Chapter 12 DNA RNA Interest Grabber Section 12

Chapter 12 DNA & RNA

Interest Grabber Section 12 -1 l. Order! l. Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?

I. DNA A. Griffith & Transformation l Frederick Griffith was trying to figure out how bacteria made people sick-how they cause a certain type of pneumonia. l He isolated 2 strains(types) from mice-both cultured well, but only one caused pneumonia. The culture of the disease causing bacteria were _________colonies while the other was l rough. smooth

l 1 -Griffith’s experiments (1928) ¡ Mice injected w/ disease –causing strain got sick and died and nothing happened if injected w/other strain…He wondered if the disease-causing type made a toxin…? ¡ So he took some of disease strain and heated to kill bacteria and then injected into mice…. mice survived suggesting it was not a toxin producing disease

Figure 12– 2 Griffith’s Experiment Section 12 -1 Heat-killed, disease -causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria Dies of pneumonia Control (no growth) (smooth colonies) Lives Live, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumonia

l l 2 -Transformation He mixed his heat –killed w/ live harmless bacteria and injected into mice…. . ____________ Somehow the disease –causing strain passed their disease capacity to harmless bacteria…. . disease – causing strain found in lungs He called this changing of one bacteria by the genes of another ___________. . Thus a factor(gene) from heat killed disease –causing strain was passed on. Mice developed pneumonia transformation

B. Avery & DNA Team of scientists lead by Avery in 1944 repeated Griffith’s experiment in order to determine which molecule was responsible for the transformation. l They made an extract from the heat-killed bacteria and treated it w/enzymes that kill proteins, lipids and other molecules, inc. RNA l

Avery cont’d transformation __________still occurred so the above molecules were not responsible for transformation l They repeated the experiment but used enzymes that kill______, stopping transformation…. DNA l Therefore ____caused the transformation and thus stores and transmits genetic info l

C. The Hershey –Chase Experiment 1952 -Alfred Hershey and Martha Chase studied viruses-disease-causing particles smaller than a cell. l ___________-virus that infects bacteria. They have a DNA or RNA core and a protein coat…They attach to the surface of a bacterium and inject genetic info into cell. The viral genes act to produce many new bacteriophages and eventually destroy bacterial cell, w/_______bursting out. l bacteriophage viruses

They grew viruses in cultures containing _________________, mixed them w/bacteria and waited a few min. for viruses to inject genetic material. l Then they separated the bacteria from the viruses and tested bacteria for radioactive marker…. . nearly all the radioactivity was P-32 -found in _____---thus concluding it was the genetic material was DNA ! l Radioactive markers DNA

Figure 12– 4 Hershey-Chase Experiment Section 12 -1 Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium

D. The Components and Structure of DNA Scientists questioned how the DNA molecule could do three things 1)carry info from 1 generation to the next 2)putting that info to work and 3)could be easily copied l DNA is a long molecule made of units called ______________________l nucleotides

l The nucleotide is made of 3 basic parts: ___________(sugar), a phosphate group and a_________________ deoxyribose Nitrogenous base

2 nitrogenous bases are purines(have 2 rings): ______________(A)and_______ (G) l 2 other nitrogenous bases are pyrimidines (have 1 ring): __________(C)and l ______________(T) Adenine , guanine Cytosine and thymine --backbone made by sugar and phosphate w/ bases sticking out sideways

Figure 12– 5 DNA Nucleotides Section 12 -1 Purines Adenine Guanine Pyrimidines Cytosine Thymine Phosphate group Deoxyribose

l 1 -____________Rules-discovered that %’s of Cytosine and guanine were almost equal in DNA and the same was true for adenine and thymine…. Thus A pairs w/T and C w/ G-BASE PAIRING Chargaff’s Rules

Percentage of Bases in Four Organisms Section 12 -1 Source of DNA A T G C Streptococcus 29. 8 31. 6 20. 5 18. 0 Yeast 31. 3 32. 9 18. 7 17. 1 Herring 27. 8 27. 5 22. 2 22. 6 Human 30. 9 29. 4 19. 9 19. 8

$l 2 - X-ray evidence-1950’s –Rosalind Franklin used X-ray diffraction to learn about DNA$

l 2 - X-ray evidence-1950’s –Rosalind Franklin used X-ray diffraction to learn about DNA structure ----The scattered X pattern seen begins to show the _____-partial TWISTED STRUCTURE of DNA helix

¡ l l 3 ---Double helix_ Watson and Crick -2 strands wound around each other---like the twisted ladder or spiral staircase Strands held together by H-bonds

Figure 12– 7 Structure of DNA Section 12 -1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)