Presentation on theme: "DNA as Genetic Material – Structure and Replication"— Presentation transcript:
1DNA as Genetic Material – Structure and Replication Chapter 16
2Warm-UpWorking with your table partner, write as many things as you can remember about DNA on your whiteboard!!Share!!Keep track on your whiteboard of your ideas that have already been shared so you don’t repeat what someone else has already said and our discussion isn’t redundant…
3Follow-UpOn your sticky note, take 1-2 minutes to write your name and any questions you have about DNA – at the end of class, we’ll see if your questions have been answered and if not we’ll address them over the next few weeks!If no questions come to mind right away, think about DNA technology and how
5With your table partners… You have pictures of the experiments/results of 4 key experiments in the development of determining that DNA is the genetic material1) Griffith 2) Avery, McCarty, & MacLeod3) Hershey & Chase 4) ChargaffFor each experiment…Briefly describe what occurred in the experiment (set-up and results)Determine what could be concluded about DNA from that experiment
11James Watson and Francis Crick Read the original paper that Watson and Crick reported presenting their model for DNA structureAs you read, underline/highlight the information that you recognize either from our discussion today or from your previous exposure to learning about DNA [the language will be challenging – focus on the facts!]Then, briefly describe what data helped them build their model and the key structural components/conclusions they identified
13Business Quest Quiz over structure/replication the MONDAY we get back! Due the Thursday we get backSome questions about scientists, structure, and replication… others about protein synthesisYou may get ahead over the break Quiz over structure/replication the MONDAY we get back!
15Proteins that DNA wraps around From DNA to ChromosomechromosomeA strand of human DNA is about 3 m long…How does it fit into all our cells??SupercoilingnucleuscellProteins that DNA wraps aroundhistonesNitrogenbasesDNA
16Details of DNA Structure Nucleotides are the monomers of nucleic acids5 carbon sugarRiboseDeoxyriboseNitrogen BaseAdenineThymineCytosineGuanineUracilPhosphate5’ Carbon5’4’1’2’3’3’ Hydroxyl
17Details of DNA Structure 5’ Carbon3’ HydroxylWhat do you notice about the 5’ and 3’ ends of the two strands?They’re ANTIPARALLEL!!Why? For the nucleotide bases to line up3’ Hydroxyl5’ Carbon
18Details of DNA Structure 5’ Carbon3’ HydroxylWhat holds the nucleotides together?3’ Hydroxyl5’ Carbon
19Details of DNA Structure Nucleotide Bases: Purines and PyrimidinesPURINES“Aggies are Pure” – A and G are Purines which have 2 ringsPYRIMIDINES“TCU Cheerleaders build Pyramids” – T, C, and U (in RNA) are Pyrimidines have one ring
20Details of DNA Structure 5’ Carbon3’ HydroxylWhat do you notice about the number of hydrogen bonds between the different bases?3’ Hydroxyl5’ Carbon
21CFUWhich letter represents the bonds that will be broken when a strand of DNA gets replicated?
22CFU What type of bonds are the bonds between the nucleotides? Covalent IonicVan der WaalsHydrogen
23CFUWhich letter represents the 3’ end of the DNA molecule?
26CFU Which base pairs are most likely easier to break and why? A-T because they are held together by 3 hydrogen bondsC-G because they are held together by 3 hydrogen bondsA-T because they are both purinesC-G because one is a purine and the other is a pyrimidine
36DNA Replication Coordinated by a large team of enzymes! helicases polymerasesligasesprimases
37DNA ReplicationProblem: Nucleotides can only be added to the 3’ end by DNA Polymerase III…Solution: OkazakiLeading and Lagging StrandsLeading StrandContinuous synthesisLagging StrandOkazaki fragmentsJoined by ligase
38Many little pieces of 5’ 3’ linked together later Remember: DNA polymerase can only add nucleotides to the 3’ end, so DNA gets built in the 5’ 3’ direction!3’5’Parental DNA5’Okazaki fragments3’DNA polymerase3’Ligase5’Leading and lagging have the same origin of replication, but since DNA polymerase can only add on the 3’ end, the lagging strand has to start backwards and make little pieces to link togetherLeading strandOne piece of 5’ 3’Lagging strandMany little pieces of 5’ 3’ linked together later
39Priming DNA SynthesisDNA polymerase can only extend an existing DNA molecule; it cannot start a new oneShort RNA primer is built first on parent DNA by primaseRNA primer later removed by DNA polymerase I
40Primase builds the RNA primer Replaces RNA nucleotides with DNA Priming DNA SynthesisCloser look…Primase builds the RNA primerReplaces RNA nucleotides with DNAPrimaseDNA polymerase
43Test your understanding… On some paper, write A – H and decide whether each letter represents the 3’ or 5’ end of DNA. Then, label the sections (A-B, C-D, etc) as “leading” or “lagging”A-B: LeadingC-D: LaggingBCAD5’3’3’5’3’5’EH3’5’GFF-E: LeadingH-G: Lagging
44Editing and Proofreading DNA Why do we not always get cancer?DNA can repair itself!!!Since DNA polymerase III does 1,000 base pairs/second, it makes a lot of errorsDNA Polymerase I (only 20 bp/sec) excises mismatched bases, repairs the DNA, and removes the primerDNA polymerase I reduces error from 1 in 10,000 bp to 1 in 100 million bp!!
45Problems at the end…Ends of chromosomes are “eroded” with each replication (don’t get fully copied)Telomeres are expendable, non-coding sequences at the ends of the DNA strandshort sequence of bases repeated 1000s of timesTTAGGG in humans
46Telomeres and AgingIn the absence of telomerase, the telomere will become shorter after each cell division. When it reaches a certain length, the cell may cease to divide and die.
47Putting it ALL together Summarize the roles of the key enzymesLabel the diagram showing the steps of DNA replicationDNA Structure – Questions and Practice
48Summary of Replication Enzymes FunctionHelicasePrimaseDNA Polymerase IDNA Polymerase IIILigaseUnzips DNA (breaks H-bonds between nucleotides)Builds RNA primer in leading strand and Okazaki fragmentsAdds DNA nucleotides (20 bp/s); replaces RNA primer with DNA; repairs errors in DNAAdds DNA nucleotides (1,000 bp/s)Joins Okazaki fragments (using phosphate groups)
49In the diagram below, label the key enzymes and structures in DNA replication. Be sure to label 3’ and 5’ ends, too!