2 What is DNA? Deoxyribonucleic acid DNA determines an organism’s traits DNA achieves control by producing proteinsRemember: proteins give us structural building material and allow function (enzymes)DNA is the information for life
3 Time Line – Early History of Genetics Key Players 1840’s Mendel Early 1900’s T.H. Morgan Griffith Avery Hersey and Chase Chargaff Early 1950’s Franklin and Wilkins Early 1950’s Pauling Watson and CrickPlace these names and dates on your timeline under “Scientists”
4 DNA is the genetic material Early 1900’s, the identification of the molecules of inheritance loomed as a major challenge to biologistsT. H. Morgan’s group showed that genes are located on chromosomes, the two components of chromosomes—DNA and protein—became candidates for the genetic material
5 Early History of Genetics The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928He worked with two strains of a bacterium, one pathogenic and one harmless. He did transformation experimentsBasically he found that harmless bacteria became deadly when they took in DNA from dead pathogenic bacteria
6 Fig. 16-2Mixture of heat-killed S cells and living R cellsEXPERIMENTLiving S cells (control)Living R cells (control)Heat-killed S cells (control)AveryHe separated the components of the bacteria and found only the DNA extract caused mice to dieRESULTSFigure 16.2 Can a genetic trait be transferred between different bacterial strains?Mouse diesMouse healthyMouse healthyMouse diesLiving S cells
7 Evidence That Viral DNA Can Program Cells More evidence for DNA as the genetic material came from studies of viruses that infect bacteriaSuch viruses, called bacteriophages (or phages), are widely used in molecular genetics research
8 Hersey and Chase Fig. 16-4-3 EXPERIMENT Empty protein shell Radioactivity (phage protein) in liquidRadioactive proteinPhageBacterial cellBatch 1: radioactive sulfur (35S)DNAPhage DNACentrifugeRadioactive DNAPellet (bacterial cells and contents)Figure 16.4 Is protein or DNA the genetic material of phage T2?Batch 2: radioactive phosphorus (32P)CentrifugeRadioactivity (phage DNA) in pelletPellet
9 Next Steps… What is DNA made of? It was known that DNA is a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate groupIn 1950, Erwin Chargaff reported that DNA composition varies from one species to the next, however that the nitrogen based are found in predictable ratios:A = T and C = G
10 Finding the Structure of DNA After most biologists became convinced that DNA was the genetic material, the challenge was to determine how its structure accounts for its roleMaurice Wilkins and Rosalind Franklin were using a technique called X-ray crystallography to study molecular structureFranklin produced a picture of the DNA molecule using this technique
11 The Discovery of DNA Watson and Crick – 1953 Double Helix – long twisted zipperSegment with James Watson
12 Structure of DNA DNA is a long molecule Composed of nucleotides Simple sugar – deoxyribosePhosphate groupNitrogen base – Adenine- Guanine- Cytosine- ThymineStructure of DNA
13 DNA Structure Cont.Animation on how DNA is packaged into the nucleus
14 A pairs with T C pairs with G S – A ..…T – S | | P P | | | |S – G ..…C – S| |P P| |S – C ..…G – SA pairs with TC pairs with GWeak Hydrogen Bond
15 DNA Instructions for life The sequence of nitrogen bases forms the genetic instructions for an organismA-T-T-G-A-Cis different thanT-T-C-A-A-GThey code for different proteins and therefore structure and function of an organism
16 How can we use DNA?Nucleotide sequences can be used to determine evolutionary relationshipsOrganisms that are closely related have similar DNAEx. Gorilla and Chimp – very similarGorilla and Rose Bush – very differentIt can be used to determine if two people are relatedDNA can be used to compare DNA from a crime scene to DNA from a suspect
17 Complementary Strands If one side of the DNA molecule consisted of the following nucleotide bases, what would the other side be?ATC CTG GAT TAT GAC CAT ATG
19 DNA ReplicationYou have learned that cells divide through the process of mitosis and meiosisIn order to do this, each cell has to make a copy of its DNADNA is copied through the process of DNA ReplicationWhat might happen DNA replication did not occur prior to cell division?
20 How DNA Replicates Remember: DNA is composed of two strands A pairs with TC pairs with GSo if you know the order of bases on one side, you know the order on the other side (the complementary strand)During replication, each strand serves as a pattern
21 *What has to happen first in to make a copy of the DNA? FigATCGTAATGC(a) Parent moleculeFigure 16.9 A model for DNA replication: the basic concept*What has to happen first in to make a copy of the DNA?
22 (b) Separation of strands FigATATCGCGTATAATATGCGC(a) Parent molecule(b) Separation of strandsFigure 16.9 A model for DNA replication: the basic conceptWhat type of molecule might help the two sides of the DNA molecule separate?
23 (b) Separation of strands FigATATATATCGCGCGCGTATATATAATATATATGCGCGCGC(a) Parent molecule(b) Separation of strands(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strandFigure 16.9 A model for DNA replication: the basic conceptWhat types of molecules might be used to addnucleotides and bind the sides together?
24 Enzymes involved in DNA Replication Helicase – unwinds the DNA strand to begin replication (it’s like unzipping a zipper)DNA Polymerase – adds nucleotides, one at a time to the open DNA strand (in humans up to 50 nucleotides per second)Ligase - joins the sugar-phosphate backbones of the newly formed strand. (it’s like gluing the sides together)
25 Steps of DNA Replication Step 1 – An enzyme breaks the H+ bonds between the nitrogen bases that holds the two strands together (un-zipping the molecule)Step 2 – Free floating nucleotides in the cell bond to the complementary bases on each of the original strandsStep 3 – An enzyme secures the two strands together, forming two new chains
26 DNA Replication Cont.DNA replication results in the formation of two identical strands from the one original DNA molecule.What do you think the word “semiconservative” means?
27 DNA Replication is Semiconservative Watson and Crick’s semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
29 Compare the two new strands of DNA. Are they the same or different? Why? GCGCGCGTATATATAATATATATGCGCGCGC(a) Parent molecule(b) Separation of strands(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strandFigure 16.9 A model for DNA replication: the basic concept
31 From DNA to ProteinThe sequence of nucleotides in DNA contains information that produces proteinsProteinsStructuresEnzymesBy controlling protein production, DNA controls cells
32 RNA Different from DNA in 3 ways RNA – single strand Sugar in RNA is ribose (DNA = deoxyribose)RNA has uricil (U) instead of thymine
33 The cell works like a factory DNA provides “workers” with instructions for making proteins“workers: bring over the parts (amino acids) to the assembly lineWorkers = RNA
34 3 Types of RNA Messenger RNA (mRNA) brings the info from the nucleus to the factory floor (cytoplasm)Ribosomal RNA (rRNA) – ribosomes are made of rRNAClamp onto mRNA and use its info to assemble amino acidsTransfer RNA (tRNA) – “supplier”Transports amino acids to the ribosomes where they are assembled into proteins
35 RNA Transcription Read steps in figure 11.6 (pg 296) Explain how it is different from DNA replicationAnimation of TranscriptionHHMI animation
36 The role of tRNAFor proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomesThis is the role of tRNA
37 tRNA Composed of about 80 nucleotides Each tRNA only recognizes only one amino acidThe amino acid bonds to the tRNALocated on the base of the tRNA molecule are three nitrogen bases, called an anticodon, that pair up with an mRNA codon during translation
38 tRNABasically, the tRNA molecule transfers the information for making proteins to the correct codon on the mRNA.If the mRNA has the codon for that particular amino acid, the tRNA binds, if it does not, the tRNA doesn’t bind and the amino acid that the tRNA is carrying is not made.
39 Amino Acids to Proteins Proteins are made in the RibosomesProteins are made of Amino AcidsAs multiple tRNA molecules attach to the mRNA, an enzyme joins the two amino acids by forming a peptide bond.
40 Translation of DNA to Protein Translation AnimationHHMI animation
41 The Genetic CodeA code is needed to convert the language of mRNA into the language of proteins amino acidsThere are 20 different amino acidmRNA only has 4 bases (AUCG)Ala: Alanine Cys: Cysteine Asp: Aspartic acid Glu: Glutamic acidPhe: Phenylalanine Gly: GlycineHis: Histidine Ile: Isoleucine Lys: LysineLeu: Leucine Met: MethionineAsn: AsparaginePro: ProlineGln: GlutamineArg: ArginineSer: SerineThr: ThreonineVal: ValineTrp: TryptophaneTyr: Tyrosisne
42 The Genetic Code Cont.Scientist found that a group of 3 nucleotides codes for 1 amino acidEach set of 3 nucleotides that code for an amino acid is called a codon
43 The Genetic Code Cont.Some codons don’t code for amino acids, they are instructions for assembling proteinsStop codon = UAAStart codon = AUG
44 Genetic Code Cont.All organisms use the same genetic code for assembling proteinsUAC = tyrosine in humans, birch trees, and bacteria
46 Critical Thinking Questions How specific are the tRNA molecules?How does energy play a role in all this hustle and bustle?How does translation begin and end?What happens to the mRNA strands?
47 Compare and contrast Transcription and Translation Where?What is used as a template?What is used to synthesize the new strand?What is the new strand made of?
48 Compare and Contrast Replication and Protein Synthesis Where?When?Purpose?Starting point?What enzyme is used to synthesize the new strand?Associated proteins?Nucleotides?Finishing Processes?Where does the finished “product” go?
49 Read the Help Wanted ad below Read the Help Wanted ad below. Based on your notes, tell me “who” is qualified to fill each position. Your choices are DNA, tRNA, and mRNA. Help Wanted!Positions Available in the genetics industry. Hundreds of entry-level openings for tireless workers. No previous experience necessary. Must be able to transcribe code in a nuclear environment. The ability to work in close association with ribosomes is a must.Accuracy and Speed vital for this job in the field of translation. Applicants must demonstrate skills in transporting and positioning amino acids. Salary commensurate with experience.Executive Position available. Must be able to maintain genetic continuity through replication and control cellular activity by regulation of enzyme production. Limited number of openings. All benefits.Supervisor of production of proteins—all shifts. Must be able to follow exact directions from double-stranded template. Travel from nucleus to the cytoplasm is additional job benefit.
52 Mutations: Changes in DNA Mutation – any change in the DNA sequence that also changes the protein it codes forMutations can happen in reproductive cells and in body cells (cancer)
53 Point Mutation A change in a single base pair in DNA Look at this simple analogyTHE DOG BIT THE CATTHE DOG BIT THE CAR
54 Frameshift MutationWhen a single base is added or deleted from a DNA strandIt shifts the reading of the codons by one base
55 More about MutationsLook at table 12.3 on pg Gather some information about the different types of mutations. Look at the examples of the diseases associated with each type of mutationRead pg 349.-What are the results of mutations to body cells?-What are the results of mutations to sex cells? -Why is a mutation in a sex cell considered potentially more harmful than one in a body cell?
56 Chromosomal Mutations Changes that occur at the level of the chromosomesOccurs when parts are broken off and lost during mitosis or meiosisFew chromosome mutations are passed on to the next generation because the zygote usually dies or is sterileVideo Clip