Objectives for Exam 3 PCB 3063 Summer 2012 Structure and Chemical Properties Chapter 9 This section covers the history of the discovery that DNA is the genetic material the chemical structure of DNA and how its biological properties arise from its chemical and physical properties The main thing here is to know the basic structure of DNA and how the base sequence of a particular DNA molecule i e its G C affects its physical and chemical properties Q Be able to describe and interpret the experiments on the transformation of Streptococcus which showed that DNA is the genetic material in bacteria Experiments by Griffith with steptococcus pneumoniae on mice showed some sort of transforming factor in the living virus converted the killed virus Then Avery demonstrated the transformation from Rough to Smooth is due to DNA in the heat killed smooth cells EX tobacco mosaic virus uses RNA as their genetic material Q Know that all cells and organisms use DNA as the genetic material but that some viruses use DNA and some use RNA as their genetic material Q Know the difference between nucleic acid bases nucleosides and nucleotides ribose and deoxyribose and where on ribose deoxyribose the phosphate and phosphodiester bonds are attached and where the nucleic acid base is attached Nucleic acid bases Nitrogenous base o 2 types Pyrimidines C T U o 6 member single ring o cytosine thymine and uracil Purines A G o 9 member double ring o adenine and guanine Pentose sugar 5 carbon ring o Pentose is found in nucleic acids This gives them their name Ribonucleic acids RNA containing ribose Deoxyribosenucleic acids DNA has a Hyodrogen atom instead of a Hydroxyl group on the 2nd Carbon DE oxy Takes away the Oxygen atom Phosphate group o Phospodiester bond 3 5 bond produces a dinucleotide nucleoside purine pyrimidine base and a ribose or deoxyribose sugar nucleotide nucleoside phosphate Q Be able to draw a piece of DNA or RNA showing the structure of ribose or deoxyribose the phosphodiester bonds the placement of the base on the sugar and the 5 and 3 ends of the molecule See above pictures or pg 191 fig 9 7 9 8 pg 192 fig 9 10 Q Know by name which bases are purines and which are pyrimidines Purines Adenine Guanine Pyrimidines Cytosine Thymine and Uracil Q Know the differences between DNA and RNA in terms of chemical composition and physical structure Sugar ribose in RNA instead of deoxyribose Ribose makes RNA chemically less stable Nitrogenous base uracil replaces thymine Uracil provides a tag for distinguishing RNA from DNA Most RNA is single stranded but can form double strand by pairing with itself Complex secondary structures are possible o tRNA rRNA mRNA DNA double helix held together by complementary base pairing A T 2 H bonds G C 3 H bonds Physical chemical properties of DNA depend on its G C Know that RNA is chemically unstable spontaneously degrades into free nucleotides fairly rapidly because of the 2 0H on ribose whereas DNA is chemically quite stable Q Be able to describe the Watson and Crick model for the double stranded helix model of DNA structure Antiparallel double helix in which the two strands are held together by complementary base pairing of A with T and G with C in the center of the molecule and the phosphate backbone is directed outward Because A on one strand pairs with T on the other strand G with C the base sequence of the two strands are complementary Q Understand how the density and Tm of DNA is affected by its base composition G C and why G C pairs are held together by 3 H bonds whereas A T pairs are held together by only 2 H bonds therefore G C pairs are more stable stronger bond than A T pairs Density of DNA depends on its C G G C has 3 H bonds while A T Melting temperature increases with increased G C because they are only has 2 more strongly bound together they are harder to denature the bonds are more difficult to break apart DENSITY OF DNA DEPENDS ON ITS G C Q Know that heating a solution of DNA leads to denaturation making DNA single stranded and be able to define the term Tm Tm temperature at which DNA is 50 melted o More GC stronger the molecules are held together and the more energy it takes to separate Understand that the density of a DNA molecule can be measured by centrifugation and that Tm can be measured by heating a DNA sample while measuring its absorbance of UV light Q Know what DNA renaturation is and be able to describe how DNA hybridization experiments are done and what they are used for DNA renaturation lowering the temp of a sample of denatured DNA allows the base to reform Hybridization can be done with DNA in solution on filters or on chromosomes Because of complementary base pairing the base sequence of different DNA molecules also provides us with a way to detect specific DNA sequences in a complex mixture of DNA molecules by renaturation this is also called hybridization In a DNA hybridization experiment DNA samples from two different sources is denatured mixed together and allowed to renature If the two DNA samples contain DNA segments with similar sequences then some duplex DNA molecules will be formed in which one of the two strands of a double stranded molecule of DNA comes from the two different sources different organisms DNA Replication Chapter 10 Complementary base pairing underlies DNA replication In this section the historical evidence that DNA replication is semiconversative is presented and the enzymology of DNA replication is described Some important differences between DNA replication between prokaryotes and eukaryotes are introduced Q Be able to describe and interpret the results of the Meselson Stahl experiment which showed that DNA replication is semiconservative Be able to diagram the results of their experiment and what they would have obtained had replication proved to be conservative or dispersive Meselson Stahl took E coli labeled with 15N and added it to 14N medium o over several generations the density bands showed that replication and allowed it to replicate must have consisted of one old strand and one new strand For more details see pg 206 in the text Q Know the requirements of DNA polymerase template primer direction of synthesis what nucleotides are used and the reaction by which it makes DNA Formation of a phosphodiester bond involving the phosphate group on one nucleotide and the 3 OH on ribose deoxyribose on the other nucleotide adds dNTPs to the 3 end of DNA 5 to 3 synthesis equires a DNA template requires a primer
View Full Document
Unlocking...