DNA replication

Question 1

Why is mitotic cell division/replication necessary?

Answer 1

For growth and development and replacement of damaged cells

Question 2

How does a cell prepare for replication?

Answer 2

By:

• Ensuring there is sufficient cellular materials for the new cell as more materials have to be synthesized and stored
• Ensuring there is another copy of its DNA for the new cell

Question 3

What are the key steps that occur in a prokaryotic cell before division?

Answer 3

DNA replication takes place as the cell elongates
As the cell elongates, the growing membrane aids in the transport of the DNA towards the opposite end of the cell
Cell membrane indents
Cell divides and 2 new cells are formed

Question 4

What are the key steps that occur in a eukaryotic cell before it divides?

Answer 4

DNA replication occurs
Separation of replicated DNA
Division of cell, 2 new cells are formed

Question 5

What occurs first before DNA can be replicated (in prokaryotes)?

Answer 5

2 strands of DNA needs to be separated first
The 2 strands of DNA are separated by breaking the hydrogen bonds between the bases, allowing the base sequence to be accessed
Separation is done by helicase

Question 6

What is positive supercoiling?

Answer 6

Unwinding of DNA can cause positive supercoils of DNA further down the replication fork
The stress is then compensated by topoisomerase
Topoisomerase cuts one/both of the DNA strands, to relax the coil and rejoins the DNA molecule

Question 7

Summary of DNA replication (in prokaryotes)

Answer 7

1. Helicase unwinds the parental double helix
2. Single-stranded binding protein stabilize the unwound parental DNA
3. Leading strand is synthesized continuously. Primase will synthesize short RNA primers onto the DNA strand and DNA polymerase will add nucleotides to the free 3’ hydroxyl end. A new DNA strand is formed
4. Lagging strand is synthesized discontinuously. Primase will synthesize short RNA primers onto the DNA strand and DNA polymerase will add nucleotides to the free 3’ hydroxyl end. Okazaki fragments are formed
5. After the RNA primers are replaced by DNA. DNA ligase joins the Okazaki fragments together (in the lagging strand), forming a strand of DNA

Question 7

Summary of DNA replication (in prokaryotes)

Answer 7

1. Helicase unwinds the parental double helix

Question 8

Difference in the DNA replication process in eukaryotes and prokaryotes

Answer 8

• 1 single enzyme in prokaryotes can be represented by multiple enzymes in eukaryotes
• Prokaryotes have a circular chromosome with a single origin of replication
• Eukaryotes have multiple linear chromosomes, each with multiple origins of replication

Question 9

Why is DNA replication considered semi-conservative?

Answer 9

Both original DNA strands are used as template strands, for the synthesis of new DNA strands
Original DNA strands are incorporated into the newly synthesized double helix
Each DNA contains 1 of the original strand and 1 newly synthesized strand