DNA Chapter 12

First Question- Early 1900s What molecule carries genetic information?

Griffith Experiment: Background Info In 1928, Frederick Griffith was researching to try to explain how bacteria makes people get sick, studying pneumonia particularly. He isolated two strains of bacteria in mice. – S strain: smooth colonies, disease causing – R strain: rough colonies, harmless

Griffith’s Experiments

Explanation Bacterial transformation The ability to cause disease was inherited by the offspring through genes.

Avery’s Further Studies In 1944, Oswald Avery determined that DNA was the transforming factor in bacteria by destroying proteins, lipids, carbohydrates, and some other molecules and transformation still occurred. The experiment was repeated where DNA was destroyed and transformation did not occur.

Bacteriophage: Background Info

The Hershey-Chase Experiment Grew viruses containing radioactive 32 P and 35 S to use as markers. The protein coat of the virus contains almost no P and DNA contains no S. Therefore, the experiment could reveal whether the protein coat or DNA entered the bacteria cell.

Conclusion Since only radioactive phosphorus was found in the cells, DNA is the genetic material of the bacteriophage.

The Role of DNA Storing information Copying information Transmitting information

The Components of DNA DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

Nucleotides Nucleotides have three components: a 5- carbon sugar (called deoxyribose), a phosphate group, and a nitrogenous base.

Chargaff’s Rule In ANY organism, – the amount of adenine=thymine – the amount of cytosine=guanine What does this suggest about the relationship among these bases?

Rosalind Franklin’s X-rays Early 1950s

Watson and Crick’s Model 1953

DNA’s Antiparallel Arrangement

DNA Replication Summary DNA must be replicated during late interphase to ensure that each cell has its own copy of DNA after division. During replication, the DNA molecule splits into two strands. Two new complementary strands are made using the original DNA strands as templates.

DNA Replication Details 1. The two strands of the double helix are unzipped by an enzyme called helicase, forming two replication forks.

Details Continued 2. The enzyme DNA polymerase joins nucleotides to produce a new strand of DNA. Due to the antiparallel nature of DNA, synthesis occurs in two different directions.

Details Continued 3. DNA polymerase checks for replication errors. 2Nw