DNA replication Flashcards
(9 cards)
DNA as the genetic material
Hershey-chase experiment : showed that DNA, not protein, carries genetic info using bacteriophages and radioactive labeling
watson and crick, rosalind franklin: discovery of the double-helix structure of DNA
DNA structire and replication
DNA strands are antiparallel 5’ - 3’ and 3’ - 5’
semiconservative replication: each new DNA molecule consist of one old strand and one newly synthesized strand
Replication process and key enzymes
helicase – Unwinds the DNA double helix.
Single-Strand Binding Proteins (SSBs) – Stabilize the unwound strands.
Topoisomerase – Relieves strain ahead of the replication fork.
Primase – Adds an RNA primer to start replication.
DNA Polymerase III – Adds nucleotides in the 5’ to 3’ direction.
DNA Polymerase I – Replaces RNA primers with DNA.
Ligase – Seals gaps between Okazaki fragments on the lagging strand.
leading vs lagging strand syntehsis
Leading strand: Continuous synthesis in the 5’ to 3’ direction.
Lagging strand: Discontinuous synthesis with Okazaki fragments that must be joined by ligase.
DNA proofreading and mutation prevention
DNA Polymerase proofreading: Detects and corrects mismatches.
Mutation causes: Replication errors, mutagens (e.g., UV light, chemicals), and viral infections.
Why do eukaryotic cells have multiple origins of replication, while prokaryotic cells typically have only one?
Eukaryotic cells have multiple origins of replication because their genomes are much larger and organized into linear chromosomes, requiring multiple starting points to efficiently replicate DNA in a timely manner. In contrast, prokaryotic cells have smaller, circular genomes, allowing them to complete DNA replication quickly with just one origin of replication. Multiple origins in eukaryotes help ensure simultaneous replication at different sites, preventing delays in cell division.
Identify the nitrogenous bases in DNA and how they pair in a DNA molecule. What
type of chemical bond connects the “base pairs” of DNA?
The nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). In a DNA molecule, A pairs with T and C pairs with G through complementary base pairing. These base pairs are connected by hydrogen bonds, with A-T pairs forming two hydrogen bonds and C-G pairs forming three hydrogen bonds, contributing to the stability of the DNA double helix.
Describe how DNA replicates itself and why it is called “semiconservative” replication. What are the enzymes involved in DNA replication?
DNA replicates itself through a process called semiconservative replication, meaning that each new DNA molecule consists of one original (parent) strand and one newly synthesized strand. The process begins at origins of replication, where helicase unwinds the DNA helix, creating a replication fork. DNA polymerase then adds complementary nucleotides to the 3’ end of the growing strand, while primase lays down RNA primers to initiate synthesis. Other key enzymes include ligase, which seals gaps between Okazaki fragments on the lagging strand, and topoisomerase, which prevents DNA supercoiling ahead of the replication fork.
Explain why synthesis of the lagging strand is more complex than that of the leading
strand. Include both conceptual and molecular understanding
Synthesis of the lagging strand is more complex than the leading strand because DNA polymerase can only add nucleotides in the 5’ to 3’ direction, but the two DNA strands run antiparallel. Since the leading strand is synthesized continuously in the same direction as the replication fork moves, DNA polymerase can work smoothly. However, the lagging strand must be synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together. This requires primase to lay down multiple RNA primers, DNA polymerase to synthesize each fragment, and ligase to connect the fragments, making the process more complex and fragmented.
