4BY535_2024_02_replication

Definition: DNA replication is the process through which a cell copies its entire genome to ensure that each daughter cell has a complete set of DNA during cell division.

Fundamental Biological Process: Understanding DNA replication is essential for grasping biological concepts, particularly in genetics.
Forensic Science Application: Techniques such as Polymerase Chain Reaction (PCR), which rely on DNA replication, are crucial in forensic science for amplifying DNA samples.

What is replication?: It refers to the process of copying DNA, which is necessary for cell division and organismal reproduction.
Why is replication necessary?: It ensures that each new cell receives an exact copy of the parent cell's DNA, maintaining genetic continuity.

Semiconservative Model: Each new double helix consists of one original strand and one newly synthesized strand. Following one round of replication, there are two molecules with half old and half new material.
Conservative Model: The entire parental DNA strand serves as a template to create a new, fully double-stranded molecule, conserving the old strands.
Dispersive Model: Parental strands are broken into pieces, and the new DNA contains segments of old and new DNA distributed randomly.

The Meselson-Stahl experiment confirmed the semiconservative model using E. coli grown in nitrogen isotopes (15N and 14N).
Observation: Following centrifugation, heavy and light DNA strands demonstrated the semiconservative nature of replication, where DNA incorporated both isotopes after each round of replication.

Initiation: Begins at the origin of replication where replication proteins bind, and helicase unwinds the DNA, forming replication forks.
Elongation: DNA polymerase synthesizes new DNA strands in a 5' to 3' direction, guided by RNA primers.
Termination: Occurs when replication forks meet or when the DNA sequence is fully replicated, resulting in completed daughter strands.

Proteins like DnaA bind to the origin of replication, causing the DNA double helix to unwind and form single-stranded regions.
Single-Stranded Binding Protein (SSB) stabilizes these strands and prevents them from reannealing or being degraded by nucleases.
DnaB and DnaC: These helicases unwind the DNA and subsequently prepare the site for replication.

DNA Primase synthesizes a short RNA primer to initiate DNA synthesis.
The Leading Strand is synthesized continuously toward the replication fork, while the Lagging Strand, synthesized discontinuously through Okazaki fragments, is constructed away from the fork.
DNA Polymerases: Key enzymes involved include DNA Polymerase I (removes RNA primers) and DNA Polymerase III (responsible for DNA synthesis).

During termination, RNA primers are replaced with DNA nucleotides, and the newly synthesized DNA strands are sealed by DNA ligase to create a continuous DNA strand.
Key Termination Points: Prokaryotic replication usually involves a single termination point, while eukaryotic replication can terminate where two replication bubbles meet.

Origins of Replication: Prokaryotic cells have a single origin, whereas eukaryotic cells have multiple origins of replication to facilitate rapid synthesis.
Elongation and Termination: Prokaryotes and eukaryotes differ in the enzymes involved, sizes of Okazaki fragments, rates of replication, and structures formed post-replication.

Origin of Replication: The sequence at which DNA replication initiates.
Leading and Lagging Strands: The leading strand is synthesized continuously, while the lagging strand is synthesized in segments (Okazaki fragments).