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How did scientists come to understand DNA?

How did scientists come to understand DNA?. Chapter 11.1. Lesson Objectives. At the end of this lesson, YOU will be able to: Discussion the contributions of various scientists as they work to construct the model of genetic inheritance. Describe the structure of the molecule DNA.

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How did scientists come to understand DNA?

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  1. How did scientists come to understand DNA? Chapter 11.1

  2. Lesson Objectives • At the end of this lesson, YOU will be able to: • Discussion the contributions of various scientists as they work to construct the model of genetic inheritance. • Describe the structure of the molecule DNA.

  3. The Discovery of DNA • Hereditary information must be passed from parent to child. • Between the 1920’s and the 1950’s, the race was on to discover the molecules that makes us who we are.

  4. Griffith (1928) • Worked with bacteria and mice • Injected mice with two types of bacteria to record the results. http://www.kancoll.org/books/cutler/douglas/griffith.jpg

  5. Griffith’s Experiment • Disease-Causing Bacteria Mouse Dies inject mouse • Harmless Bacteria Mouse Lives inject mouse

  6. inject mouse inject mouse Griffith’s Experiment Heat-Killed Disease-Causing Bacteria Mouse Lives Heat-Killed Disease-Causing + Harmless Mouse Dies

  7. Griffith’s Results • Some genetic material was passed from the disease-causing bacteria to the harmless bacteria. • Transformation • When genetic material from one bacterial strain replaces the DNA of another strain. http://en.wikipedia.org/wiki/Image:Griffith_experiment.svg

  8. Repeated Griffith’s experiment with an important difference. Used enzymes to destroy specific molecules in each experiment: Avery, McCarty, MacLeod (1943) Oswald Avery http://history.nih.gov/exhibits/nirenberg/images/photos/03_avery_pu.jpg

  9. Avery, McCarty, MacLeod • The experiment • When they destroyed carbohydrates and lipids, transformation occurred. • When they destroyed proteins, transformation occurred. • When they destroyed RNA, transformation occurred. • When they destroyed DNA, transformation DID NOT occur. • They determined that DNA stores and transmits genetic information.

  10. Experimented with bacteriophages. A bacteriophage is a VIRUS that affects BACTERIA. A virus is made of DNA and a protein coat. Hershey and Chase (1950) http://www2.carthage.edu/~pfaffle/hgp/ChaseHershey_1953.jpg http://bioweb.wku.edu/courses/BIOL115/Wyatt/HIV/lambaphage.gif

  11. Hershey and Chase

  12. The Experiment They labeled DNA with radioactive phosphorous (P32). They labeled the protein coat with radioactive sulfur (S35). Hershey and Chase S35 P32 Bacterium

  13. The Results Radioactive Sulfur was not found in the bacterium. Radioactive Phosphorus was found in the bacterium. Because only DNA was found, the results confirmed that DNA stores and transmits genetic information. Hershey and Chase P32

  14. Analyzed samples of DNA from many species and noticed a simple pattern. The number of Adenines equals the number of Thymines. The number of Cytosines equals the number of Guanines Chargaff http://www.amphilsoc.org/library/mole/c/chargaff.jpg

  15. Chargaff

  16. Used X-ray Crystallography to get the best picture of the molecule of DNA. Used by Watson and Crick to determine the structure of DNA. Rosalind Franklin http://www.voanews.com/specialenglish/Archive/images/uwinnipeg.ca_rosalind_franklin_x-ray_picture_dna_3march03_se.jpg http://www.physics.ucla.edu/~cwp/images/franklin/franklin1.jpg

  17. Determined the structure of DNA in 1953. By analyzing Franklin’s picture Watson and Crick determined: Sugar and Phosphate make up the backbone. Bases make up the rungs. James Watson and Francis Crick Watson Crick http://www.watsoncrombie.com/wcmodel.jpg

  18. Their Discovery The shape of DNA is a double helix. The two strands of DNA are connected by hydrogen bonds. Follows Pairing Rules A’s pair with T’s G’s pair with C’s Watson and Crick http://instruct.westvalley.edu/svensson/CellsandGenes/dna-structure[1].gif

  19. The building blocks of DNA are nucleotides. Five-Carbon Sugar called Deoxyribose. Phosphate Group Nitrogenous Base DNA (Deoxyribonucleic Acid) Base P Five-Carbon Sugar (deoxyribose)

  20. The Structure of DNA • Types of Nucleotides • Purines (2 rings) • Adenine (A) • Guanine (G) • Pyrimadines (1 ring) • Cytosine (C) • Thymine (T) http://www.voanews.com/specialenglish/Archive/images/uwinnipeg.ca_rosalind_franklin_x-ray_picture_dna_3march03_se.jpg

  21. The Structure of DNA S C G • The DNA molecule forms a Double Helix. • Two strands twist around each other. • Complimentary Base Pairs: • A = T and G = C • Connected by Hydrogen Bonds P S A T P S A T Sugar Phosphate Backbone P S T A P S G C Weak Hydrogen Bonds

  22. DNA Replication DNA Polymerase • DNA holds the genetic information that must be passed onto the next generation. • Process: • Helicase unzips the DNA strand. • DNA Polymerase inserts the complimentary base on the opened strand. • Result: • Two identical strands of DNA • Each is half old and half new (Semi-Conservative) Helicase

  23. DNA Replication • Give me the complimentary DNA strand: • ATTCCGTAG • TGTACTGTA • GTAATGGAC • ACCTGATGG

  24. How does DNA hold the code for and direct the making of proteins? Section 11.2

  25. The Blueprint of Life • DNA contains the code to make all of the proteins in your body. • DNA directs the process of turning the code into proteins. http://www.calligraph.com/cyberscribes/Resources/lorna2cl.jpeg http://www.scq.ubc.ca/wp-content/dna.gif http://www.uucinch.org/UN-History/U-BuildingOurDream/Blueprint.gif

  26. Made of the building blocks called AMINO ACIDS. The exact order of the amino acids determines the type of protein. Made by the ribosomes. Proteins

  27. Remember that DNA is made of the building blocks, nucleotides. DNA has four different nucleotides A, T, C, G The order of nucleotides along the DNA chain, determines what amino acids are put into the protein chain. DNA is found in the nucleus. Nothing to Write on this Slide DNA

  28. Nothing to Write on this Slide The Genetic Code A T C G TREAT • The English Alphabet has 26 letters that can be put into any order to make any number of words. • The DNA Alphabet has 4 letters that must code for 22 different amino acids.

  29. The Genetic Code A T C G • The order of the nucleotides determines the order of amino acids. • Every three letters of DNA are called a triplet. • Each triplet codes for a specific amino acids. • The genetic code is hidden within the triplets of DNA. AA AT AC AG TA TT TC TG CA CT CC CG GA GT GC GG A C C

  30. The Genetic Code • A gene is a piece of DNA that codes for a specific protein. • A series of triplets codes for a specific protein. • Change the gene and change the protein. http://www.epilepsyfoundation.org/research/images/chromosome.gif http://museumvictoria.com.au/scidiscovery/images/mn002491_w371.jpg http://www.northmason.wednet.edu/projects/gifs/genes.gif

  31. DNA is too large to leave the nucleus to make the proteins. The RNA holds the information of a single gene to make a single protein. RNA is single-stranded RNA contains the sugar ribose RNA uses the base, Uracil (U) instead of T. Ribonucleic Acid (RNA)

  32. There are three types of RNA that work together to make proteins. Messenger RNA (mRNA) copies the code of DNA and carries the message to the cytoplasm. Transfer RNA (tRNA) brings the necessary amino acid to the ribosome. Ribosomal RNA (rRNA) makes up a large portion of the ribosome. mRNA tRNA RNA

  33. The Central Dogma of Molecular Biology

  34. Protein Synthesis • The assembly of amino acids in the order specified by the DNA code. • Protein synthesis occurs in two major steps: • Transcription • Translation

  35. Transcription • The DNA code is copied into shorter segments of mRNA. • Process • The DNA strand is unzipped • mRNA is made with complementary base pairing rules. • Occurs in the nucleus.

  36. Example Transcription DNA RNA DNA RNA DNA RNA CTAATGTCA GAUUACAGU ATTACGTGG UAAUGCACC ATCCGTAAT UAGGCAUUA

  37. Translation • The assembly of amino acids from the RNA code. • Process: • Each mRNA codon codes for a specific amino acid. • The tRNA matches the amino acid using its anti-codon. • Occurs at the ribosome in the cytoplasm. http://westlakems.wcpss.net/eagles/science/HBS/HBS_articles/protein_synthesis/rna_trans.gif

  38. Translation • Each mRNA codon codes for a specific amino acid. • The order of codons puts the amino acids in order. • Using the codon chart, you can translate the mRNA. • The appropriate amino acid is carried by the tRNA to the ribosome. • tRNA attaches the amino acid by matching up the anti-codon to the codon. http://www.okc.cc.ok.us/biologylabs/Images/DNA_images/translation.gif http://westlakems.wcpss.net/eagles/science/HBS/HBS_articles/protein_synthesis/rna_trans.gif

  39. Translation • How to Read the Codon Chart: • Obtain a Codon of mRNA, for example AUG. • The first base is found on the left side of the chart (A) so we begin on the third row down. • The second base is found on the top, so we combine the two and we are in the first box of the third row. • The third base is on the right side and gives you the row with in the third box. • In this case, AUG codes for Methionine, which is also the start codon.

  40. Practice Translation AA mRNA mRNA AA GCCAAUUCU AAGUUAGUU Alanine Lysine Leucine Asparagine Valine Serine

  41. Protein Synthesis

  42. Ala Thr Ala Trp Arg Asn Ser Stop Practice Protein Synthesis DNA CGA TGA CGG ACC GCT TTA AGA ATT Transcription GCU ACU GCC UGG CGA AAU UCU UAA mRNA Translation Protein

  43. Protein Synthesis Diagram mRNA Protein Amino Acid DNA Ribosome Transcription tRNA Nucleus Anti-Codon mRNA Translation Codon

  44. Time Trials AUU-CGC-ACC-UGU-ACG Iso - Arg - Thr – Cys - Thr GCA-GUA-CCC-GUG-CAA-AAU-CCU-GCG Ala – Val – Pro – Val – Glu – Asp – Pro - Ala ATG-CGT-GGA-TAC-GTA-CAG-TGA-ACC-ACT UAC-GCA-CCU-AUG-CAU-GUC-ACU-UGG-UGA Tyr – Ala – Pro – Met – His – Val – Thr – Try – STOP

  45. More Time Trials TAC-GGC-AGT-ATG-GTG-CAC-TAG-ACC-ATT AUG-CCG-UCA-UAC-CAC-GUG-AUC-UGG-AUU START– Pro– Ser– Tyr– His– Val– Iso– Try – STOP TAC-CCG-ACT-ATG-TCG-ACA-GAT-TGG-ATT AUG-GGC-UGA-UAC-AGC-UGU-CUA-ACC-AUU START– Gly– STOP

  46. Reminder: Normal Hemoglobin Gene: TAC-GGA-CAT-ATA-GTA-CAA-ATC AUG-CCU-GUA-UAU-CAU-GUU-UAG MET-PRO-VAL-TYR-HIS-VAL-STOP

  47. Mutations • Any change in the sequence of DNA bases. • Changes in the DNA results in the change of the proteins. • The cell carefully proofreads the DNA to check for errors. • Every so often, error is missed which changes the protein. • Mutations are only passed to the offspring if they occur in the reproductive cells (egg and sperm).

  48. Chromosomal Mutations • A structural change in a chromosome that breaks and rejoins incorrectly. • The translocation of different genes to different chromosomes. • Many cancers http://upload.wikimedia.org/wikipedia/commons/c/cb/Translocation-4-20.png

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