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Transcript
DNA, RNA and Protein Synthesis Bell work 1. Which number is the Nucleus? 2. Which number are the ribosomes? 3. The endoplasmic reticulum? 4. What is the function of each? 5. Where is the DNA located? 1. 9 2. 4 3. 5/10 4. Nucleus stores DNA “brain” of the cell Ribosomes aid in making proteins ER aids in making proteins 5. In the nucleus Discovery of DNA Objectives 1. Describe the methods and experiments that were used by scientists in their search for the hereditary molecule. 2. How did scientific experiments lead the conclusion that DNA and NOT protein is the hereditary molecule. Griffith’s Experiments • Griffith was studying the bacteria that caused pneumonia to find out how it made people sick. – He was also trying to come up with a vaccine against the VIRULENT strain of the bacteria. – S type bacteria are protected from our bodies’ immune system by a sugar that surrounds them – R Type are not Griffith Explained • First he did what we call a control for his experiment – he injected one group of mice with one type of bacteria and another group with the other to see what would happen. – The group injected with the R type lived. – The group injected with the S type died. Griffith Continued • Next he killed the S type bacteria by heating it up to 60 degrees centigrade – This is hot enough to change the shape of proteins but not hot enough to do the same to DNA! • When the shape of the protein is changed it will not function the same way!!! • After he killed the S type bacteria he injected it into a third group of mice – They lived Griffith Continued • Finally in a fourth test he mix the heat killed (h-k) S type and the normal R type and injected the mixture in to a fourth group of mice. – They died. Griffith Conclusion • Griffith figured that when he killed the S type whatever causes characteristics to be passed from parent to offspring was still alive and got into the R type bacteria • Because this was not parent to offspring delivery of this information we call it TRANSFORMATION – Latin: trans – to cross; forma – a form; Transforma – to change form • The hereditary molecule was now outside the h-k S type bacteria and made its way into the R type bacteria which allowed the R type to transform into the S type bacteria! Griffith’s Experiment Avery’s Experiments • 1940’s America – Wanted to find out if it was DNA, RNA or protein that caused Griffith’s transformation – Used three different enzymes to destroy these molecules in three different batches of h-k S type bacteria • Group 1: H-k S type w/ Protease (destroys protein) • Group 2: H-k S type w/ RNase (destroys RNA) • Group 3: H-k S type w/ DNase (destroys DNA) – Then mixed the heat killed S types with the normal R type and injected three different groups of mice • Group 1 and 2 died Group 3 lived Avery’s Conclusion • The groups with the destroyed protein and RNA were still able to pass on hereditary information that caused the mice to die • The group with the destroyed DNA did not kill the mice • So it MUST be the DNA that is the hereditary molecule. Hershey-Chase Experiment • 1952 America – Martha Chase and Alfred Hershey wanted to confirm that DNA was the hereditary molecule • Used bacteria and bacteriophages (phages) • Group 1: radioactive phosphorus used to identify DNA injected into phages • Group 2: radioactive sulfur used to identify protein injected into phages • Each group was allowed to infect a group of bacteria Hershey-Chase Conclusion • When the bacteria was examined after the infection, it was found that ALL of the viral DNA and only a little protein made it into the bacteria QUIZ 1. Griffith’s experiment with pneumonia bacteria in mice showed that harmless bacteria could turn virulent when mixed with h-k bacteria that cause disease. True or False? 2. Avery’s experiments clearly demonstrated that the genetic material is composed of DNA. True or False? 3. The experiments of Hershey and Chase cast doubt on whether DNA was the hereditary material. True or False? They confirmed that DNA was hereditary material in viruses DNA STRUCTURE Objectives 1. Describe the discovery of DNA’s double helix structure. 2. Describe the structure of DNA and nucleotides. 3. Explain base pairing. DNA Double Helix • By the 1950’s it was accepted that DNA was the hereditary molecule but we still didn’t know what it looked like or how it worked DNA Double Helix • 1953 American James Watson and Englishman Francis Crick complete their work on the structure of DNA – For years they came close but couldn’t quite get the right structure without convincing Maurice Wilkins to steal Rosalind Franklin’s X-rays to give to them. – They concluded that the structure was a double helix which also help explained how the molecule could replicate itself. – In 1962 Watson, Crick and Wilkins won the Nobel Prize in Physiology or Medicine. DNA Nucleotides • DNA is made of repeating sub units called NUCLEOTIDES. • Each NUCLEOTIDE has three parts – Deoxyribose (five carbon sugar; yellow part of our model) – Phosphate group (white part of our model) • Phosphorus and oxygen covalently bonded together – Nitrogenous base (blue, orange, red and green parts of our model) • Made of nitrogen and carbon atoms DNA: How it’s held together • Deoxyribose and phosphate alternate on the sides – These are held together by a covalent bond • The Nitrogenous bases (bases) face the center and join the two strands in the middle – They are held together by hydrogen bonds Nitrogenous Bases • Four different kinds – Adenine (A) – Thymine (T) – Guanine (G) – Cytosine (C) • If they have a double ring they are PURINES (A and G) • If they have a single ring they are PYRIMIDINES (T and C) Complementary Bases • 1949 American Erwin Chargaff – Observed that in a many different organisms the amount of Adenine matched the amount of Thymine and that the amount of Cytosine matched the amount of Guanine • This gave us the BASE-PAIRING RULES and helped us even more understand what DNA looked like. • One complementary base pair contains one purine and one pyrimidine (A-T, G-C) • If one strand of DNA is GATTACA then the other is CTAATGT Complementary Bases • Bases are held together by hydrogen bonds which are not very strong this allows for the DNA to split and one side of the DNA to act as a template for creating a new complementary strand. DNA Models • We have many different ways to model the structure of DNA – One you have been staring at during this entire power point! – Another you made and is hanging from the ceiling! – A third is just using the letters of the base pairs: ATTCTC TAAGAG Quiz 1. What does the abbreviation DNA stand for? 2. Distinguish between purines and pyrimidines. 3. What was the significance of Franklin and Wilkins’s X-ray diffraction photographs regarding DNA structure? Answers 1. DNA = deoxyribonucleic acid 2. Purines are nitrogenous bases made of two rings of carbon and nitrogen atoms; Pyrimidines are nitrogenous bases made of a single ring of carbon and nitrogen atoms. 3. Their photographs suggested that the DNA molecule resembled a tightly coiled helix and was composed of two or three chains of nucleotides. DNA Replication Objectives: 1. Describe the steps in DNA replication 2. Describe the differences between prokaryotic and eukaryotic DNA replication 3. Explain the accuracy of replication and how errors are corrected. 4. Relate mistakes in DNA replication to cancer How DNA Replication Occurs Before we get started you need to know this: anything that ends in –ase is an enzyme, used to either break something apart or put something together 1. HELICASE brakes the hydrogen bonds holding the base pairs together creating a “Y” shape to the DNA, this is called a REPLICATION FORK How DNA Replication Occurs 2. DNA polymerases add complementary nucleotides to each of the original strands 3. The DNA polymerases release from the DNA and two new and identical strands of DNA are left ready for cell division • In each new double helix there is one original strand and one new one – SEMICONSERVATIVE REPLICATION Action at the Replication Fork • Replication happens in opposite directions for each strand – One side of the DNA will be copied and follow the direction of the replication fork – The other strand will be pieced together and seemed by an enzyme called DNA ligase Prokaryotic vs Eukaryotic Replication • Recall the shape of prokaryotic DNA and that of eukaryotic DNA • In prokaryotes there are ONLY TWO replication forks and they move in opposite directions until they meet Prokaryotic vs Eukaryotic Replication • In eukaryotes DNA polymerase adds new nucleotides at 50/second – if there were only two spots where nucleotides were being added it would take 53 days for our DNA to copy!!! – Replication begins at thousands of locations on a eukaryotic DNA molecule DNA Errors in Replication • Errors occur once for every BILLION paired nucleotides! – This is AMAZINGLY ACCURATE!!! • DNA polymerase not only adds nucleotides to the growing strand it ALSO proofreads for errors! • When an error does happen we call this a MUTATION – This has potential to change or harm the cell’s function DNA Errors in Replication • Some errors do not get fixed some can be caused by UV light or chemicals • Some mutations can lead to cancer DNA Replication and Cancer • If DNA is not replicated correctly a number of things can happen 1. Nothing at all 2. A mutation that allows the organism to survive and reproduce better • This mutation will usually become more common in a population 3. The mutation could be harmful • One type of harmful mutation is cancer. If the genes for controlling replication are changed a cell could begin to reproduce uncontrollably, creating a tumor Quiz 1. How is the exact replication of DNA ensured? By complementary base pairing and “proofreading” by DNA polymerase 2. What are replication forks? Areas of DNA where the double helix separates prior to replication Assignment • Illustrate DNA replication in six steps – You must label each drawing • Step one – strand of DNA before replication • Step two – helicase attaches and unwinds DNA (show replication fork!) • Step three – polymerase attaches • Step four – polymerase adds nucleotides (don’t forget one strand get added normally and the other gets added backwards. • Step five – show ligase mending backwards added strand • Step six – show semi-conservative replication of strands Protein Synthesis Objectives: 1. Describe how DNA contains the instructions for the building of proteins 2. Describe the function and three forms of RNA 3. Describe how proteins are transcribed 4. Describe the role of each form of RNA in the steps of translation 5. Describe the importance of studying the genetic code