Module 3 Practice Problems The following slides contain questions designed to help you practice solving problems based on the material in this unit These problems are not exhaustive and do not cover all the material in this unit Practice Problem Important Experiments Major Question Simple Idea Key Observations Conclusions Name of Investigator Meischer Yanofsky Griffith Avery Macleod and McCarty Hershey and Chase Chargaff Wilkins and Franklin Watson and Crick Practice Problem Important Experiments Major Question Simple Idea Conclusions Name of Investigator Meischer Yanofsky Griffith Why do nonvirulent strains of S pneumonia become virulent when exposed to dead virulent strains Avery Macleod and McCarty What is the cause of transformation from Griffith s experiments Hershey and Chase What are the infectious parts of bacteriophages Can an extract from dead bacterial cells genetically transform living cells Eliminate each component of bacteria one at a time If the nonvirulent strain is transformed the components removed are not needed for transformation Radiolabel phages protein coat 35S or DNA 32P Observe what gets passed on Key Observations First to isolate DNA Changes in DNA and protein are colinear S strain kills mice Heat killed S strain does not R strain does not kill mice Heated S R strain does kill kill mice mice Only treatment of the S cell extract with DNase kept the extract from transforming the R cells The unknown process that changes the avirulent strain to a virulent strain is called Transformation DNA is required for transformation The bacteria had a lot of 32P and very little 35S after phage infection DNA is the infectious part of bacteriophages Practice Problem Important Experiments Name of Investigator Chargaff Major Question What is the base composition of DNA and is there a pattern Simple Idea Key Observations Conclusions Did a quantitative analysis of DNA base pairs Base composition from different species in table G C amount A T amount Wilkins and Franklin What is the crystalline structure of DNA X ray crystallography study of DNA X ray scattered picture of crystallized DNA looks like a helix 2 nm in diameter with 2 regularities 3 4 nm and 0 34 nm Structure of DNA is helical w more than one helix with repeating patterns Antiparallel strands Pyrimidines pair with purines Watson and Crick What is the structure of DNA Used Chargaff s and Franklin s data others to determine DNA structure KNOWN Chargaff Ratios DNA is helical Franklin Hydrogen bonds set the Sugars and phosphates on the outside of the helix Alternating major and minor structure of the DNA grooves 2 nm wide 3 4 nm per turn of helix 0 34 nm between adjacent bases ETC Practice Problem DNA structure 1 Label 3 end 5 end Phosphodiester bond Purine Pyrimidine O P O O O H H O P O H O H H H O O H H H CH 2 O H O P O H O H O P O CH2 O O O H H H CH3 N N O O H O CH2 H N N N H N N O O O P O CH2 H O H O P O H H O N N CH2 O H CH3 PO O N N H N N H N N N O N H H H N H O O N N H N N O H H H O H H O H O O CH2 H O H H H O H O P O Practice Problem DNA structure 1 Label 3 end 5 end Phosphodiester bond Purine Pyrimidine 3 end Phosphodiester bond H H CH3 H Pyrimidine H O N N H O H N N N Purine N N O P O O O H O CH2 H O P O H O O H H CH 2 O H O P O H O H H H O H O P O CH2 O O O O H H H O O O O P O CH2 H O H O P O H 5 end Phosphodiester bond O H H N Pyrimidine N H H CH3 CH2 O N N Purine N N N H N H O H Pyrimidine N H N O O N N Purine N N H H N H H O O CH2 H O H O H H H O H O P O PO O Phosphodiester bond 3 end Phosphodiester bond 5 end Practice problem DNA structure 2 If the GC content of a DNA molecule it 56 what are the percentages of the four bases in this molecule Practice problem DNA structure 2 If the GC content of a DNA molecule it 56 what are the percentages of the four bases in this molecule 28 G 28 C 22 A 22 T Practice problem DNA structure 3 Imagine you are a student in Alfred Hershey and Martha Chase s lab in the late 1940s You are given five test tubes containing E coli bacteria that were infected with T2 bacteriophage that have been labeled with either 32P or 35S Unfortunately you forgot to mark the tubes and are now uncertain which were labeled with 32P and which with 35S You place the contents of the each tube in a blender and turn it on for a few seconds to shear off the protein coats You then centrifuge the contents to separate the protein coats and the cells You check for the presence of radioactivity and obtain the following results Which tubes contained E coli infected with 32P labeled phage Tube number 1 2 3 4 5 Presence of radioactivity in cells protein coats protein coats cells cells Pierce 10 24 6th ed Practice problem DNA structure 3 Imagine you are a student in Alfred Hershey and Martha Chase s lab in the late 1940s You are given five test tubes containing E coli bacteria that were infected with T2 bacteriophage that have been labeled with either 32P or 35S Unfortunately you forgot to mark the tubes and are now uncertain which were labeled with 32P and which with 35S You place the contents of the each tube in a blender and turn it on for a few seconds to shear off the protein coats You then centrifuge the contents to separate the protein coats and the cells You check for the presence of radioactivity and obtain the following results Which tubes contained E coli infected with 32P labeled phage Tube number 1 2 3 4 5 Presence of radioactivity in cells protein coats protein coats cells cells Tubes 1 4 and 5 The DNA of the bacteriophage contains phosphorous and the protein contains sulfur When the bacteriophages infect the cell they inject their DNA into the cell but the protein coats stay on the surface of the cell The protein coats are sheared off in the blender while the cells with the DNA pellet at the bottom of the tube Thus cells infected with 35S labeled bacteriophage will have radioactivity associated with the protein coats whereas those cells infected with 32Plabeled bacteriophage will have radioactivity associated with the cells Pierce 10 24 6th ed Practice problem DNA structure 5 What results would you expect if …