DNA: the Molecular Basis of Inheritance Chapter 11

DNA: the genetic material In the 1860’s Mendel verified that traits were inheritable components passed from parent to offspring. In the 1860’s Mendel verified that traits were inheritable components passed from parent to offspring. These traits seemed to obey certain laws. What were the laws that inheritable traits obeyed? These traits seemed to obey certain laws. What were the laws that inheritable traits obeyed?

By the 1920’s it had been established that chromosomes were the basis of inheritance. Scientists understood it was something in chromosomes that caused the multitudinous variety of organism present on earth. What are the two components of chromosomes? What is the structure of chromosomes? By the 1920’s it had been established that chromosomes were the basis of inheritance. Scientists understood it was something in chromosomes that caused the multitudinous variety of organism present on earth. What are the two components of chromosomes? What is the structure of chromosomes? DNA: the genetic material

The structure of chromosomes:

The Griffith Experiment: Showed that DNA was the material that transferred inheritable traits Showed that DNA was the material that transferred inheritable traits Was a “lucky” find Was a “lucky” find Griffith’s experiment with Streptococcus pneumoniae Griffith’s experiment with Streptococcus pneumoniae Griffith’s experiment with Streptococcus pneumoniae Griffith’s experiment with Streptococcus pneumoniae His experiment was confirmed by Oswald Avery in 1944 His experiment was confirmed by Oswald Avery in 1944 What was the significance of these two experiments? What was the significance of these two experiments?

DNA or Protein? Why would protein be a good candidate for passing on of hereditary material? Why would protein be a good candidate for passing on of hereditary material? Why was DNA not thought to be a good candidate? Why was DNA not thought to be a good candidate? How was DNA shown to be the real “power” behind inheritance once and for all? How was DNA shown to be the real “power” behind inheritance once and for all? Hershey and Chase experiment Hershey and Chase experiment

Hershey-Chase experiment:

Watson and Crick and Chargaff and Franklin and Wilkins and… Using the information gathered by Erwin Chargaff, Maurice Wilkins and Rosalind Franklin, Francis Crick and James Watson were able to deduce the structure of DNA: a double helix surrounding paired nitrogen bases Using the information gathered by Erwin Chargaff, Maurice Wilkins and Rosalind Franklin, Francis Crick and James Watson were able to deduce the structure of DNA: a double helix surrounding paired nitrogen bases Back ground and explanation of DNA structure Back ground and explanation of DNA structure Back ground and explanation of DNA structure Back ground and explanation of DNA structure

The nature of DNA replication “ It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” - J.D. Watson & F.H.C. Crick in “Molecular Structure of Nucleic Acids: A Structure for Deoxynucleic acids”

How does DNA replicate? The two DNA strands by being complementary to one another serve as a template for new strands (semiconservative model) The two DNA strands by being complementary to one another serve as a template for new strands (semiconservative model) Other models of replication had to be rejected (conservative, and dispersive) Other models of replication had to be rejected (conservative, and dispersive) Meselson and Stahl’s experiment Meselson and Stahl’s experiment Meselson and Stahl’s experiment Meselson and Stahl’s experiment

The enzymes of replication Helicase Helicase Primase Primase DNA polymerase I DNA polymerase I DNA polynerase III DNA polynerase III DNA ligase DNA ligase Single strand binding protein Single strand binding protein DNA topoisomerase DNA topoisomerase Telomerase Telomerase

Telomeres Repetitive strands at the end of chromosomes Repetitive strands at the end of chromosomes Human sequence is TTAGGG repeated about 2500 times Human sequence is TTAGGG repeated about 2500 times Per replication each human loses about base pairs Per replication each human loses about base pairs Cells die after about divisions Cells die after about divisions Telomerase regenerates telomeres Telomerase regenerates telomeres

DNA proof reading and repair 1 base pair in 10 6 is mismatched 1 base pair in 10 6 is mismatched Result would be 1000 mutations per cell division Result would be 1000 mutations per cell division Mechanisms are in place to proofread and repair DNA Mechanisms are in place to proofread and repair DNA

DNA proofreading DNA polymerase “reads” DNA strand and finds mismatched bases. DNA polymerase “reads” DNA strand and finds mismatched bases. The mismatched base is excised and replaced The mismatched base is excised and replaced Lowers the error rate to one in Lowers the error rate to one in How does the DNA polymerase “know” which strand is faulty? How does the DNA polymerase “know” which strand is faulty?