DNA as genetic material 1

- carried on chromosomes 

- linked closely- unless they are distant on loci 

Griffith (1929) s.pneumoniae is lethal in mice

2 strands= smooth and rough 

smooth -> wild type and lethal 

rough -> mutant and non lethal 

smooth bacteria killed by boiling and injecting into the mice = mice survived 

-> BUT inject R and dead S cells = mice die as R turned into S = transformation 

what caused it to transform? 

DNA tranforming principle 

detergent to lyse heated S 

- removed proteins and combined with R= mice die 

- removed RNA and combined with R= mice die 

- removed DNA and combined with R= mice live 

- DNA = high P 

- protein= high S 

T2 put on bacteria when radioactive 32P= therefore DNA molecule of inheritance 

T 

C 

U 

A

G 

D-ribose 

unstable to due to extra -OH 

2-deoxyribose 

ribose or deoxyribose linked to purine or pyridamine 

- A + ribose= adenosine 

- U + ribose= uridine 

- G + 2-deoxyribose = deoxyguanosine 

- C + deoxyribose = deoxycitidine 

- phosphoric acid ester of a nuceloside 

- ribsonucleosides have 3 free -OH groups of sugar ring- 3-ribonuceoside monophosphates are possible 

pyridamine has to eqaul purine 

- 5' and 3' structure- designed to detect where C atoms are 

watson and crick (1953) using x-ray 

B-DNA- H bonds between bases -> antiparrallel in sugar ring as distinct strands from bases 

- proteins make it easy to fix by detector 

- higher the G-C= higher density 

- typical mRNA is about 1.5 Kb long 

- dyes and antibiotics have stronger binding specificities for G-C or A-T 

- H bonds effected by temp or pH 

- dsDNA collapses into **DNA and is called helix-coil tranisiton 

- the temp at which ds-> ** is called the Tm 

- hyperchromic effect causes materials to decrease in their ability to absorb light 

- nature of DNA: homogeneous DNA melts at a lower temo range then heterogeneous 

- helix-coil transition changes denisty of DNA= ssDNA has a higher density of G-C than dsDNA 

- DNA denaturation and Cot value analysis 

- when ssDNA is returned to physiological conditions is may reassociate to for a double helix 

- however renaturation rates and completion mare affected by several parameters 

- semi conservative 

- meselson and stahl 

- E.Coli in medium with heavy nitorgen 15N not light N 

- then shifted the cultures into normal medium and isolated samples after 1-2 division cycles 

- prolonged centrifugation of CsCl a density gradient with the highest ion conc at the bottom of the tube 

- dneisty DNA is typically a funciton of GC/AT base composition but addition of 15N increases density of DNA relative to that with 14N 

and intermediate density bamd was formed between heavy and light band of the E.Coli 

E.coli do not undergo meiosis 

Taylor tested this with 3H thymidine labelling in grasshopper testes followed by slide-mounting and autoradiogrpahy 

harlequin chromosomes 

Phage Y genome has a linear 50Kb genome which can be readily be sheared by pipetting breaking the genome approx in the middle of the molecule giving fragments that differ in their GC content and then density= separation 

- KAISER introduced the wild type halves of this DNA into different bacteria culters simulataneously with infection with phage Y mutant for the same genes 

- then introduced lytic replicaiton by Y and recovered phage that were wild type for the markers on each hand of the genome