Molecular Cell Biology - Lecture 4 Study Questions

Discoveries of DNA as Genetic Material:

• Griffith experiment (1928)

• Avery-MacLeod-McCarty experiment (1944): Isolated DNA as the transforming principle

• Hershey-Chase experiment (1952): DNA carries genetic information, not protein

Watson-Crick Model and Chargraff’s Rules:

• Amount of adenine (A) = thymine (T)

• Amount of cytosine (C) = guanine (G)

• Franklin’s X-ray diffraction: Provided helical structure details

Watson-Crick Structure Characteristics:

• Double helix with antiparallel nucleotide strands

• Sugar-phosphate backbones on outside, nitrogenous bases inside

• Complementary base pairs: A with T, C with G, held by hydrogen bonds

Genome vs. Proteome Size and Organism Complexity:

• Increase in genome size ≠ increased complexity

• Complexity related to gene regulation and protein diversity

Three Classes of DNA:

• Genomic DNA: Complete gene set, heredity

• Mitochondrial DNA: In mitochondria, maternally inherited, energy production

• Plasmid DNA: Circular, found in bacteria, replicates independently, carries survival genes

Factors Influencing DNA Denaturation:

• Temperature, pH levels, salt/chemical concentration

• High temperatures break hydrogen bonds, causing strand separation

DNA Organization into Nucleosomes:

• DNA wrapped around histones, forming nucleosomes

• Nucleosome structure: "beads on a string" with 147 base pairs around core histones

Nucleosomes into Metaphase Chromosomes:

• Further folding and coiling forms condensed metaphase chromosomes

• Important for DNA segregation during cell division

Heterochromatin vs. Euchromatin:

• Heterochromatin: Densely packed, transcriptionally inactive

• Euchromatin: Less condensed, transcriptionally active

Histone Modifications and DNA Availability:

• Acetylation: Relax DNA structure, promote transcription

• Methylation: Can activate or repress transcription

• Regulates DNA accessibility to transcription factors, influencing gene expression.