Chapter 9

Question 1

What are the 8 components of replication in bacterial cells?

Answer 1

Initiator proteins
DNA helicase
Single-stand binding proteins
DNA gyrase
DNA primase
DNA polymerase III
DNA polymerase I
DNA ligase

Question 2

What is the function of Initiator proteins?

Answer 2

Bind to origin and separate strands of DNA to initiate replication.

Question 3

What is the function of DNA helicase?

Answer 3

Unwinds DNA to initiate replication

Question 4

What is the function of single-strand binding proteins?

Answer 4

Attach to single-stranded DNA and prevent secondary structures from forming

Question 5

What is the function of DNA gyrase?

Answer 5

Helps with the winding and unwinding of the DNA that occurs during replication and transcription

Moves ahead of the replication fork, making and resealing breaks in the double-stranded helical DNA to release the torque that builds up as a result of unwinding at the replication fork

Question 6

What is the function of DNA primase?

Answer 6

Synthesizes a short RNA primer to provide a 3’ -OH group for the attachment of DNA nucleotides

Question 7

What is the function of DNA polymerase III?

Answer 7

Elongates a new nucleotide strand from the 3’ -OH group provided by the primer

Question 8

What is the function of DNA polymerase I?

Answer 8

Removes RNA primers and replaces them with DNA

Question 9

What is the function of DNA ligase?

Answer 9

Joins Okazaki fragments by sealing breaks in the sugar-phosphate backbone of newly synthesized DNA.

Question 10

What does one error per million bp lead to?

Answer 10

6400 mistakes every time a human cell divides- DNA replication needs to be fast and accurate

Question 11

How fast does E. coli replicate? What about eukaryotes?

Answer 11

A rate of 1000 nucleotides per second. Eukaryotes aren’t as fast but have more replication events happening simultaneously.

Question 12

What happened with the Meselson and Stahl Experiment? What does semiconservative replication look like?

Answer 12

Two isotopes of nitrogen (14N common form and 15N rare form) E. coli were first grown in 15N media, then transferred to 14N media. Cultured E. coli were subjected to equilibrium density gradient centrifugation.
Demonstrated that DNA replicated semi-conservatively, meaning that each strand in a DNA molecule serves as a template for the synthesis of a new, complementary strand.

Question 13

What is bidirectional replication? What happens during it?

Answer 13

A type of DNA replication where replication is moving along in both directions from the starting point. This creates two replication forks, moving in opposite directions.

Question 14

What is semi-conservative replication?

Answer 14

The two strands of DNA unwind from each other, and each acts as a template for the synthesis of a new, complementary strand.

Question 15

What is proofreading during DNA replication?

Answer 15

DNA polymerase III and I have 3’ to 5’ exonuclease activity, which removes the incorrectly paired nucleotide.

Question 16

What is the origin of replication?

Answer 16

A sequence from where replication starts and any piece of foreign DNA is linked to this sequence.

Question 17

What are replicons?

Answer 17

Units of replication. It starts at a replication origin.

Question 18

What does the leading strand do?

Answer 18

Undergoes continuous replication. The leading strand is synthesized by adding nucleotides to the 3’ end of the growing strand

Question 19

What does the lagging strand do?

Answer 19

Undergoes discontinuous replication. The lagging strand is synthesized by adding nucleotides to the 5’ end

Question 20

What are the 4 minimum requirements of replication?

Answer 20

1. A template strand
2. Raw material: individual deoxynucleotides in a triphosphate form (dNTPs)
3. DNA polymerases: add nucleotides only to the 3’ end of the growing strand. Replication can only go from 5’ to 3’
4. Primer: short sequence of about 10-12 nucleotides of RNA or DNA that is complementary to a short sequence on the template strand. DNA polymerases need these to initiate replication!

Question 21

What does DNA Replication look like?

Answer 21

Question 22

What does eukaryotic replication look like? What is the typical length of their replicon? What happens to the telomeres?

Answer 22

Linear DNA, thousands of origins, many replicons. Typical replicon length is 200,000-300,000 base pairs in length. Has Bidirectional replication. The telomeres get shorter over more and more replications

Question 23

What are the problems with telomeres in eukaryotes?
-both with aging and cancer

Answer 23

As telomeres get shorter and shorter over time, it causes you to age and get older. Telomerases are frequently reactivated in human cancers, and they allow cancer cells to perpetually divide and essentially become immortalized.

Question 24

What do telomerases do? What does telomerase look like?

Answer 24

They fix the problems associated with telomeres.
Telomerase allows for telomere length and equilibrium maintenance by adding on repeats to the end of the chromosome.

Question 25

What does recombination do? What is homologous recombination?

Answer 25

-Segregation of homologous chromosomes
-The production of genetic variation
-DNA repair
Exchange is between homologous DNA molecules during crossover