Students Get handout – potential FRQs

Students Get handout – potential FRQs New seats coming…sit in regular seats first please Genetics problems DUE WEDNESDAY Today: begin Ch 16 Tues: learn Chi-square Wed: Corn lab…using chi-square Thur: lab wrap-up & continue ch 16 Fri: Finish Ch 16 Phones into bins….off or muted….please & thank you!

Chapter 16: The Molecular Basis of Inheritance
Ch 13 – meiosis makes gametes Ch 14 – traits carried in gametes Ch15 – genes found on chromosomes Ch 16 – DNA is the molecule of inheritance How did we learn this?

What evidence did Frederick Griffith have that DNA was the genetic material? Transformation – external DNA is incorporated by a cell which changes the cell’s genotype and phenotype Bacteria of the “S” (smooth) strain of Streptococcus pneumoniae are pathogenic because they have a capsule that protects them from an animal’s defense system. Bacteria of the “R” (rough) strain lack a capsule and are nonpathogenic. Frederick Griffith injected mice with the two strains as shown below: Griffith concluded that the living R bacteria had been transformed into pathogenic S bacteria by an unknown, heritable substance from the dead S cells. EXPERIMENT RESULTS CONCLUSION Living S (control) cells Living R Heat-killed (control) S cells Mixture of heat-killed S cells and living R cells Mouse dies Mouse healthy Living S cells are found in blood sample.

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? - Bacteriophage – viruses that infect bacteria Phage head Tail Tail fiber DNA Bacterial cell 100 nm

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? In their famous 1952 experiment, Alfred Hershey and Martha Chase used radioactive sulfur and phosphorus to trace the fates of the protein and DNA, respectively, of T2 phages that infected bacterial cells. EXPERIMENT Radioactivity (phage protein) in liquid Phage Bacterial cell Radioactive protein Empty protein shell DNA Centrifuge Pellet (bacterial cells and contents) Pellet (phage DNA) in pellet Batch 1: Phages were grown with radioactive sulfur (35S), which was incorporated into phage protein (pink). Batch 2: Phages were phosphorus (32P), which was incorporated into phage DNA (blue). 1 2 3 4 Agitated in a blender to separate phages outside the bacteria from the bacterial cells. Mixed radioactively labeled phages with bacteria. The phages infected the bacterial cells. Centrifuged the mixture so that bacteria formed a pellet at the bottom of the test tube. Measured the radioactivity in the pellet and the liquid

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? Phage proteins remained outside the bacterial cells during infection, while phage DNA entered the cells. When cultured, bacterial cells with radioactive phage DNA released new phages with some radioactive phosphorus. Hershey and Chase concluded that DNA, not protein, functions as the T2 phage’s genetic material. RESULTS CONCLUSION

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? Nucleotide composition Human A – 30.3% T – 30.3% C – 19.9% G – 19.5% Sugar-phosphate backbone Nitrogenous bases 5 end O– O P CH2 5 4 H 3 1 CH3 N Thymine (T) Adenine (A) Cytosine (C) OH 2 Sugar (deoxyribose) 3 end Phosphate Guanine (G) DNA nucleotide Chargaff’s rules A=T C=G Note: 5’ end – phosphate group 3’ end - -OH

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? - NONE – compiled everyone else’s data (a) Rosalind Franklin Franklin’s X-ray diffraction Photograph of DNA (b) Double helix

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? NONE – compiled everyone else’s data Determined double helix from Rosalind Franklin’s data Purine + Purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width Consistent with X-ray data

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? NONE – compiled everyone else’s data Determined double helix from Rosalind Franklin’s data N H O CH3 Sugar Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Figure 16.7 The double helix
OH P H2C T A C G CH2 O– 5 end Hydrogen bond 3 end 0.34 nm 3.4 nm (a) Key features of DNA structure (b) Partial chemical structure (c) Space-filling model 1 nm DNA is antiparallel Hydrogen bonds hold double helix together Now that we know how DNA is shaped & how it fits together…..

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? The basic concept (a) The parent molecule has two complementary strands of DNA Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. (b) The first step in replication is separation of the two DNA strands. (c) Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand. (d) The nucleotides are connected to form the sugar-phosphate backbones of the new strands Each “daughter” DNA molecule consists of one parental strand and one new strand. A C T G But is replication done in a conservative, semi-conservative or dispersive manner?

Students Sickle cell packet in the box Today – Finish Ch 16 – Lab make-up: 3:15PM Monday – Lab notebooks due Chi-square – completed & stapled in…include fly wing problem Mode of inheritance??? Genetics of Corn – full write up Review session 3:15 Tuesday – FRQ – Learning logs due Review session – 7AM Wednesday – MC & Math Phones in bin…muted or off…please & thank you

Essential Questions LO 3.1 The student is able to construct scientific explanations that use the structures and mechanisms of DNA and RNA to support the claim that DNA and, in some cases, that RNA are the primary sources of heritable information. LO 3.2 The student is able to justify the selection of data from historical investigations that support the claim that DNA is the source of heritable information. LO 3.3 The student is able to describe representations and models that illustrate how genetic information is copied for transmission between generations.

Figure 16.10 Three alternative models of DNA replication
Conservative model. The two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix. (a) Semiconserva- tive model. The two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand. (b) Dispersive model. Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA. (c) Parent cell First replication Second Conservative Original strands return together Semi-conservative One original & one new strand Dispersive Original strands are dispersed through new strands The Meselson – Stahl Experiment showed how DNA replicates.

Figure 16.11 Does DNA replication follow the conservative, semiconservative, or dispersive model?
Matthew Meselson and Franklin Stahl cultured E. coli bacteria for several generations on a medium containing nucleotide precursors labeled with a heavy isotope of nitrogen, 15N. The bacteria incorporated the heavy nitrogen into their DNA. The scientists then transferred the bacteria to a medium with only 14N, the lighter, more common isotope of nitrogen. Any new DNA that the bacteria synthesized would be lighter than the parental DNA made in the 15N medium. Meselson and Stahl could distinguish DNA of different densities by centrifuging DNA extracted from the bacteria. EXPERIMENT The bands in these two centrifuge tubes represent the results of centrifuging two DNA samples from the flask in step 2, one sample taken after 20 minutes and one after 40 minutes. RESULTS Bacteria cultured in medium containing 15N transferred to 14N 2 1 DNA sample centrifuged after 20 min (after first replication) 3 after 40 min (after second 4 Less dense More

CONCLUSION Meselson and Stahl concluded that DNA replication follows the semiconservative model by comparing their result to the results predicted by each of the three models in Figure The first replication in the 14N medium produced a band of hybrid (15N–14N) DNA. This result eliminated the conservative model. A second replication produced both light and hybrid DNA, a result that eliminated the dispersive model and supported the semiconservative model. First replication Second replication Conservative model Semiconservative Dispersive

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? How is DNA replicated? Origin of replication - sequence of DNA

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? How is DNA replicated? Origin of replication – sequence of DNA Elongation DNA polymerase 500 bp/sec bacteria, 50 bp/sec in us New base added to 3’end (-OH)…..5’  3’ direction dNTPs provide energy (N = A, C, G, or T)

Figure 16.13 Incorporation of a nucleotide into a DNA strand
New strand Template strand 5’ end 3’ end Sugar A T Base C G P OH Nucleoside triphosphate Pyrophosphate 2 P Phosphate OH DNA polymerase

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? How is DNA replicated? Origin of replication – sequence of DNA Elongation Dealing with antiparallel strands

Overall direction of replication
Figure 16.14 Synthesis of leading and lagging strands during DNA replication Parental DNA DNA pol Ill elongates DNA strands only in the 5  direction. 3 5 2 1 Okazaki fragments DNA pol III Template strand Leading strand Lagging strand 3 DNA ligase Overall direction of replication One new strand, the leading strand, can elongate continuously 5  as the replication fork progresses. The other new strand, the lagging strand must grow in an overall 3  direction by addition of short segments, Okazaki fragments, that grow 5  (numbered here in the order they were made). DNA ligase joins Okazaki fragments by forming a bond between their free ends. This results in a continuous strand. 4

Figure 16.15 Synthesis of the lagging strand
Overall direction of replication 3 5 1 2 DNA ligase forms a bond between the newest DNA and the adjacent DNA of fragment 1. 6 The lagging strand in this region is now complete. 7 DNA pol 1 replaces the RNA with DNA, adding to the 3 end of fragment 2. 5 After the second fragment is primed. DNA pol III adds DNA nucleotides until it reaches the first primer and falls off. 4 After reaching the next RNA primer (not shown), DNA pol III falls off. 3 DNA pol III adds DNA nucleotides to the primer, forming an Okazaki fragment. Primase joins RNA nucleotides into a primer. Template strand RNA primer Okazaki fragment

Figure 16.16 A summary of bacterial DNA replication
Overall direction of replication Helicase unwinds the parental double helix. Molecules of single- strand binding protein stabilize the unwound template strands. The leading strand is synthesized continuously in the 5 3 direction by DNA pol III. Leading strand Origin of replication Lagging OVERVIEW Replication fork DNA pol III Primase Primer DNA pol I DNA ligase 1 2 3 Primase begins synthesis of RNA primer for fifth Okazaki fragment. 4 DNA pol III is completing synthesis of the fourth fragment, when it reaches the RNA primer on the third fragment, it will dissociate, move to the replication fork, and add DNA nucleotides to the 3 end of the fifth fragment primer. 5 DNA pol I removes the primer from the 5 end of the second fragment, replacing it with DNA nucleotides that it adds one by one to the 3’ end of the third fragment. The replacement of the last RNA nucleotide with DNA leaves the sugar- phosphate backbone with a free 3 end. 6 DNA ligase bonds the 3 end of the second fragment to the 5 end of the first fragment. 7 Parental DNA 5 3

Students - Get the graded sickle cell video packet from counter Lab notebooks on the shelf Test tomorrow (MC & math) Learning logs due Review session after school 3:15 & 7 AM Review FRQs & rubrics Phones in the bin….muted or off…please & thank you

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? How is DNA replicated? How is DNA repaired? Proofreading – mismatch repair – DNA polymerase fixes mistakes made during copying Excision repair

Figure 16.17 Nucleotide excision repair of DNA damage
Nuclease DNA polymerase ligase A thymine dimer distorts the DNA molecule. 1 Repair synthesis by a DNA polymerase fills in the missing nucleotides. 3 DNA ligase seals the Free end of the new DNA To the old DNA, making the strand complete. 4 A nuclease enzyme cuts the damaged DNA strand at two points and the damaged section is removed. 2 Thymine dimers from UV damage

What evidence did Frederick Griffith have that DNA was the genetic material? How did Hershey & Chase determine that DNA was the genetic material? What was Chargaff’s contribution? What experiment did Watson & Crick do? How does DNA replicate itself? How is DNA replicated? How is DNA repaired? What happens at the end of chromosomes (telomere)? Recall DNA polymerase works 5’ → 3’ direction After RNA primer is removed, chromosome is shortened

Figure 16.18 Shortening of the ends of linear DNA molecules
End of parental DNA strands Leading strand Lagging strand Last fragment Previous fragment RNA primer Removal of primers and replacement with DNA where a 3 end is available Primer removed but cannot be replaced with DNA because no 3 end available for DNA polymerase Second round of replication New leading strand New lagging strand 5 Further rounds Shorter and shorter daughter molecules 5 3

primer Telomerase active in germ line cells & newborns to prevent extensive shortening -extends telomere a bit -has its own RNA - complementary to telomere - serves as primer 2009 Nobel Prize in Medicine - for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase

Students Spread out – 2 students per table Stack learning logs in a pile on your table Get calculator from counter Test consists of 4 items MC packet (Q 1 – 31) GREEN sheet (Q 32 – 36) Do NOT write on this!! Thank you. ½ sheet with 2 math questions GREEN scantron…indicate test form A or B Cans Bring cans for tomorrow Transport tomorrow Phones in the bin…muted or off…please & thank you

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