DNA - The genetic material Flashcards

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1
Q

Who discovered DNA and how?

A

Friedrich Miescher in 1869
- Isolated nuclei from leukocytes (from pus on bandages)
- Broke cells open with detergent, treated with acid to form a pp of ‘nuclein’

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2
Q

Altmann’s contributions

A

The name changed to nucleic acid
- Also found purine and pyrimidines

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3
Q

Miescher’s chemical analysis

A

Chemical analysis - found nuclein was made of phosphorus , carbon, oxygen etc
=> also found when a cell divides it doubled

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4
Q

Issues with Miescher’s experimental procedure

A
  • Determined egg and sperm had diff amounts of N
  • Concluded nuclein was not genetic material as a result
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5
Q

Griffith’s Experiment (1928) - Transforming non-lethal strain of Streptococcus pneumoniae to lethal

A
  • S strain live cells (pathogenic) killed mice while R strain did no harm
  • When S strain was heat-killed, mouse lived
  • When heat-killed S was injected with R, mouse lived and S strain live cells were found
  • The extract of S strain transformed R strain (transforming principle) to be pathogenic do to the DNA passing on the genes for such
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6
Q

Avery, Macleod & McCarty showing DNA is the transforming factor (1944)

A
  • Combined S strain extract w/ R strain with:
  • no components destroyed like Griffith = live S strain recovered
  • Polysaccharides, lipids, RNA destroyed by enzymes = strain recovered
  • Protein destroyed = strain survived (surprising as was thought to be genetic material)
  • DNA destroyed = no live S strain + only cond. mouse lives

Showed DNA is genetic material

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7
Q

Acceptance of DNA being genetic material

A
  • Avery, Macleod & McCarty was ignored by scientists (esp. those looking into what was the genetic material) at the time
  • Hershey and Chase confirmed their findings in 1952 => and this was when scientists accepted it
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8
Q

Evidence that DNA is the genetic material in phage: the Hershey–Chase experiment (1952)

A
  • Used radioisotopes to give DNA + protein labels that could be tracked during infection
  • Phosphorus (32^P) into DNA + Sulfur (35^S) into proteins of separate phage cultures
  • Infected E.coli cultures , sheared empty phage ‘bodies’ off bac. cells with blender
  • Separated cells from phage bodies in centrifuge + measures radioactivity in solid bacteria + liquid phage ghosts
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9
Q

Results from Hershey-Chase Experiment (1952)

A
  • When 32^P phages infected E.coli, radioactivity was inside bac. cells - DNA entered cells
  • When 35^S phages were used, radioactivity was in phage ghosts - protein did not enter the cell
  • Also, progeny of 32^P phages remained labeled, while 35^S phages didn’t

All indicates DNA is hereditary material

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