Discovery of DNA

Question 1

What did Fredrick Griffith suggest

Answer 1

Fredrick Griffith’s experiment was one of the first experiments suggesting that bacteria are capable of transferring genetic information through transformation

Question 2

Fredrick Griffith’s experiment details

Answer 2

• Type R non virulent bacteria injected into mouse: no bacteria recovered, mouse stayed alive
• Type S virulent bacteria injected: virulent type S bacteria recovered, mouse dead
• Heat killed type S injected: No bacteria recovered, mouse alive
• Type R and Heat killed type S: virulent type S recovered, mouse dead
• Proves some transformation from heat killed S to non virulent R to make R virulent.

Question 3

What did the Avery-MacLead-McCarty experiment demonstrate

Answer 3

That DNA was the material causing bacterial transformation

Question 4

How did Avery & co prove this

Answer 4

• Heat killed virulent S strain mixed with enzymes that destroy specific substances (RNases, proteases, lipases etc)
• The mixture was added to cultures of R strain bacteria
• Cultures treated with all enzymes except DNase contain transformed S strain bacteria
• Proves that DNA was causing the transformation

Question 5

What did Hershey & Chase prove

Answer 5

They confirmed that DNA was genetic material using bacteriophage T2.

Question 6

What bacteria did Griffith use

Answer 6

Streptococcus pneumoniae (pneumococcus)

Question 7

In Griffiths experiment which strain of pneumococci was isolated from dead mice

Answer 7

Live smooth cells (virulant type S cells)

Question 8

What observations in Avery’s research showed that DNA is the transforming substance

Answer 8

• enzymes that degrade proteins did not prevent transformation
• RNase did not prevent transformation
• DNase, an enzyme that digests DNA did prevent transformation

Question 9

What did Hershey & Chases experiments depend on that distinguishes proteins from DNA

Answer 9

• Sulphur
• Phosphorous