DNA: The Genetic Material. Chapter 14. The Genetic Material. Griffith’s conclusion: - information specifying virulence passed from the dead S strain cells into the live R strain cells - Griffith called the transfer of this information transformation. The Genetic Material.
DNA: The Genetic Material
- information specifying virulence passed from the dead S strain cells into the live R strain cells
- Griffith called the transfer of this information transformation
Avery, MacLeod, & McCarty, 1944
repeated Griffith’s experiment using purified cell extracts and discovered:
- removal of all protein from the transforming material did not destroy its ability to transform R strain cells
- DNA-digesting enzymes destroyed all transforming ability
- the transforming material is DNA
Hershey & Chase, 1952
- investigated bacteriophages: viruses that infect bacteria
- the bacteriophage was composed of only DNA and protein
- they wanted to determine which of these molecules is the genetic material that is injected into the bacteria
Determining the 3-dimmensional structure of DNA involved the work of a few scientists:
This is known as Chargaff’s Rules
Rosalind Franklin and Maurice Wilkins
James Watson and Francis Crick, 1953
The double helix consists of:
The two strands of nucleotides are antiparallel to each other
The two strands wrap around each other to create the helical shape of the molecule.
Matthew Meselson & Franklin Stahl, 1958
investigated the process of DNA replication
considered 3 possible mechanisms:
Bacterial cells were grown in a heavy isotope of nitrogen, 15N
all the DNA incorporated 15N
cells were switched to media containing lighter 14N
DNA was extracted from the cells at various time intervals
The DNA from different time points was analyzed for ratio of 15N to 14N it contained
After 1 round of DNA replication, the DNA consisted of a 14N-15N hybrid molecule
After 2 rounds of replication, the DNA contained 2 types of molecules:
Meselson and Stahl concluded that the mechanism of DNA replication is the semiconservative model.
Each strand of DNA acts as a template for the synthesis of a new strand.
The chromosome of a prokaryote is a circular molecule of DNA.
Replication begins at one origin of replication and proceeds in both directions around the chromosome.
The double helix is unwound by the enzyme helicase
DNA polymerase III (pol III) is the main polymerase responsible for the majority of DNA synthesis
DNA polymerase III adds nucleotides to the 3’ end of the daughter strand of DNA
The larger size and complex packaging of eukaryotic chromosomes means they must be replicated from multiple origins of replication.
The enzymes of eukaryotic DNA replication are more complex than those of prokaryotic cells.
Synthesizing the ends of the chromosomes is difficult because of the lack of a primer.
With each round of DNA replication, the linear eukaryotic chromosome becomes shorter.
telomeres – repeated DNA sequence on the ends of eukaryotic chromosomes
telomerase contains an RNA region that is used as a template so a DNA primer can be produced
- DNA-damaging agents
- repair mechanisms
- specific vs. nonspecific mechanisms
Mistakes during DNA replication can lead to changes in the DNA sequence and DNA damage.
DNA can also be damaged by chemical or physical agents called mutagens.
Repair mechanisms may be used to correct these problems.
DNA repair mechanisms can be: