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MoleGen Ch 9
Replication
| Term | Definition |
|---|---|
| primer | a short strand of DNA that is chemically modified and serves as the starting point for DNA synthesis |
| primer:template junction | a particular arrangment of ssDNA and dsDNA |
| template | Provides the ssDNA that directs the additiom of each complementary deoxynucleotide. Provides the information necessary to selectwhich nucleotide are added |
| DNA polymerase | the synthesis of DNA is cataylzed by a class of enzymes |
| processivity | is a characteristic of enzymes that operate on polymeric substrates. |
| degree of processivity | the average number of nucleotides addede ach time the enzyme binds a primer:template junction |
| proofreading exonuclease | this type of enzyme degrades DNA starting from the 3' DNA end (the removal of incorrect base-pair nucleotides) |
| exonnucleases | nucleases that can only degrade from a DNA end |
| endonucleases | nucleases that can cut within a DNA strand |
| replication fork | the junction between the newly separated templates strands and the unreplicated duplex DNA |
| leading strand | the newly synthesized DNA strand directed by elongating the 3' end |
| lagging strand | the DNA poymerase moves in the opposite direction of the replication fork (starts from the 5' end) |
| okazaki fragments | short fragments of new DNA formed on the lagging strand |
| primase | a specialized RNA polymerase dedicated to making short RNA primers on an ssDNA template |
| DNA helicase | unwinds the DNA at the replication fork, creating an ssDNA template that can be acted on by primase |
| RNase H | Recognizes and removes most of each RNA primer |
| DNA ligase | the gap in the phosphodiester backbone can be repaired by this enzyme |
| DNA helicases | catalyze the separation of the two strands of duplex DNA . |
| polarity | Each DNA helicase moves along ssDNA in a defined direction 5' -> 3' or 3' -> 5' |
| ssDNA-binding proteins | to stablize the separated strands, SSBs binds to the separated strands |
| cooperative binding | SSB bound to immediately adjacent regions of ssDNA also Bind to each other |
| topoisomerases | the supercoils introduced by the action of the DNA helicase are removed by topoismerases that act on the unreplicated dsDNA in front of the replication fork |
| DNA polymerase III | primary enzyme involved in the replication of the chromosome |
| DNA Pol III holoenzyme | a large complex that confers very high processivity |
| DNA polymerase I | specialized for the removal of the RNA primers that are used to initiate DNA synthesis |
| polymerase switching | the process of replacing DNA pol a/primase with DNA POL s or POL e . Results in three different DNA polymerase functioning at the eukaryotic replication fork |
| sliding DNA clamps | prevents the DNA polymerase from diffusing away from the DNA by keeping it in close proximity to the DNA. |
| replisome | The combination of all the proteins that function at the replication fork |
| origins of replication | the site at which DNA unwinding and initation of replication occur |
| replicon | all of DNA replicated from a particular origin of replication |
| replicator | the cis-acting DNA sequence that are sufficient to direct the initiating of DNA replication |
| initiator | recognizes a DNA element in the replicator and activates the initiation of replication |
| origin recognition complex | multi-subunit DNA binding complex that binds in all eukaryotes in an ATP- dependent manner to origins of replication |
| type II topoisomerases | separate the chromosomes into separate daughter cell, the two circular DNA molecules must be diengage from each other and is accomplished by this enzyme |
| end replication problem | the requirement for an RNA primer to initiate all new DNA synthesis creats a dilemma for the replication of the ends of linear chromosomes |
| telomeres | the end sequence of chromosomes which are composed of TG-rich DNA sequence. 5'-TTAGGG-3' |
| telomerase | adds the telomeric sequence to the 3' terminus at the end of the chromosomes |
| sliding clamp loaders | catalyze the opening and placement of sliding clamps on the DNA |