| when is replication initiated? | at the bacterial origin when a cell passes a critical threshold of size. |
| what is a replicon? | A unit of the genome in which DNA is replicated. Each contains an origin for initiation of replication. |
| what is the origin? | A sequence of DNA at which replication is initiated. |
| what is the terminus? | A segment of DNA at which replication ends. |
| what is single-copyreplicationcontrol and multicopyreplicationcontrol? | single-copyreplicationcontrol control system in which there is only one copy of a replicon per unit bacterium,– The bacterial chromosome and some plasmids have this type of regulation.multicopyreplicationcontrol–Occurswhen the control system allows the plasmid to exist in more than one copy per individual bacterial cell. |
| what is semiconservative replication? | Replication accomplished by separation of the strands of a parental duplex, with each strand then acting as a template for synthesis of a complementary strand. |
| what appears as a bubble within nonreplicated DNA? | A replicated region |
| what is the replication fork? | is initiated at the origin and then moves sequentially along DNA. |
| what are the types of replication? | unidirectional replication when a single replication fork is created at an origin. bidirectional replication when an origin creates two replication forks that move in opposite. |
| how is does the Bacterial Genome replicate? | Bacterial replicons are usually circles that replicate bidirectionally from a single origin.
The origin of E. coli, oriC, is 245 bp in length. |
| how does Methylation of the Bacterial Origin Regulates Initiation? | oriC contains binding sites for DnaA: dnaA-boxes.
• oriC also contains 11 GATC/CTAG repeats that are
methylated on adenine on both strands. |
| what does Replication generates? | hemimethylated DNA, which cannot initiate replication.
• There is a 13-minute delay before the GATC/CTAG repeats are remethylated. |
| what does Initiation at oriC require? | requires the sequential assembly of a large protein complex on the membrane.
• oriC must be fully methylated.
• DnaA-ATP (a licensing factor) binds to short repeated sequences and forms an oligomeric complex that melts DNA. |
| what does Creating the Replication Forks at the Origin oriC involve ? | Six DnaC monomers bind each hexamer of DnaB, and this complex binds to the origin.
• A hexamer of DnaB (a helicase) forms the replication fork. Gyrase and single-strand binding proteins (SSB) are also required.
• A short region of A-T–rich DNA is melted.
• DnaG primase is bound to the helicase complex and creates the replication forks. |
| what are the Mechanisms Exist to Prevent Premature Reinitiation of Replication? | SeqA binds to hemimethylated DNA and is required for delaying rereplication.
• SeqA may interact with DnaA.
• As the origins are hemimethylated they bind to the cell membrane and may be unavailable to methylases.
• The dat locus contains DnaA-binding sites that titrate availability of DnaA protein.
• Hda protein is recruited to the replication origin to convert DnaA-ATP to DnaA-ADP. |
| do Archaeal Chromosomes Contain Multiple Replicons? | Some archaea have multiple replication origins.
• These origins are bound by homologs of eukaryotic replication initiation factors. |
| do Eukaryotic Chromosome Contains Many Replicons? | A chromosome is divided into many replicons.
• The progression into S phase is tightly controlled. |
| how large are the replicons in eukaryotic cell? and how are they activated? | Eukaryotic replicons are 40 to 100 kb in length.
• Individual replicons are activated at characteristic times during S phase.
• Regional activation patterns suggest that replicons near one another are activated at the same time. |
| what are the Origins that Can Be Isolated in Yeast? | Origins in S. cerevisiae are short A-T sequences that have an essential 11-bp sequence.
• The ORC is a complex of six proteins that binds to an ARS. |
| what is the domain of the Replication Origins Can Be Isolated in Yeast? where can related ORC be found? | The conserved 11-bp sequence of A-T base pairs in the yeast ARS element that comprises the replication origin.Related ORC complexes are found in multicellular eukaryotes. |
| what are Licensing factor ? | it is necessary for initiation of replication at each origin.
• Licensing factor is present in the nucleus prior to replication, but is removed, inactivated, or destroyed by replication. |
| what are the Licensing Factor that Bind to ORC? | The ORC is a protein complex that is associated with yeast origins throughout the cell cycle.
• Cdc6 protein is an unstable protein that is synthesized only in G1.
• Cdc6 binds to ORC and allows MCM proteins to bind.
• Cdt1 facilitates MCM loading on origins.
•When replication is initiated, Cdc6 and Cdt1 are displaced. The degradation of Cdc6 prevents reinitiation. |
| what are prereplication complex and postreplication complex? | prereplication complex – A protein-DNA complex at the origin in S. cerevisiae that is required for DNA replication. The complex contains the ORC complex, Cdc6, and the MCM proteins.postreplication complex – A protein-DNA complex in S. cerevisiae that consists of the ORC complex bound to the origin. |
| what's a checkpoint? | A biochemical control mechanism that prevents the cell from progressing from one stage to the next unless specific goals and requirements have been met. |
