DNA Replication Flashcards
DNA of different molecular weights are separated using the following method?
Cesium chloride density gradient centrifugation
What model of DNA is the correct model?
Semi-conservative model. Each daughter contains one parental and one daughter strand
Which enzyme catalyzes the formation of a phosphodiester bond between the 3’ hydroxyl group or one nucleotide and the 5’ phosphate of an adjacent one?
DNA-dependent DNA-polymerase
In the nucleotide addition reaction by DNA polymerase, the 2’-hydroxyl attacks the alpha phosphate from the adjacent nucleotide. T/F?
False
What direction are chains synthesized?
5’ –> 3’
Where does DNA copying start?
At origin of replication
Does DNA replication start in more than one place?
In bacterial cells no, in eukaryotic cells YES (10,000+ in humans). Starts at replication origins. Ends at terminus of replication.
Does DNA replication go in one direction or in two directions?
Bidirectional so 2
Does bidirectional DNA replication proceed continuously?
One strand is continuous (leading), the other is discontinuous (lagging). The lagging strands are OKAZAKI fragments.
What are autonomously replicating sequences (ARS)?
Multiple origins of replications. Multiple origins means less characterized (eukaryotes).
What enzymes are involved in bacteria replication?
DnaA- binds 9-mer sequences, bends DNA, breaks hydrogen bonds
DnaB- helicase that uses ATP to break hydrogen bonds of complementary bases to separate strands and unwind helix
DnaC- carries DnaB to helix
What enzymes are required only for initiation of bacterial replication?
DnaA and DnaC
What enzyme is required throughout process of replication?
DnaB, SSB, and topoisomerases
What else is needed for DNA replication?
A primer created by PRIMASE an RNA polymerase
DNA dependent DNA polymerase I function
Repairs enzymes and excise and replace mismatch nucleotides (fill gaps).
DNA dependent DNA polymerase II function
Repairs enzymes
DNA dependent DNA polymerase III function
Major DNA replicase involved in replicating bacterial genome
DNA dependent DNA polymerase IV and V
Primarily repair functions in SOS response (major DNA damage)
What is a holoenzyme?
Multiprotein complex in which a core enzyme is associated with the additional components needed for full function
How many copies of DNA Pol III are in the replisome?
2 (sometimes 3) at each replication fork. 1 copy elongates in same progression as fork progression (leading strand) and one elongates discontinuously in opposing direction (lagging strand).
Activities of DNA polymerase I?
- 5’-3’ exonuclease activity that removes RNA primers.
- 5’-3’ polymerase activity that adds DNA nucleotides to 3’ end of DNA segment
What enzyme seals the gap between DNA segments?
DNA ligase
How many protein subunits are included in DNA polymerase III holoenzyme?
11 including 2 Pol III core polymerases
What is DNA proofreading?
Correct occasional errors that occur because tautomers pair with the wrong patterns.
What are tautomers?
DNA nucleotide bases that convert to alternative structures. Different base pairing preferences. MOST COMMON FORM OF REPLICATION ERROR
What happens to a mismatched base pair on a daughter strand?
Displaced into the 3’-to-5’ exonuclease site of the enzyme. 3’ end returns to polymerase active site and incorporation of new nucleotides resumes.
Steps:
- separate strands
- add RNA primers
- polymerize DNA from RNA
- remove RNA primers
- Fill in the gaps by extending DNA from 5’ ends
What are telomeres?
Repetitive sequences at the end of chromosomes that ensure incomplete chromosome replication does not affect vital genes. Synthesized by telomerase.
Telomerase parts
- RNA= template for copying to synthesize the DNA telomere sequences
- Protein part
What kind of polymerase is telomerase?
RNA-directed DNA-polymerase
Steps of telomerase:
- uses it’s RNA component to synthesize complementary DNA in short bursts
- DNA polymerase completes the lagging strand
What is the relationship between telomeres, aging and cancer?
Chromosome stability, cell longevity, and reproductive success. active in germ-line cells and some stem cells
What happens to reactivation of telomerase?
Lead to aging cells that continue to proliferate
During DNA replication, the following strands are synthesized/extended in the 5’ to 3’ direction?
Both leading and lagging
Which activity of the DNA pol I is used for RNA primer removal in prokaryotes?
5’-3’ exonuclease
