing heat-killed pathogenic bacteria with harmless bacteria caused some of the harmless bacteria to become pathogenic.
• This indicated a transfer of genetic material.

Evidence That DNA Can Transform Bacteria

• Oswald Avery, Maclyn McCarty, and Colin MacLeod identified DNA as the transforming substance.
• Their work showed that DNA from pathogenic bacteria could transfer genetic traits to harmless bacteria, confirming DNA's role in heredity.
• Many biologists were skeptical at first, mostly due to the limited knowledge about DNA.

Evidence That Viral DNA Can Program Cells

• More evidence from studies of viruses that infect bacteria (bacteriophages or phages).
• Viruses are DNA (or sometimes RNA) enclosed in a protein coat.
• Phages are widely used in molecular genetics research.

Evidence That Viral DNA Can Program Cells

• In 1952, Alfred Hershey and Martha Chase demonstrated that DNA, not protein, is the genetic material of a phage (bacteriophage T2).

• They designed an experiment using bacteriophages, labeling either the protein coat or the DNA with radioactive isotopes.

• Their findings proved that only the DNA entered the bacterial cell, thus transferring the genetic information.

Concept 16.2: Structure of DNA

• DNA is composed of four nucleotide pairs (A+T, C+G).
• Phosphodiester bonds link nucleotides in a single strand.
• DNA strands have polarity (5' and 3' ends).
• Antiparallel DNA strands bond together with hydrogen bonds.

DNA vs. RNA: Key Differences

Figure 16.9 Base Pairing in DNA

• Purines (A & G) have double C-N rings.
• Pyrimidines (C, T, & U) have single C-N rings.
• Bases pair specifically (A with T, and C with G).

Building a Structural Model of DNA

• X-ray crystallography, using X-ray diffraction, was crucial for understanding DNA structure.
• Rosalind Franklin's X-ray diffraction images of DNA provided crucial data that enabled James Watson.
• Watson and Crick then deduced that DNA is a double helix.

Where are they now?

• Rosalind Franklin died of cancer from X-ray exposure in 1958.
• Watson, Wilkins, and Crick were awarded the Nobel Prize in 1962.
• Wilkins, and Crick died during 2000s.

Reviewing DNA Strx-Group Activity

• Group A: Nucleotide components, nitrogenous bases, differences between deoxyribose and ribose sugar, and DNA vs. RNA differences.
• Group B: DNA strand backbone molecules, phosphodiester linkages, antiparallel strands, bonds holding base pairs.

Concept 16.2: DNA Replication and Repair

• DNA replication is crucial for inheritance, ensuring faithful transmission of genetic information in cell division.
• DNA replication occurs before mitosis.
• Specific base pairing supports a possible copying mechanism.
• DNA replication is the process of copying DNA.

Figure 16.1b How Does DNA Replication Transmit Genetic Information?

• DNA replication is the process of transmitting genetic information from parent to daughter cells during mitosis (and meiosis).
• Replication begins at specific sites (origins of replication).
• Replication proceeds in both directions from each site along the DNA.

The Basic Principle: Base Pairing to a Template Strand

• Each DNA strand acts as a template during replication.
• DNA replication is semiconservative.

DNA Replication: The Mechanism

• DNA replication is rapid and accurate.
• Many enzymes and proteins are involved.
• Bacterial replication is better understood.

Getting Started

• Replication begins at origin(s) of replication, creating a replication bubble.
• Chromosomes (eukaryotic) may have many origins of replication.
• Replication progresses in both directions from each origin.

Replication Initiation

• Several proteins initiate replication.
• Helicases untwist the double helix at replication forks, separating the strands.
• Single-strand binding proteins stabilize single-stranded DNA.
• Topoisomerase relieves the strain ahead of the replication forks.

Synthesizing a New DNA Strand

• DNA polymerases synthesize new DNA strands.
• DNA polymerases require a primer.
• A short RNA primer is synthesized by primase.

Antiparallel Elongation

• DNA polymerase only adds nucleotides to the free 3' end of a growing strand.
• Leading strand is synthesized continuously.
• Lagging strand is synthesized discontinuously in Okazaki fragments.

Proofreading and Repairing DNA

• DNA polymerase can proofread and repair errors.
• Nucleotide excision repair removes and replaces damaged stretches of DNA.

Evolutionary Significance of Altered DNA Nucleotides

• Errors occur during DNA replication, but are usually corrected.
• Sequence changes (mutations) are the source of genetic variation responsible for the appearance of new species.
• Random mutations are the reason for evolution.

Replicating the Ends of DNA Molecules

• Linear DNA ends (telomeres) cannot be fully replicated by DNA polymerase.
• Telomeres shorten during each replication cycle.
• Telomerase, an enzyme, lengthens telomeres.

Concept 16.3: Chromosome Structure

• DNA is packaged into chromatin in eukaryotic cells.
• Histones, proteins, are essential for DNA packing.
• Chromatin undergoes different levels of condensation (organization) throughout the cell cycle.
• Euchromatin and heterochromatin differ in their condensation levels.

Environmental Factors

• Environmental factors like famine, toxins, or extreme stress can cause epigenetic changes that can be passed to future generations.
• Intergenerational trauma may cause epigenetic changes impacting mental health.
• Maternal nutrition during pregnancy may affect the epigenetic profile of the fetus, influencing later health.

Test your knowledge on the crucial processes involved in DNA replication. This quiz covers various enzymes, functions, and historical experiments that highlighted the role of DNA as genetic material. Dive into the specifics of each component involved in this essential biological process.