Unit 4: SAC 1.5: DNA replication

Question 1

What is DNA replication?

Answer 1

DNA replication is the process of copying the nucleic compounds that make up a strand of DNA for mitosis and meiosis to occur.

Question 2

What is Helicase?

Answer 2

Helicase is an enzyme that breaks the hydrogen bonds between base pairs to unwind the double helix. These unwound sections are used as templates to create two complimentary DNA strands (which run antiparallel).

Question 3

What is RNA primase?

Answer 3

Before DNA polymerase can add matching nucleotides to complimentary bases, the enzyme RNA primase first needs to add a short section of RNA (an RNA primer) to the DNA’s origin of replication.

Question 4

What is DNA polymerase.

Answer 4

Once an RNA primer has been added to the origin or replication, the enzyme DNA polymerase can then add free flowing, matching nucleotides on the main steam all the way down the molecule.

Question 5

Explain the leading strand.

Answer 5

On the leading stand (which is formed in a 5’-3’ direction), DNA polymerase which also only adds bases in a 5’-3’ direction can therefore make the leading strand in one continuos process.

Question 6

Explain the lagging strand.

Answer 6

The lagging strand, which is made antiparallel to the leading strand is formed in a 3’-5’ direction. As DNA polymerase can only copy strands in a 5’-3’ direction; RNA primase must first lay an RNA primer to allow DNA polymerase to be effective. This process then continues in discontinuously in a number of short segments with each one called an Okazaki fragment.

Question 7

What is DNA ligase?

Answer 7

After RNA primase and DNA polymerase take effect, the enzyme DNA ligase then moves along the new DNA, removing RNA primers and replacing them with free nucleotides. DNA ligase then links all bases together.

Question 8

What is the final step in DNA replication?

Answer 8

Termination, in which as the DNA is copied the nitrogenous bases reform their hydrogen bonds and the DNA strands re-wind to form a double helix. This double helix contains one old and one new strand based on the Meselson- Stahl experiment.

Question 9

Explain Binary Fission and its steps.

Answer 9

Binary fission is a form of DNA replication that occurs in prokaryotic cells such as bacteria. Once a bacteria cell reaches full size, binary fission takes place:

1. The two strands of DNA attach to the plasma membrane.
2. The cell elongates, dragging a copy of the new replicates into each end of the bacteria.
3. The bacteria forms a septum and divides, forming two now identical cells.