Lecture 11: DNA, the chemical nature of the gene

Question 1

Albet Kossel did what

Answer 1

isolated and named 5 nitrogenous bases

Question 2

Levene discovered what and proposed what based off his findings

Answer 2

Discovered that DNA consists of a large number of linked repeating units = nucleotides

Proposed tetranucleotide theory

Question 3

What is the tetranucleotide theory

Answer 3

theory that DNA consists of series of 4 nucleotide units containing all 4 bases in fixed sequence, this would mean DNA is NOT the genetic material

Question 4

Chargaff discovered what

Answer 4

different species vary in base composition but the compositions of A = T and G = C

Question 5

Griffith discovered what

Answer 5

that DNA was the source of genetic material

Question 6

Describe Griffiths experiment

Answer 6

Used Smooth (virulent) and Rough (nonvirulent) bacterial strains
- S killed mice
- R did not kill mice
- Heat killed S did not kill mice
- Heat killed S and live R killed mice
Proves transformation of genetic material

Question 7

What did oswald avery do

Answer 7

isolated the transforming substance as being DNA

Question 8

Describe avery’s experiment

Answer 8

• heat killed virulent bacteria
• Treat samples with protease, RNase, or DNase
• add samples to R type bacteria
• Only samples treated with DNase stayed nonvirulent proving that DNA is transformative agent

Question 9

What did Hershey and Chase prove

Answer 9

that DNA carried the genetic material of phages that infects bacteria

Question 10

Describe the Hershey and Chase experiments

Answer 10

• Used T2 phage either tagged with radioactive P or S
• P stuck to DNA and S stuck to protein coat
• Infected bacteria with phage
• blended bacteria to remove phage from outside of bacteria
• Centrifuged the experiment and found radioactive P in the pellet which means DNA went from phage into bacteria not protein
• S radiolable found in supernate

Question 11

Primary structure of DNA

Answer 11

Nucleotides held together by phosphodiester bonds

Question 12

Secondary structure of DNA

Answer 12

Nucleotides connected via covelent bonds

Question 13

What is polarity determined by

Answer 13

terminal phosphate group = 5’ head

Question 14

What strand serves as the DNA template for replication

Answer 14

Either strand can serve

Question 15

What were the three models proposed for replication

Answer 15

Conservative, semiconservative, dispersive

Question 16

Describe the conservative theory of DNA replication

Answer 16

Original DNA helix serves as template for new double helix

Question 17

Describe the semiconservative theory of DNA replication

Answer 17

Each strand of the original DNA strand serves as template for two new stands

Question 18

Describe the dispersive model of DNA replication

Answer 18

every round of replication results in hybrids of DNA double helixes that are part new and part old

Question 19

What did Meselson and Stahl prove

Answer 19

the semiconservative model of DNA replication

Question 20

Describe briefly the methods of Meselson and Stahl which proved semiconservative method

Answer 20

Used N14 nd N15 to distinguish new and old DNA

Grew a colony