BSC2010 Final Exam New Material DNA RNA structure DNA replication and Repair Objectives List the major components of a nucleotide and describe how these monomers are linked to form a nucleic acid I A Nucleotide is composed of three parts 1 Nitrogen containing nitrogenous base 2 Five carbon sugar pentose 3 One or more phosphate groups Monomer a molecule that can be bonded to other identical molecules to create a polymer First To create a nucleotide you start with the nitrogenous base which contains one or two rings that have nitrogen atoms in them called a base because the nitrogen atoms will take up H from the solution You add sugar to the nitrogenous base note in DNA the sugar is deoxyribose In RNA the sugar is ribose The solution is now called a nucleoside which can be defined as a nitrogenous base sugar To fully construct the nucleotide you just add the phosphate group to the 5 carbon of the sugar Next To create a nucleic acid i e polynucleotide you must combine multiple nucleotides Nucleotides are joined by a phosphodiester linkage which is basically just a phosphate group that connects the sugar components of two adjacent nucleotides Distinguish between a pyrimidine and a purine Pyrimidine and purine are both considered families of nitrogenous bases I Pyrimidine A nitrogenous base with a six membered ring of carbon and nitrogen atoms Members of pyrimidine family 1 Cytosine C 2 Thymine T 3 Uracil U II Purine A nitrogenous base with a six membered ring fused to a five membered ring These are larger than pyrimidine bases Members of Purine family 1 Adenine A 2 Guanine G NOTE Adenine Guanine and cytosine are found in both DNA and RNA while thymine is found in just DNA and Uracil is only found in RNA Distinguish between ribose and deoxyribose I Deoxyribose The sugar found in DNA II Ribose The sugar found in RNA The difference between these two is that deoxyribose lacks an oxygen atom on the 2nd Carbon in the ring Distinguish between the 5 and 3 end of a nucleotide A prime is put after the numbers of sugar carbons to distinguish them from the carbons used for the ring atoms of the attached nitrogenous base I 5 end of a nucleotide This end of a nucleotide has a phosphate attached to it II 3 end of a nucleotide This end of a nucleotide has a hydroxyl group attached to it The polynucleotide works like a one way street going from 5 to 3 Summarize the experiments performed by Hershey and Chase that provided evidence that DNA is the hereditary material Alfred Hershey and Martha Chase experimented using radioactive sulfur and phosphorus to trace the fates of protein and DNA of T2 phages that infected bacterial cells They did these experiments to see which of these molecules entered the cells and program the cells to make more phages Protein contains sulfur so radioactive sulfur atoms were incorporated into the protein of the bacteriophage Also atoms of radioactive phosphorus were incorporated into the DNA and not the protein E coli cell samples were allowed to become infected by the protein labeled and the DNA labeled batches of T2 The two samples were then tested to see which molecule protein or DNA would be capable of reprogramming them They found that the phage DNA entered the host cell while the protein did not which therefore supports the claim that the DNA must be containing the genetic material of the cell Phages also known as bacteriophages are viruses that infect bacteria Describe the structure of DNA Explain the base pairing rule and describe its significance I Structure of DNA DNA consists of nucleotides which as stated above consist of a nitrogenous base A G C T the deoxyribose sugar and a phosphate group The phosphate group attaches to the deoxyribose of the next nucleotide which forms a backbone The polynucleotide has directionality from the 5 end to the 3 end II Base pairing rule 1 Adenine pairs with Thymine 2 Cytosine pairs with Guanine This rule is significant because Adenine and Guanine are purines which are larger than Cytosine and Thymine which are pyrimidines Therefore in order for DNA to have a uniform diameter a purine must be paired with a pyrimidine Explain how RNA differs from DNA 1 RNA is single stranded while DNA is double stranded double helix 2 RNA has the sugar ribose while DNA has the sugar deoxyribose 3 DNA has the base Thymine while RNA has the base Uracil Summarize the functions of nucleic acids I Nucleic acids make up the genetic information in living things Form both DNA and RNA Functions 1 Store and transfer genetic information 2 Synthesize new proteins Describe the semiconservative model of replication and the significance of the experiments of Meselson and Stahl I Semiconservative model of replication Developed by Watson and Crick One of three models that was used Describes process that DNA is replicated in all known cells This model predicts that when a double helix replicates the two daughter molecules will have one strand from the old parent molecule and one new strand that is made This is different from the Conservative model of replication which says that the two parent strands somehow come together after the replication process The third model Dispersive model states that all four strands of DNA following replication have a mixture of new and old DNA Meselson and Stahl did experiments with cultured E Coli containing nucleotide precursors labeled with nitrogen isotopes They took a heavy isotope of nitrogen and transferred the bacteria to a medium with lighter isotope of nitrogen and waited for it to replicate Once it replicated another sample was taken and DNA was extracted from the bacteria in the samples and then centrifuged to separate the DNA The results they found eliminated the conservative model immediately and refuted the dispersive model The results concluded that DNA replication is semiconservative Describe the process of DNA replication including the role of the origins of replication and replication forks I Origins of Replication II Replication Forks The particular site that replication of DNA begins at Short stretches of DNA having a specific sequence of nucleotides Y shaped region where the parental strands of DNA are being unwound Helicase enzymes that untwist the double helix at the replication forks separating the two strands and making them available to use as template strands So basically DNA replication begins at the origins of replication proteins attach to this site separating the two strands of DNA and opening a bubble
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