Unit 2: section 3. Chapter 10: Biochemistry of the Genome

Frederick Griffith's Experiment

• Demonstrated the "transformation principle", a process where dead bacteria can transfer genetic material to live bacteria, altering their characteristics.
• Used two strains of Streptococcus pneumoniae:
  • S strain: Smooth, virulent, and causes pneumonia.
  • R strain: Rough, non-virulent, and does not cause pneumonia.
• Griffith's experiment showed that heat-killed S strain bacteria could transform live R strain bacteria into virulent S strain bacteria when injected into mice.

The Difference between S and R Strains

• S strain: Smooth, virulent, and has a polysaccharide capsule that protects it from the host's immune system.
• R strain: Rough, non-virulent, and lacks the capsule, making it susceptible to the host's immune system.

Beadle and Tatum's One Gene-One Enzyme Hypothesis

• Proposed that each gene controls the production of a specific enzyme.
• Used the mold Neurospora crassa to study the role of genes in metabolic pathways.
• They demonstrated that each mutation in the mold affected a specific metabolic pathway, supporting their hypothesis.

Avery, MacLeod, and McCarty's Key Finding

• Confirmed that DNA, not protein, is the genetic material responsible for the transformation observed by Griffith.
• Their experiments built upon Griffith's work by isolating and purifying different components of the heat-killed S strain bacteria.
• They found that only DNA was able to transform the R strain into the S strain, proving its role as the genetic material.

Hershey and Chase Experiment: Confirming DNA as the Genetic Material

• Utilized bacteriophages (viruses that infect bacteria) and radioactive labeling to further confirm DNA as the genetic material.
• They labeled the DNA of the bacteriophage with radioactive phosphorus and the protein coat with radioactive sulfur.
• Upon infection, they found that only the radioactive phosphorus (DNA) was transferred to the bacteria, indicating that DNA is the material responsible for carrying genetic information.

Watson and Crick's Discovery

• Determined the double helix structure of DNA.
• Their model explained how DNA replicates and how genetic information is encoded.

Key Differences between DNA and RNA

• DNA is double-stranded, contains deoxyribose sugar, and uses thymine as a base.
• RNA is single-stranded, contains ribose sugar, and uses uracil as a base.

Definitions

• Genome: The complete set of genetic material in an organism.
• Gene: A segment of DNA that codes for a specific protein.
• Phenotype: The observable traits of an organism, influenced by its genotype and environment.
• Genotype: The genetic makeup of an organism.

The Impact of Environment on Phenotype

• Phenotype can be influenced by environmental factors.
• Examples:
  • Temperature can affect fur color in animals.
  • Light availability can affect plant growth and development.

DNA Organization in Bacteria

• Bacterial DNA is organized within the nucleoid region, a region within the cytoplasm.
• To fit inside the cell, DNA is supercoiled into loop domains, forming a compact structure.

Plasmids

• Small, circular pieces of DNA found in bacteria, separate from their main chromosome.
• Often carry genes that provide advantages, such as:
  • Antibiotic resistance.
  • Virulence factors.