Quiz 5 (Ch. 11)

Question 1

Conservative model (DNA replication)

Answer 1

• According to this hypothesis, both strands of parental DNA remain together following DNA replication. In this model, the original arrangement of parental strands is completely conserved, while the two newly made daughter strands also remain together following replication.
• Note: This is a WRONG hypothesis!

Question 2

Semiconservative model (DNA replication)

Answer 2

• In this mechanism, the doublestranded DNA is half conserved following the replication process. In other words, the newly made double-stranded DNA contains one parental strand and one daughter strand.
• Note: This is the CORRECT hypothesis!

Question 3

Dispersive model (DNA replication)

Answer 3

• Proposes that segments of parental DNA and newly made DNA are interspersed in both strands following the replication process
• Note: This is a WRONG hypothesis!

Question 4

What were the names of the scientists who proved the semiconservative model of DNA replication?

Answer 4

Meselson and Stahl

Question 5

What does oriC stand for?

Answer 5

Origin of chromosomal replication

Question 6

How is DNA replication initiated in bacterial cells?

Answer 6

DNA replication is initiated by the binding of DnaA proteins to sequences within the origin known as DnaA box sequences. The DnaA box sequences serve as recognition sites for the binding of the DnaA proteins.

Question 7

What does DNA helicase / DnaB protein do?

Answer 7

It breaks the hydrogen bonds between the two strands, thereby generating two single strands. Two DNA helicases begin strand separation within the oriC region and continue to separate the DNA strands beyond the origin.

Question 8

What does topoisomerase / DNA gyrase do?

Answer 8

It travels in front of DNA helicase and alleviates positive supercoiling.

Question 9

What do single-stranded binding proteins (SSB proteins) do?

Answer 9

Binds to the single-stranded DNA and keeps the parental strands apart (keep them from coming back together during replication)

Question 10

What does DnaC protein do?

Answer 10

Aids DnaA in recruiting DNA helicase to the origin of replication

Question 11

What does primase do?

Answer 11

It creates an RNA primer for polymerase III to begin replication at

Question 12

What does DNA polymerase III do?

Answer 12

Synthesizes the daughter strand of DNA for both the leading and lagging strands (ALWAYS in the 5’ -> 3’ direction!)

Question 13

What does DNA polymerase I do?

Answer 13

It excises the RNA primers places by primase and replaces these with DNA

Question 14

What does DNA ligase do?

Answer 14

It covalently links the Okazaki fragments together

Question 15

On which strand (5’ -> 3’ OR 3’ -> 5’) do Okazaki fragments occur?

Answer 15

They occur on the 3’ -> 5’ strand (the lagging strand) because the new DNA MUST be synthesized in a 5’ -> 3’ direction, and Okazaki fragments make this possible on the 3’ -> 5’ strand

Question 16

What does Tus (termination utilization substance) do?

Answer 16

Binds to ter sequences (termination sequences) and prevents the advancement of the replication fork

Question 17

In which strand (leading or lagging) are multiple RNA primers made?

Answer 17

The lagging strand, because each Okazaki fragment must start at an RNA primer

Question 18

What is a catanane?

Answer 18

In bacterial cells, the two newly replicated DNA strands are intertwined, and topoisomerase II cuts them apart and reattaches them separately from each other