M2 DNA (Replication)

Question 1

DNA Replication Steps (8 Steps)

Answer 1

1. DNA Helicase unzips and separates the 2 strands resulting in the formation of a replication fork.
2. Enzymes Topoisomerase and DNA gyrase is used in preventing DNA from getting tangles and relieving pressure in supercoiled DNA reducing torsional strain.
3. Enzyme Primase makes DNA primers marking the starting point for the construction of DNA
4. Enzyme DNA Polymerase binds to the primer and adds the DNA base pairs in the 5’ to 3’ direction. This is done via complementary base pairing.
5. Leading strand of DNA is made continuously as DNA polymerase works in one direction. The lagging strand cannot be made like this as it is anti-parallel. DNA polymerase makes these strands in small fragments called Okazaki fragments.
6. Each fragment is started with an RNA primer and DNA polymerase adds a short row of DNA bases in the 5’ to 3’ direction and the next one is made further down the strand.
7. Once the DNA has been made, the Enzyme Exonuclease removes all the RNA primers from both strands of DNA. Another DNA polymerase enzyme fills gaps that are left behind.
8. DNA Ligase seals up the Okazaki fragments of DNA in both strands to form a continuous double strand.

Question 2

Features of DNA

Answer 2

Semi conservative as one strand is old and conserved and the other strand is new.

Anti-parallel strands
Double Helix Strands

Purine always pairs to a pyrimidine.

DNA:
Adenine – Thymine (2 hydrogen bonds)
Guanine — Cytosine (3 hydrogen bonds)