WEEK 3 TOPIC 1 DNA encodes the genetic information that directs the cell how to make proteins and RNAs The information carried in the nucleotide sequence of our genes is first copied into an RNA intermediate TRANSCRIPTION The nucleotide sequence information in the RNA is then used to build proteins TRANSLATION The flow of genetic information from DNA to RNA to Protein is referred to as the Central Dogma of Molecular Biology Discovering the function of DNA By 1940s hereditary material known to reside on one or more chromosomes Chromosomes are composed of chromatin which is a complex of DNA and protein We knew proteins were made of 20 amino acids and DNA was made of 4 nucleotides 1 The flow of information from DNA into RNA is a process called transcription The flow of information from RNA into ultimately a protein being synthesized is called translation 2 DNA complexed with protein equals chromatin Briefly describe in your own words why it was initially assumed that protein was the hereditary component of chromatin It s assumed that protein was the hereditary component of chromatin because we know that having a surplus of different building blocks would make the diversity on the planet much bigger So when we were looking at DNA which has 4 different building blocks and protein which has 20 we assumed that protein had to be the deciding factor considering it was able to make many more unique sequences Discovery of the Structure of DNA Chargaff s Rules 1949 Amount of each dNTP varies between organisms but dA dT and dC dG in ALL organisms For every purine in double stranded DNA there appears to be a pyrimidine and specifically for every adenine there appears to be a thymine and for every guanine there appears to be a cytosine Rosalind Franklin and Maurice Wilkins X ray diffraction suggested helix of uniform width with stacked bases with sugar phosphate on outside photograph 51 bases were stacked on the inside of that helix and the sugars and phosphates were on the outside of that helix overall width of the DNA helical molecule is consistent James Watson and Francis Crick Only model that worked with the data is a double helix width of a DNA molecule is 20 angstroms Won Nobel peace prize Have two grooves larger one is called the major groove and the smaller one is called the minor groove The major groove gives you more room for a protein DNA Stabilizing Forces What forces hold the nucleotides together hydrogen bonds forming between a purine on one strand and a pyrimidine on the other Explains uniform width Explains Chargaff s rules Only when you put a purine opposite a pyrimidine do you get double helical molecules that have a 20 angstrom or two nanometer diameter Only G can fit opposite C and A opposite T in order for groups to be precisely positioned for H bonds to form between them one of them has to be upside down relative to the other one antiparallel One end of a nucleic acid molecule the end with an available phosphate group attached to the five prime carbon The three prime end of a DNA molecule is the end with an available hydroxyl group at its three prime carbon Any two molecules of nucleic acid that are complementary and antiparallel will spontaneously form these noncovalent hydrogen bonds and will form double stranded nucleic acid DNA Denaturation Separation of double helix into single strands accomplished by disrupting stabilizing forces 1 H bonds between opposite base pairs 2 Base stacking interactions o Planar organic rings are hydrophobic o o They stack to minimize contact with water Single strands of nucleic acid will come together into dsDNA if denaturing agent is removed as long as the bases are complementary and anti parallel nitrogenous bases are perpendicular to the sugar phosphate backbone and they don t want to be exposed to water so they stack together tightly to minimize their contact with water annealing renaturing If you have an aqueous solution of one million identical DNA molecules the melting temperature is the temperature at which all one million of them are 50 percent unwound Half of each of those molecules is unwound and half of each of those molecules is still holding on GC base pair has three hydrogen bonds holding it together and an AT base pair has two hydrogen bonds holding it together So the higher the GC content of a population of identical DNA molecules the higher its melting temperature will be The melting temperature is higher with identical DNA molecules if they re in the presence of positively charged ions Book Notes for Topic 1 Griffith finds that bacterial cells can be transformed o He performed experiments with mice to show that mice infected with the nonvirulent R form had no effect so a polysaccharide coat is necessary for virulence o If the S form is heated first it doesn t kill the mouse o A mixture of dead S form and R form killed the mouse which indicated that the dead virus transferred genetic information to the non virus transforming them from nonvirulent to virulent Avery MacLeod and McCarty identify the transforming principle o Removed all the protein from the S form and still found that the genetic information was passed to the R form o Solidified that the genetic material in bacteria at least is DNA Hershey and Chase demonstrate that phage genetic material is DNA o Viruses that infect bacteria bacteriophages or phages o Used P isotope to label DNA and S isotope to label proteins specifically o Deduced that DNA not protein consisted genetic material DNA Structure Fredrick Miescher discovered DNA in 1869 only four years after Mendels work o He extracted white substance from the nuclei of human cells and fish sperm and found different ratios so concluded that that was nucleic acid DNA s components were known but it s 3D structure was a mystery o Knew that it contained a five carbon sugar a phosphate group and a nitrogenous base either purine or pyrimidine o Phosphate group is attached to the 5 prime of the sugar and the base it attached the 1 prime and in addition an OH group is attached to 3 prime o Phosphodiester bond nucleotides dehydration linkages Chargaff Franklin and Wilkins obtained structural evidence o Chargaff Proportion of A T and proportion of G C o Franklin proved that DNA formed a helix o The two strands of the double helix are made up of long polymers of nucleotides it is known as the phosphodiester backbone of the molecule o Base pairs hold together the strands o G C have 3 hydrogen bonds and A T only have 2 o