Lec1 | DNA Replication

Question 1

What is the function of DNA replication or synthesis?

Answer 1

DNA replication or synthesis is the process by which a cell makes an identical copy of its DNA before cell division.

Question 2

Why is DNA replication essential?

Answer 2

DNA replication is essential for the transmission of genetic information from one generation of cells to the next.

Question 3

Where does DNA replication occur in eukaryotic cells?

Answer 3

DNA replication occurs in the nucleus of eukaryotic cells.

Question 4

Where does DNA replication occur in prokaryotic cells?

Answer 4

DNA replication occurs in the cytoplasm of prokaryotic cells.

Question 5

During which phase of the cell cycle does DNA replication occur?

Answer 5

DNA replication occurs in the Interphase (S phase).

Question 6

What does it mean that DNA replication is semi-conservative?

Answer 6

Each strand in a DNA molecule serves as a template for synthesis of a new, complementary strand.

Question 7

What is one result of the semi-conservative nature of DNA replication regarding genetic information?

Answer 7

The semi-conservative nature of DNA replication ensures that the genetic information is accurately transmitted from one generation of cells to the next.

In addition to that, semi-conservative DNA replication allows for genetic variation to arise through mutations, which can occur during DNA replication.

Question 8

What are the three steps of DNA replication?

Answer 8

• Initiation.
• Elongation.
• Termination.

Question 9

What initiates DNA replication?

Answer 9

Pre-replication protein complexes locate the origin of replication.

Question 10

What enzyme temporarily breaks the DNA backbone to unwind it?

Answer 10

Topoisomerase temporarily breaks the DNA backbone to unwind it.

Question 11

What enzyme ‘unzips’ DNA by breaking hydrogen bonds?

Answer 11

Helicase ‘unzips’ DNA by breaking hydrogen bonds.

Question 12

What molecules stabilize unwound DNA during replication?

Answer 12

Single-Stranded Binding Proteins stabilize the unwound DNA.

Question 13

What is the ‘Y’ shaped structure formed during DNA replication?

Answer 13

The ‘Y’ shaped structure formed during DNA replication is called a replication ‘fork’.

Question 14

How is each strand of DNA replicated during the initiation step?

Answer 14

Each strand of DNA acts as a template and is replicated differently.

Question 15

What enzyme adds an RNA primer during elongation of the leading strand?

Answer 15

During leading strand elongation, the enzyme primase adds an RNA primer.

Question 16

What does the RNA primer on the leading strand provide?

Answer 16

The RNA primer on the leading strand provides the starting point for synthesis by providing OH-.

Question 17

Which enzyme adds new nucleotides to the leading strand after the primer during elongation?

Answer 17

During leading strand elongation, DNA polymerase (δ & ε) adds new nucleotides to the primer.

Question 18

What is the direction of the synthesis of DNA for leading strand during elongation?

Answer 18

The direction of DNA synthesis on the leading strand during elongation is in the 5’ to 3’ direction.

Question 19

How is DNA replication on the leading strand described?

Answer 19

Replication on the leading strand is described as continuous.

Question 20

On the lagging strand, how are RNA primers added during the elongation phase?

Answer 20

On the lagging strand during the elongation phase, numerous RNA primers are added at various points along the strand.

Question 21

What are the short DNA segments synthesized on the lagging strand?

Answer 21

Short DNA segments synthesized on the lagging strand are called Okazaki fragments.

Question 22

What is the direction of synthesis for Okazaki fragments during lagging strand elongation?

Answer 22

Okazaki fragments on the lagging strand during elongation are also synthesized in the 5’ to 3’ direction.

Question 23

How is DNA replication described on the lagging strand during the elongation phase?

Answer 23

DNA replication on the lagging strand during elongation is described as discontinuous.

Question 24

During termination, what needs to happen to the Okazaki fragments created on the lagging strand?

Answer 24

During termination, Okazaki fragments on the lagging strand need to be joined together.

Question 25

What is the consequence of RNA primer removal in termination?

Answer 25

RNA primer removal leaves a gap in the DNA molecule during termination.

Question 26

During termination what fills the gaps created by removal of RNA primers?

Answer 26

During termination, DNA polymerase fills the gaps left by RNA primer removal.

Question 27

What enzyme forms phosphodiester bonds, joining Okazaki fragments into a single unified strand during termination?

Answer 27

DNA ligase forms phosphodiester bonds during termination, joining Okazaki fragments.

Question 28

At the end of replication, how does the length of the lagging strand compare to the leading strand?

Answer 28

At the end of replication, the lagging strand is shorter than the leading strand.

Question 29

Why can't the RNA primer at the end of the lagging strand be replaced with DNA nucleotides?

Answer 29

The RNA primer at the end of the lagging strand cannot be replaced with DNA nucleotides, because there is no free 3' OH group for DNA polymerase to add to.

Question 30

What is the consequence of not being able to replace the RNA primer at the end of the lagging strand?

Answer 30

The inability to replace the RNA primer at the end of the lagging strand leaves a gap in the newly synthesized DNA.

Question 31

Specifically, which end of the new strand is not replicated?

Answer 31

Specifically, the extreme 5' end of the newly synthesized strand is not replicated.

Question 32

How does telomerase bind to the telomere?

Answer 32

Telomerase binds to the 3' overhang of the telomere via its internal telomerase RNA primer.

Question 33

What is the general function of telomerase in the cell?

Answer 33

Telomerase extends the telomere.

Question 34

Which DNA polymerase is capable of extending the RNA primer?

Answer 34

DNA Polymerase -α is capable of extending the RNA primer.

Question 35

After the RNA primer is extended, what is synthesized?

Answer 35

After the RNA primer is extended, a complimentary strand is synthesized.

Question 36

Approximately how many nucleotides need to be inserted correctly during each replication of a human diploid cell?

Answer 36

Each time the DNA of a human diploid cell replicates, 6 billion nucleotides need to be inserted in the correct order.

Question 37

Are DNA polymerases always completely accurate in inserting nucleotides?

Answer 37

No enzyme is 100% efficient, and DNA polymerases will occasionally make mistakes, inserting the wrong nucleotide.

Question 38

How are the majority of errors during DNA replication corrected?

Answer 38

In the great majority of cases, errors during DNA replication are quickly corrected by the DNA polymerase itself.

Question 39

What special exonuclease activity does DNA polymerase β have?

Answer 39

DNA polymerase β has an intrinsic 3' → 5' exonuclease activity with a proofreading function.

Question 40

What is the function of topoisomerases in DNA replication?

Answer 40

Topoisomerases relieve the torsional strain that builds up ahead of the replication fork by breaking and re-joining the DNA strands.

Question 41

What is the role of helicase during DNA replication?

Answer 41

Helicase unwinds the double-stranded DNA molecule at the replication fork by breaking the hydrogen bonds between the two strands.

Question 42

What is the function of single-stranded binding proteins (SSBs)?

Answer 42

Single-stranded binding proteins bind to the single-stranded DNA at the replication fork and prevent the strands from re-forming into a double-stranded structure.

Question 43

What is the role of primase in DNA replication?

Answer 43

Primase synthesizes short RNA primers on each strand of DNA at the replication fork.

Question 44

What purpose do the RNA primers synthesized by primase serve?

Answer 44

RNA primers provide a starting point for DNA synthesis by another enzyme called DNA polymerase.

Question 45

What is the function of DNA polymerase (δ & ε) during DNA replication?

Answer 45

DNA polymerase (δ & ε) catalyses the addition of nucleotides to the 3' end of the RNA primer, extending the new DNA strand in the 5' to 3' direction.

Question 46

What is the role of DNA polymerase α?

Answer 46

DNA polymerase α extends complementary strand from the RNA primer to help in end of replication problem.

Question 47

What role does DNA polymerase β play in DNA replication?

Answer 47

DNA polymerase β has a proofreading function that helps to maintain the fidelity of DNA replication.

Question 48

What is the function of exonuclease?

Answer 48

Exonuclease cleaves the RNA strand (primer).

Question 49

What is the role of DNA ligase?

Answer 49

DNA ligase joins the Okazaki fragments on the lagging strand together to form a continuous DNA strand.