Ch. 11 DNA Replication (part 2) Flashcards
Where are ter sites?
Termination sites for bacterial replicaiton.
Where are the ter sites located?
Multiple directional ter sites are oriented in opposite directions and opposite of the ori in bacterial chromosomes.
What binds to the ter site to initiate replication termination?
Tus binds to ter sites.
What happens if the replication fork runs into a Tus/ter oriented in the opposite direction?
replication fork stops
What happens if the replication fork runs into a Tus/ter oriented in the same direction?
replication fork continues
What do Tus/ter sites ensure?
That replication ends at the same position even if the forks move at different speeds/rates.
What happens to eukaryotic Okazaki fragments to make continuous DNA?
They are ligated
What does the removal of the last Okazaki fragment RNA primer leave?
A gap
What happens if the gap created when the last Okazaki RNA primer is removed is not filled?
What is this called?
The chromosomes eventually shorten and cause cell death.
This is the end replication problem.
What is telomerase?
A reverse transcriptase (TERT) that uses an RNA as a template for DNA
What does telomerase do? (2)
It elongates the 3’ overhang. The enzyme then translocates and repeats this process hundreds to thousands of times.
What does telomerase’s elongation of the 3’ end allow? (2)
It allows additional primers and DNA synthesis to fill in the 5’ end of DNA.
Does the use of telomerase eliminate the gap created by removal of the last Okazaki RNA primer?
No. The gap will still exist, but the telomerase mechanism prevents chromosome shortening during DNA replication.
How are the ends of the elongated eukaryotic chromosome protected from broken chromosome repair mechanisms?
Telomere binding proteins protect the ends of the chromosome from mechanisms that repair broken chromosomes.
Is telomerase active in most cells?
NO. Telomerase is not active in most cells.
What is the consequence of telomerase being inactive in most cells?
Telomeres shorten as a cell replicates.
Once telomeres are too short, the cell dies.
This is a “clock” that counts down allowable divisions!
What kinds of cells have active telomerase?
Many kinds of cancer cells have active telomerase.
What is the consequence of active telomerase in cancer cells?
As the tumor cells replicate, their telomeres elongate.
This impedes cell death leading to immortalization!
