DNA is crucial for coding traits and guiding cellular functions.
DNA replication is essential for cell division to ensure new cells receive DNA.
Occurs in the nucleus of eukaryotic cells; prokaryotic cells also replicate DNA but with differences.
Timing of DNA Replication
Occurs before cell division, specifically before mitosis or meiosis during interphase in eukaryotic cells.
Key Enzymes in DNA Replication
Helicase: Unzips the DNA by breaking hydrogen bonds between bases.
DNA Polymerase: Builds new DNA strands by replicating DNA molecules.
Primase: Initializes the process by creating RNA primers, guiding DNA polymerase on where to start.
Ligase: Glues together DNA fragments.
DNA Replication Process
Initiation
Begins at the origin identified by specific DNA sequences.
Helicase unwinds the DNA.
Single-stranded binding proteins (SSB) prevent the strands from rejoining.
Topoisomerase controls supercoiling.
Elongation
Primase makes RNA primers for DNA polymerase.
DNA polymerase adds new nucleotides in a 5’ to 3’ direction.
DNA strands are antiparallel; one is the leading strand (continuous synthesis) and the other is the lagging strand (discontinuous, forms Okazaki fragments).
RNA primers on Okazaki fragments are replaced with DNA, and ligase seals gaps.
Completion
Results in two identical double helix DNA molecules formed from the original.
Known as "semi-conservative" replication because each new DNA molecule contains one old and one new strand.
Importance of Proofreading
DNA polymerase possesses proofreading ability to minimize errors in base pairing.
Prevents incorrect coding which could lead to faulty proteins.
Significance
Understanding DNA replication has led to medical advancements, such as treatments targeting DNA replication in harmful cells like cancer.
Emphasis on further exploration beyond the basics to understand the detailed mechanisms and applications.