DNA: Structure and Replication Chapter 7

DNA: The Genetic Material Before Watson and Crick solved the structure of DNA, other scientists had discovered that DNA was the genetic material Reminders from what we have already covered Genes are hereditary factors One gene one enzyme hypothesis (WHO?) Genes located on chromosomes (LOCATION?) Chromosomes consist of DNA and proteins

Discovery of Transformation: Griffith Streptococcus pneumoniae What is the difference between S and R? Protective polysaccharide coat Fredrick Griffith made the discover using S and R strains of Streptococcus pneumoniae. This is the S strain bacteria that normally causes pneumonia in humans and is normal lethal in mice. But the R strain of Strep. Is less virulent and therefore less able to cause disease or death. protective polysaccharide coat

Which part of the cell is the transforming agent? Avery, Macleod and McCarty Avery, Macleod and McCarty

Hershey – Chase experiment Amino acids (aa) with sulfur: methionine and cysteine DNA has phosphorus in its backbone The Hershey-Chase experiment demonstrated that the genetic material of phages is DNA, not protein. The experiment uses two sets of T2 bacteriophage. In one set, the protein coat is labeled with radioactive sulfur (35S), not found in DNA. In the other set, the DNA is labeled with radioactive phosphorus (32P), not found in amino acids. Only the 32P is recovered from the E. coli, indicating that DNA is the agent necessary for the production of new phages.

Concept question Smooth (S) and rough (R) strains of Streptococcus pneumonia are distinct because of their ability to cause illness (death in rodents). This trait is controlled by genes that regulate: A) the production of a protective polysaccharide coat (capsule) around each cell. B) the bacterial ability to penetrate through the membrane of animal cells. C) the speed of bacterial growth. D) the metabolic rate of microbial glycolysis.

DNA structure THREE CHEMICAL COMPONENTS Phosphate Sugar - deoxyribose Nitrogen Base – one of four bases What is the difference between phosphate and phosphorus?

4 Bases

Concept check… Mendel identified evidence for the location of genes on separate structures (chromosomes) through his: A) electrophoresis experiments. B) purification of chromosomes from pea plants. C) identification of dominant and recessive alleles of genes. D) identification of independent assortment of distinct genes during meiosis.

Chargaff’s rules of base composition Pyrimidine = Purines T + C = G + A 27.8

Concept question Alfred Hershey and Martha Chase examined transformation using bacteriophage and bacterial cells. In these experiments, they used radioactivity to label nucleic acids (in this case DNA) and proteins. What does radioactive sulfur and phosphate specifically label? A) Sulfur labels DNA, and phosphate labels protein. B) Sulfur labels both protein and DNA. C) Phosphate labels both protein and DNA. D) Sulfur labels protein, and phosphate labels DNA.

Rosaline Franklin Died of bronchopneumonia, secondary carcinomatosis, and ovarian cancer. Exposure to X-ray radiation is considered to be a possible factor in her illness Watson and Crick used this image to help solve the structure of DNA Died of bronchopneumonia, secondary carcinomatosis, and ovarian cancer. Exposure to X-ray radiation is sometimes considered to be a possible factor in her illness Carcinomatosis is described as a condition in which multiple carcinomas develop simultaneously, usually after dissemination from a primary source.

The double helix Anti-parallel Bases 0.34 nm apart 10 bases per turn Nucleoside vs nucleotide

DNA stability A = T G Ξ C DNA with higher GC content is more stable. This can be demonstrated in a lab….use heat to separate or denature DNA. Higher GC content requires increased temperature for denaturation.

How does DNA replicate? Meselson-Stahl experiment Synthesize DNA with heavy N15 Change DNA synthesis to light N14

1 2 3

Oswald Avery and colleagues strengthened scientific support that DNA was the transforming factor by replicating the Griffith experiment with some important differences in experimental design. They found that the enzyme ______________ was effective at destroying the transforming capacity of S strain biomolecules. A) protease B) RNase C) DNase D) polysaccharide-destroying enzymes

How long is one turn of DNA? 0.34nm 3.4nm 3.8nm 3.4pm