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Advantages of bi-directional replication
- Less stress so bonds don�t break
- Energetically favorable
- Enzyme machinery
A free 3� OH is needed to add on DNA
- Pairs with phosphate
- Needs template DNA
- DNTPs � phosphate groups � new nucleotides � phosphodiester bonds
Polymeases have elongagation function
Also 5 to 3 and 3 to 5 exonuclease activity � cuts from the end to repair faulty DNA
DNA Polymerase III and I do what?
Primarily with DNA replication
DNA polymerase II, IV and V do what?
DNA repair � repair nucleotide excision..
RNA primers initiate
- Short strands to build upon
- Provides a free 3� OH
Single Strand Binding protein
Keeps the helices unwound
Toposomerase I and DNA gyrase
Produces breaks in DNA
Telomers � end sequences of DNA at the end of chromosomes
Adds sequence of DNA and provide a 3� OH to add DNA to ends
Telomerase has to be shut off because?
There needs to be a limit to the amount of replication
In Vivo DNA replication occurs
semiconservatively, is initiated at unique origins, and usually proceeds bidirectionally from each origin of replication.
DNA Replication is Semiconservative
- � Each strand serves as a template
- � Complementary base pairing determines the sequence of the new strand
- � Each strand of the parental helix is conserved
DNA replicates by a semiconservative mechanism:
As the two complementary strands of a parental double helix unwind and separate, each serves as a template for the synthesis of a new complementary strand.
The hydrogen-bonding potentials of the bases in the template strands specify complementary base sequences in the nascent DNA strands.
Replication is initiated at unique origins and usually proceeds
bidirectionally from each origin.
DNA Polymerases and DNA Synthesis In Vitro Much of what we know about DNA synthesis was deduced from in vitro studies.
Requirements of DNA Polymerases
- � ?Primer DNA with free 3'-OH
- � ?Template DNA to specify the sequence of the new strand
- � ?Substrates: dNTPs
- � ?Mg2+
Polymerases in E. coli
- � �DNA Replication: DNA Polymerases III and I
- � �DNA Repair: DNA Polymerases II, IV, and V
Polymerases in Eukaryotes
- � �Replication of Nuclear DNA: Polymerase alpha, sigma and/or epislon
- � �Replication of Mitochondrial DNA: Polymerase gamma
- � �DNA Repair: Polymerases beta, epsilon�
- � All of these enzymes synthesize DNA 5' to 3' and require a free 3'-OH at the end of a primer
DNA synthesis is catalyzed by enzymes called
All DNA polymerases require a _____strand, which is extended, and a ____strand, which is copied.
All DNA polymerases have an absolute requirement for a free ____on the primer strand, and all DNA synthesis occurs in the 5' to 3' direction.
The 3' to 5' exonuclease activities of DNA polymerases proofread nascent strands as they are synthesized, removing any mispaired nucleotides at the 3' termini of primer strands.
DNA replication is a complex process, requiring the concerted action of a large number of proteins.
Synthesis of the leading strandis
Synthesis of the lagging strandis
The new DNA is synthesized in short segments called ___that are later joined together.
DNA Ligase Covalently
Closes Nicks in DNA
RNA Primers are Used to
Initiate DNA Synthesis
Unwinds the Parental Double Helix
Supercoiling of Unwound DNA
- DNA Topoisomerase I Produces Single-Strand Breaks in DNA
- DNA Topoisomerase II Produces Double-Strand Breaks in DNA
DNA replication is complex, requiring the participation of a large number of proteins.
DNA synthesis is continuous on the progeny strand that is being extended in the overall 5' to 3' direction, but is ______on the strand growing in the overall 3' to 5' direction.
New DNA chains are initiated by short RNA primers synthesized by
The enzymes and DNA-binding proteins involved in replication assembled into a ______at each replication fork and act in concert as the fork moves along the parental DNA molecule.
DNA Replication in Eukaryotes
- � Shorter RNA primers and Okazaki fragments
- � DNA replication only during S phase
- � Multiple origins of replication
- � Nucleosomes
- � Telomeres
- � Bidirectional Replication from Multiple Origins in Eukaryotes
Eukaryotic Replication Proteins
- ?DNA polymerase alpha-DNA primase�initiation; priming of Okazaki fragments
- ?DNA polymerase sigma�processive DNA synthesis
- ?DNA polymerase epislon�DNA replication and repair in vivo
PCNA (proliferating cell nuclear antigen)�sliding clamp
- Replication factor-C Rf-C)�loading of PCNA
- Ribonuclease H1 and Ribonuclease FEN-1�removal of RNA primers
Telomere Length and Aging
- � Most human somatic cells lack telomerase activity.
- � Shorter telomeres are associated with cellular senescence and death.
- � Diseases causing premature aging are associated with short telomeres.
The large DNA molecules in eukaryotic chromosome replicate bidirectionally from multiple origins.
Two or three DNA polymerases (alpha, sigma and/or epsilon) are present at each replication fork in eukaryotes.
Telomeres, the unique sequences at the ends of chromosomes, are added to chromosome by a unique enzyme called