Ch. 9 and 10: Famous Experiments and DNA synthesis

Question 1

What was the Griffith experiment about?

Answer 1

Two strains (R and S). Some kind of hereditary material was transferred between the two, causing the non-virulent strain to become virulent. This helped lay the groundwork for determining that DNA is the hereditary material

Question 2

What was the Avery experiment?

Answer 2

• -Each of the 3 macromolecule suspects (protein, RNA, and DNA) were each digested by an enzyme specific to that molecule. The only time transformation did not occur was when DNA was not present.
• -Follow-up to Griffith’s experiment, which showed that DNA was the heriditary material.

Question 3

What was Hershey-Chase experiment?

Answer 3

Many believed that there was a possibility that all of the protein had not been removed from the cells in the Avery experiment. Therefore, radiolabeled protein and DNA were used by viruses to infect cells. Only the DNA was found inside the host cell, whereas the protein was outside the cells.

Question 4

What was the Meselson-Stahl experiment?

Answer 4

• -Purpose: Determine the method of DNA replication.
• -Several generations of DNA were made in the presence of heavier nitrogen atoms (15N instead of 14N). Then lighter nitrogen atoms were added.
• -The DNA was found to replicate in a semi-conservative manner

Question 5

What does semi-conservative replication mean?

Answer 5

That with each successive generation one strand from the previous generation will remain (parent strand), while a new strand is formed to it (daughter strand).

Question 6

What does conservative replication mean?

Answer 6

Parent and daughter DNA strands remain separate through each successive generation

Question 7

What does dispersive replication mean?

Answer 7

Each successive generation will have a equal mixture of parent and daughter strand. This differs from the semi-conservative model, because in the Meselson-Stahl experiment two differently weighted bands were found. If DNA replication was dispersive only one intermediate band would be found

Question 8

What order do enzymes begin DNA synthesis?

Answer 8

• -Helicase opens the helix
• -DNA binding proteins prevent the separate strands from joining back together
• -Topoisomerase cuts and rejoins DNA strands to relieve torsional strain created by the opening of the double strand
• -Primase adds primers for DNA polymerase
• -DNA Polymerase 3 adds nucleotides

Question 9

What direction is the DNA strand always synthesized in?

Answer 9

The 5’–>3’ direction (bases are added to the 3’ end)

Question 10

What is the lagging strand?

Answer 10

The strand that is synthesized in the opposite direction (away from) the replication fork

Question 11

What are Okazaki fragments?

Answer 11

These are the sections of DNA created in the lagging strand that are later sealed up by DNA ligase

Question 12

What direction is mRNA read in order to make protein?

Answer 12

3’–>5’