Summary of "Cell Biology | DNA Replication 🧬"

Key Scientific Concepts:

Purpose of DNA Replication: DNA Replication is necessary for cell division, allowing cells to make identical copies of themselves during the Cell Cycle.
Cell Cycle Phases: The Cell Cycle consists of G1, S phase (where DNA Replication occurs), G2, and mitosis.
Semi-Conservative Model: DNA Replication follows a Semi-Conservative Model, where each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.
Directionality of Replication: DNA Replication occurs in a 5' to 3' direction, where nucleotides are added to the 3' end of the growing strand.
Bi-Directional Replication: Replication occurs in both directions from the origin of replication, creating replication forks.

Initiation:
- Identification of the origin of replication, rich in adenine and thymine.
- Binding of the pre-replication protein complex to separate the DNA strands.
- Formation of a replication bubble.
Unwinding:
- Helicase enzymes unwind the DNA at replication forks, creating single-stranded DNA.
- Single-stranded binding proteins stabilize the separated strands to prevent re-annealing.
- Topoisomerases alleviate supercoiling caused by unwinding.
Elongation:
- Primase synthesizes RNA primers to provide a starting point for DNA polymerases.
- DNA Polymerase III synthesizes new DNA strands in a 5' to 3' direction, using the parental strand as a template.
- Leading strand is synthesized continuously, while the lagging strand is synthesized in short segments called Okazaki Fragments.
Removal of RNA Primers:
- DNA Polymerase I removes RNA primers and fills in the gaps with DNA.
- DNA ligase seals the nicks between Okazaki Fragments on the lagging strand.
Termination:
- DNA Replication concludes when replication forks meet, and DNA polymerases detach.
- Telomeres shorten with each replication cycle, protecting essential coding DNA from being lost.

Telomeres: Non-coding regions at the ends of chromosomes that shorten with each replication cycle, preventing loss of important genetic information.
Telomerase: An enzyme that elongates Telomeres in certain cells (e.g., stem cells and cancer cells) to maintain their length and enable continued cell division.