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mol. genetics ch 11
DNA replication
| Question | Answer |
|---|---|
| what is DNA polymerase? | an enzyme that synthesizes a new DNA strand on top of a template strand |
| in what direction does DNA polymerase go? | they synthesize DNA in a 5' to 3' direction on a strand that is 3' to 5' |
| when does DNA synthesis occur? | it occurs during the S phase |
| how does DNA polymerase proofread? | A 3’-5’ exonuclease activity is used to excise bases that have been added to DNA incorrectly |
| what kinds of errors does DNA polymerase make? | base substitution when the wrong nucleotide is placed in the DNA sequence, and frameshift when an extra nucleotide is inserted or omitted |
| what is the leading strand? | the strand that is in a 3' to 5' direction |
| what is the lagging strand? | the strand that is in a 5' to 3' |
| what is an okazaki fragment? | fragments that are joined together on the lagging strand, DNA polymerase cannot continuously synthesize DNA on this strand. |
| how are okazaki fragments covalently linked? | by DNA ligase, which catalyzes the formation of phosphodiester bonds between the -hydroxyl end of one fragment and the -phosphate end of the next. |
| what is helicase? | an enzyme that separates DNA strands by encircling one strand, binds to duplex DNA and separates base pairs, then releases the duplex. it requires energy from the hydrolysis of ATP |
| what are single-stranded binding proteins? | a protein that binds to the single-stranded DNA, protecting and preventing it from reforming the duplex state. |
| why is a primer needed to start DNA replication? | because DNA cannot initiate replication, they can only enlongate a previously started new DNA strand. DNA polymerase requires this primer which is a 3' -OH priming end. |
| how often is a primer for the initiation of DNA replication needed? | every single time DNA replication occurs, the placement of a primer is needed to initiate replication |
| what is primase? | an enzyme that is required to catalyze the actual priming reaction. |
| how is DNA replication terminated in E. coli? | the two clusters of ter sites in ecoli are binded by a protein called Tus, which prevents the replication fork from proceeding. If one fork fails to meet in the middle, the faster fork is trapped in the middle to wait for the lagging fork. |
| what is a ter site? | a short sequence of about 23 base pairs that is unidirectional and is involved with the termination of replication in e.coli |
Created by:
angievelasco
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