DNA Replication Preview Flashcards
What is the Direction of DNA replication?
Unidirectional: replication growth at two starting points
Unidirectional growth of double strands from 1 starting point
Bidirectional growth at one starting point
Where Does DNA replication begin
For DNA, replication begins at specific places that is easy for initiator proteins to bind to and then replication forks bind to keep the strands separated
What happens at replication forks
Replication fork is asymmetrical and the leading strand is continuously replicate DNA and lagging strand discontinuously replicates DNA
What is a simplified process of DNA replication
- Separate strands
- Synthesize
- Proofread
What function does initiator proteins have DNA replication for bacteria?
Initiator proteins bind to origin of replication
helps DNA helicase (catalyzes and breaks hydrogen bond of strands
What unwinds DNA?
DNA helicase binds to origin and reads the strands from a 5’ to 3’ on the lagging strand
What follows DNA helicase
Single strand binding proteins that keep the strands separated
Primase
makes the rna primer
RNA primer
Short sequence of RNA complementary to the template strand
In which direction does primase move
It reads the template strand in the 3’ -5’ direction
Describe the process and function of primase
Following single strand building proteins, primase attaches to the template strand and moves in a 3’-5’ direction. While it moves, incoming nucleotides are brought in and primase joins them together and eventually the primase will make rna primer
DNA polymerase
After RNA primers do the job of placing nucleotides, DNA polymerase comes in and start synthesizing new copies of DNA and adds on 3’ end
Helper of DNA polymerase
DNA polymerase needs help sticking on DNA strand and a sliding clamp comes and does this job
How are the Okazaki fragments on the lagging strand linked
Ligand seals the nick by using ATP to attach 2 phosphates and then AMP is released
The unwinding problem
When helicase is unwinding the DNA strand there is a lot of tension that creates circular shapes, topoisomeres fixes that
Shortening on the 5’ end
This is a problem for the lagging strand because the primase doesn’t do a good job of putting a primer on the very end so there is sequence information missing.
This happens because when the primer is removed DNA polymerase does not add onto the 5’ end
What is the solution to the shortening
Telomere has RNA template and through reverse transcriptase (RNA—DNA), DNA is added onto the new strand to and after the telomere is removed there will still be a gap but it doesn’t matter because it is all repeated sequences
3’-5’ exonuclease
Removes disincorporated nucleotides
What are the two sites present on DNA polymerase
It has a polymerizing site and editing site
Strand-directed mismatch repair
When a newly synthesized DNA strand has an error, there are two enzyme involved in fixing this problem
First there is MUTs, this recognized the messed up geometry and MUTL looks for the nick to fix the problem and removes the mismatch so DNA synthesis can put in the proper match
How can DNA be damaged
Radiation, Oxidation, heat, chemicals
How can radiation lead to alterations in DNA
Catalyzes two covalent bonds between pyrimidines, making a pyrimidine dimer
Fill in the blank. There can also be spontaneous damage to DNA by _________ and __________
Depurination (Loss of adenine/guanine) and deamination (cytosine into uracil)
What are the two mechanisms for DNA repair
BER (base excision repair): removes the uracil and places the appropriate cytosine
NER(nucleotide excision repair): removes a large section of sequence and DNA ligase and polymerase puts in the appropriate sequence
