Introduction to Viruses and Genetics

• Measles caused by a contagious virus, identifiable by a red rash.

• The virus was almost eradicated in the U.S. until a 2014 outbreak.

• Understanding of DNA and RNA is crucial in combating viruses.

Big Ideas in Molecular Biology

• The Structure of Genetic Material

• DNA Replication

• Flow of Genetic Information: DNA → RNA → Protein

• Genetics of Viruses and Bacteria

The Structure of Genetic Material

Experiments Demonstrating DNA as Genetic Material

• Early 20th century: The basis for inheritance was unclear.

• Frederick Griffith's Experiment (1928):

  • Mixed dead pathogenic bacteria with live harmless bacteria.

  • Result: Some harmless bacteria became pathogenic, inheriting this trait.

• Hershey and Chase Experiment:

  • Used phages (bacterial viruses) to show DNA, not protein, is the genetic material.

  • Phage DNA directed the host cell to produce more phages.

DNA and RNA Polymers

• Nucleic Acids (DNA/RNA): Long chains of nucleotides.

• Nucleotide Structure:

  • Nitrogenous base, five-carbon sugar, phosphate group.

• DNA vs RNA:

  • DNA: Uses deoxyribose, bases include A, C, T, G.

  • RNA: Uses ribose, base uracil (U) instead of thymine (T).

The Double Helix Structure of DNA

• Watson and Crick discovered DNA is a double-stranded helix.

• Base pairing:

  • A with T

  • G with C

• The structure allows for the storage and replication of genetic information.

• Nobel Prize awarded in 1962 to Watson, Crick, and Wilkins.

• Rosalind Franklin's contributions are acknowledged posthumously.

DNA Replication

Process of DNA Replication

• Begins with separation of DNA strands.

• Enzymes create complementary strands using each original strand as a template.

• Semiconservative Model:

  • Each new helix has one old strand and one new strand.

Visual Representation of DNA Replication

• Parental DNA molecules serve as templates for new daughter strands.

• Results in two identical DNA molecules.

Flow of Genetic Information

From DNA to Protein

• Genes (sequences of DNA) are transcribed into RNA, then translated into proteins.

• Transcription: DNA → RNA synthesis.

• Translation: RNA → Proteins synthesis.

Codons and Genetic Code

• Codons: Triplet code that corresponds to amino acids.

• The same genetic code is used across nearly all organisms.

Mutations and Their Effects

• Mutations: Changes in genetic information due to DNA replication errors or environmental factors.

• Effects vary based on nucleotides substituted, inserted, or deleted.

Genetics of Viruses and Bacteria

Viruses

• Viral Structure:

  • Consist of nucleic acids (DNA/RNA) encased in a protein coat (capsid).

• Lytic Cycle: Virus replicates its DNA, assembles new virions, bursts host cell.

• Lysogenic Cycle: Viral DNA integrates into host chromosome, replicates with host cell's DNA, remains dormant.

Emerging Viruses

• Emerging viruses can quickly become significant health threats (e.g., HIV, Coronavirus).

• Understanding of genetic principles critical for response.

Summary of Key Experiments

• Griffith, Hershey, and Chase's experiments all support that DNA is the genetic material.

• Structural differences between DNA and RNA are crucial for understanding their functions.

• The DNA structure enables effective replication essential for heredity.