Lecture 1 DNA Structure Flashcards
Transforming principle
Griffith found that dead virulent bacteria can transform to live form in the presence of a non-virulent live strain. Live IIS dead mouse, live IIR live mouse, dead IIS live mouse, live IIR dead IIS dead mouse. The substance that is transformed Griffith named the transforming principle - paved the way for Macleod and McCarthy
Proving DNA is genetic material
Macleod and McCarthy added heat killed virulent (IIS) bacteria to live non virulent (IIR) bacteria. If RNAse or Protease are added bacteria is still transformed non to vir. But if DNAse added IIR not converted proving DNA is genetic material. A process of elimination uses mice as in Griffiths experiment
X ray diffraction
Provides info on DNA structure. X-rays source > lead screen then crystal of substance bombarded w/xrays that diffract (bounce off it). Spacing of atoms in crystal determine diffraction pattern as dots on photographic film plate. (aka detector) providing diffraction pattern
Nitrogenous bases
Purine 2 ring A and G. Pyimidine 1 ring C T U. A-T or U 2 bonds whereas C-G 3 bonds. Hence CG favoured for regions not to be opened and AT favoured for coding regions that need to be opened.
Nucleosides
Nucleotides w/out a monophosphate group - so just base and sugar group - encode transmit and express genome. Nucleotides used as building blocks.
Phosphodiester bond
Condensation reaction, 5’ 3’ bond forming a diphosphate group + H2O as byproduct. Hydroxyl group on C3 bonds to phosphate group on C5 of other nucleotide.
DNA written 5’3’
5’ phosphorus available at right end and 3’ sugar available left. Only top strand needs to be written as bottom is complementary
Genetic material must
Contain complex info/ replicate faithfully/ encode phenotype/ have capacity to variate
Faithful/variable contradict - allows evolution not all variation beneficial
Genotype specifies RNA transcript
Determining proteins produced which are expressed in phenotype
Base pairs stacked flat
Like a spiral staircase. Maximising Van Der Waals/ hydrostatic force up down and H bonds left right.base pairs internal to helix protected from water
A B and Z form and grooves DNA
A compressed B relaxed both right facing. Z left facing helix. Major groove space to accommodate proteins and enzymes that bind DNA to do diff jobs eg replication
When proteins bind to DNA
They can bend it allowing DNA to open up so enzymes can enter more easily eg for transcriptiom
Denaturation
Loss of secondary structure leading to ss DNA. Promoted by heat, extreme ph and H bond breaking agents e.g. conc. Urea solution. Heat denatures cooling usually allows rehybridisation
E. Chargaff 1955
Discovered quantity of T =A and C=G disproving tetranucleotide theory (that bases occur in groups of 4
