Course Guide Chapter 14: DNA Structure and Replication

Question 1

What is the function of topoisomerase I in DNA replication?

Answer 1

relaxes the supercoiled DNA

Question 2

What is the function of helicase in DNA replication?

Answer 2

unwinds the double helix into single stranded (ssDNA)

Question 3

What is the function of SSB in DNA replication?

Answer 3

single-stranded DNA binding protein; stabilizes the ssDNA

Question 4

What is the function of primase in DNA replication?

Answer 4

synthesizes RNA primers

Question 5

What is the function of DNA polymerase I in DNA replication?

Answer 5

erases RNA primers and fills in the gaps

Question 6

What is the function of DNA polymerase III in DNA replication?

Answer 6

DNA replication, proof reading and repair

Question 7

What is the function of DNA ligase in DNA replication?

Answer 7

covalently joins free 3’ and 5’ ends of two DNA strands

Question 8

What is the function of DNA gyrase in DNA replication?

Answer 8

introduces supercoiling in DNA

Question 9

What is the first step of DNA replication?

Answer 9

supercoiling relaxed at the origin of replication by topoisomerase

Question 10

After supercoiling relaxed at the origin of replication by topoisomerase, what is the next step of DNA replication?

Answer 10

relaxed DNA helix opened to make a replication fork by helicase

Question 11

After relaxed DNA helix opened to make a replication fork by helicase, what is the next step of DNA replication?

Answer 11

resulting single stranded DNA is stabilized by single stranded DNA binding (SSB) proteins

Question 12

After resulting single stranded DNA is stabilized by single stranded DNA binding (SSB) proteins, what is the next step of DNA replication?

Answer 12

primase makes an RNA primer to start the new DNA synthesis

Question 13

After primase makes an RNA primer to start the new DNA synthesis, what is the next step of DNA replication?

Answer 13

DNA polymerase III binds to the DNA template + RNA-primer and adds nucleotides complementary to the template strand

Question 14

After DNA polymerase III binds to the DNA template + RNA-primer and adds nucleotides complementary to the template strand, what is the next step of DNA replication?

Answer 14

new DNA synthesis occurs in the 5’ to 3’ direction on a template that runs in the 3’ to 5’ direction

Question 15

After new DNA synthesis occurs in the 5’ to 3’ direction on a template that runs in the 3’ to 5’ direction, what is the next step of DNA replication?

Answer 15

a leading strand is synthesized continuously from 5’ to 3’ based on the template

Question 16

After a leading strand is synthesized continuously from 5’ to 3’ based on the template, what is the next step of DNA replication?

Answer 16

DNA is synthesized in small fragments called Okazaki fragments in the lagging strand

Question 17

After DNA is synthesized in small fragments called Okazaki fragments in the lagging strand, what is the next step of DNA replication?

Answer 17

once the new strand is synthesized, DNA polymerase III proofreads it and removes errors. DNA polymerase I removes the RNA primer and completes the DNA strand

Question 18

After once the new strand is synthesized, DNA polymerase III proofreads it and removes errors. DNA polymerase I removes the RNA primer and completes the DNA strand, what is the last step of DNA replication?

Answer 18

once the small fragments are completed, DNA ligase joins the two ends of DNA strands to complete DNA replication. DNA gyrase facilitates supercoiling the DNA to compact the chromosomes into nucleosomes

Question 19

What is mismatch repair of DNA?

Answer 19

done to correct errors made during DNA replication. DNA polymerase makes approximately 1 mistake in 10,000 base pairs. Then it proofreads the newly-made DNA, removes the wrong bases and repairs the DNA to minimize the errors to 1 in a billion. These error corrections use the mismatch repair mechanism by checking complementary base pairing

Question 20

What is telomere repair or preservation of DNA?

Answer 20

occurs during DNA replication and is catalyzed by telomerase; helps prevent the telomere from getting shortened after each cell cycle. Telomerase temporarily extends the telomere region to allow the RNA primer to bind for DNA replication and once it is replicated, the extended region annealed to the RNA primer is removed to maintain the same length of telomere

Question 21

What is excision repair of DNA?

Answer 21

occurs after a cell divides and in in the G1 or G2 phase. This damage is caused by carcinogens and mutagenic radiations altering the bases or making pyrimidine dimers. Such mutations are constantly monitored by over 50 different enzymes and corrected by excising the damaged strand of DNA and making a new matching strand in its place