DNA Replication Flashcards
________ is circular and has only one chromosome
Bacterial DNA
_____ occurs in both directions of a chromosome
Replication
Example of prokaryotic DNA replication
E-coli (circular chromosome)
has 5M base pairs an tkes less than 1 hour to replicate
What are the 3 phases of DNA replication?
initiation
elongation
termination
What happens in the initiation phase?
Replication begins at an origin of replication
What happens in the elongation phase?
New strands of DNA are synthesized
What happens in the termination step?
Replication is terminated at the termination site
What is the difference between bacteria and eukaryotes in the initiation step?
Bacteria: 1 origin of replication
Eukaryotes: hundreds or thousands of origin replications
The replication proceeds in ___ directions.
2
A Y shaped region where the new strands are elongating
replication fork
What is a replication fork?
Y shaped region where the new strands are elongating
What is primer made of?
RNA nucleotides
What happens after the generation of the primer?
DNA Polymerase III will elongate the chain
What is the fonction of DNA polymerase I?
Proof read, repairs, replaces
______ is a specific sequence of nucleotides (A and T rich) on DNA
Origin of Replication
________initiate replication by identifying origin of replication sequence (AT’s), then attach to DNA
Enzymes
The double helix is unwound by the enzyme ____
Helicase
________ prevent DNA from winding up
Single-stranded binding proteins
_____ relieves torque created by the helicase
DNA Gyrase
_____ is a DNA replicating structure made up of protein clamps and enzymes which binds at the replication fork.
replisome
The replisome consists of 2 things…
- primase
2. helicase
_____ makes an RNA primer to which new nucleotides will be added
Primase
What happens during elongation?
Primase makes RNA primer
DNA pol III adds new nucleotides in synthesis step
______ is responsible for the majority of DNA synthesis
DNA polymerase III
What are the 2 DNA pol III restrictions?
- only add nucleotides to the 3’ end of DNA
2. only add nucleotides to an existing nucleotide
What are the 2 steps in termination?
DNA Pol I removes RNA primer and fills gaps with DNA nuculeotides
DNA ligase seals the gap by forming a phosphodiester bond
______ removes the RNA primer and fills the gaps with DNA nucleotides
DNA Pol I
______ seals the gap by forming a phosphodiester bond
DNA ligase
________ is semi-discontinuous
DNA replication
is synthesized continuously (in the same direction as the replication fork)
leading strand
______ is synthesized discontinuously creating Okazaki fragments
Lagging strand
2 reasons why it is semi-discontinuous
DNA Pol III can only add nucleotides to the 3’ end of the newly synthesized strand
DNA strands run anti-parallel to each other
________ moves in 1 direction, synthesizing both strands simultaneously
The replication fork
Human has ________ and it takes few hours to copy
6 billion base pairs
What is the problem existing in synthesizing the ends of the chromosomes?
Lack of a primer on the 5’ end
With each round of DNA replication, the linear eukaryotic chromosome becomes ____.
shorter
______ are repeated DNA sequence on the ends of eukaryotic chromosome.
Telomeres
What is the enzyme producing telomeres?
Telomerase
contains an RNA region that is used as a template so a DNA can be produced
Telomerase
DNA can be damaged by chemical or physical agents called
Mutagens
Name a specific DNA repair mechanism
thymine dimers
Name a non-specific DNA repair mechanism
excision repair
DNA polymerase can only go from the __’ to the __’
5’ to 3’
