BIO3170 Lecture 3 2024

Leading strand and lagging strand.

It shows that each new DNA molecule consists of one original strand and one newly synthesized strand.

DNA synthesis always proceeds in the 5ʹ→3ʹ direction.

It produces a relaxed circle conformation of the DNA.

It synthesizes RNA primers and extends Okazaki fragments by approximately 10 nucleotides, but lacks 3’ à 5’ exonuclease activity.

1. A primer strand with a free 3' terminus 2. A template strand that is base-paired to the primer 3. A source of dNTPs

New DNA strands are always synthesized in the 5' → 3' direction.

DNA polymerases require a primer to initiate replication.

To ensure that each daughter cell has an exact copy of the genome.

Two hexameric helicases bind at the replication origin in opposite orientations and are activated by a kinase through phosphorylation.

Rfc stands for Replication factor C.

DNA polymerase adds a new dNTP at the 3' end of the primer strand as specified by base-pairing with the template DNA strand.

Primase operates under a bidirectional mechanism of DNA replication.

Short primers that are base-paired to each of the separated parent strands.

Defects in DNA repair are associated with cancers.

They are stitched to the 5ʹ ends of the leading strands by DNA ligase.

Growing Okazaki fragments displace the previous primer, and the elongated fragments are ligated into a continuous strand.

The primary mechanism of DNA replication is semi-conservative replication, where each new DNA molecule consists of one original strand and one newly synthesized strand.

It would take approximately 3 million seconds, or about 34.7 days, to replicate the entire chromosome.

Exactly the same genetic information as the parent cell.

The ORC binds to each replication origin and associates with other proteins required to load two hexameric helicases, oriented in opposite directions.

Topoisomerase I associates with the parental DNA strand ahead of the helicase and removes torsional stress introduced by unwinding of strands.

PCNA acts as a ‘sliding clamp’ to stabilize the polymerase.

Pol δ converts RNA to DNA.

Primase is an RNA polymerase.

The bidirectional mechanism of DNA replication involves two replication forks moving away from the origin of replication, allowing simultaneous synthesis of both strands.

Replisome

Tsuneko and Reiji Okazaki.

There are approximately 37 trillion cells in the human body.

Both linear (eukaryote genomes, viral DNAs) and circular (bacterial genomes, mitochondrial DNA) are subject to torsional stress.

It is responsible for lagging strand synthesis, has high processivity, and possesses 3’ à 5’ exonuclease activity.

Ribonuclease removes RNA.

The lagging strand is synthesized discontinuously from multiple RNA primers formed periodically as each new region of the parent duplex is unwound.

New DNA strands are opposite in polarity to their template DNA strands.

DNA repair mechanisms include base excision repair, nucleotide excision repair, and mismatch repair, which correct various types of DNA damage.

Guanine pairs with Cytosine (G ≡ C) and Adenine pairs with Thymine (A = T).

They conducted an experiment that demonstrated the semi-conservative nature of DNA replication.

Topoisomerase I relieves torsional stress on DNA by cleaving one strand to allow unwinding, producing a relaxed circle conformation.

Eukaryotic chromosomal DNA molecules contain multiple replication origins separated by tens to hundreds of kilobases.

PCNA-Rfc-Pol δ complexes displace the primase-Pol α complexes.

The leading strands (dark green) are generated at each replication fork.

DNA polymerase catalyzes the formation of a phosphodiester bond between the 3' oxygen of the primer strand and the α phosphate of a correctly base-paired dNTP.

DNA is synthesized from deoxyribonucleoside triphosphates (dNTP) precursors.

Okazaki fragments are short sequences of DNA synthesized on the lagging strand during DNA replication, which are later joined together by DNA ligase.

The number of nucleotides in our body is vast, as each cell contains approximately 6 billion base pairs of DNA.

DNA replication.

Leading strand synthesis with high processivity and 3’ à 5’ exonuclease activity.

Helicases use ATP hydrolysis energy to move in opposite directions, unwinding the parent DNA and generating single-stranded templates, which are bound by RPA proteins.

DNA polymerase adds nucleotides to a growing daughter strand in the 5ʹ→3ʹ direction.

Okazaki fragments are produced during the elongation of lagging-strand primers and are initially formed as short segments.

Leading strand synthesis occurs continuously in the direction of the replication fork, while lagging strand synthesis occurs in short segments called Okazaki fragments, away from the fork.

PCNA - Rfc - Pol ε complexes extend the leading strands.

RPA proteins bind to the newly exposed single-stranded regions.

Base excision repair, Nonhomologous end joining, and Homologous recombination.

DNA polymerases require a short, preexisting RNA or DNA primer strand that is base-paired to the template strand.

PCNAc – Rfc – Pol ε complexes replace the primase – Pol α complexes.

Primase synthesizes RNA primers for lagging-strand synthesis at each replication fork.

DNA polymerases are enzymes that synthesize new DNA strands by adding nucleotides complementary to the template strand.

Genetic instability can lead to cancer by increasing the rate of mutations and chromosomal abnormalities, which can disrupt normal cell function and promote uncontrolled cell growth.

Helicases continue to unwind the parent strands during DNA replication.

Copying errors and the effects of various physical and chemical agents.

Replication Protein A (RPA) proteins bind to the separated parent strands at an origin.

The leading strand is synthesized continuously from a single RNA primer at its 5ʹ end.

The main types of eukaryotic DNA polymerases include DNA polymerase α, δ, and ε, each with distinct roles in DNA replication and repair.

Topoisomerases relieve the torsional strain generated ahead of the replication fork by introducing temporary breaks in the DNA strands.