20.3 - DNA replication Flashcards
The product of this mechanism would be a new DNA molecule in which one strand is the ________-, strand and the second strand is a ____ synthesized, or ____, strand.
parent/original
newly
daughter
This mode of DNA replication is called
semiconservative replication
In semiconservative DNA replication, each parent strand serves as a
template for the synthesis of a new daughter strand.
Bacterial chromosomes are __________ ranging in size from 600,000 to 10,000,000 base pairs.
circular molecules of DNA
DNA replication begins at a unique sequence on the circular chromosome known as the
replication origin
Replication occurs ______ at the rate of about ________
bidirectionally
500 new nucleotides every second
The point at which the new deoxyribonucleotide is added to the growing daughter strand is called the
replication fork
It is here that the DNA has been ____ to allow binding of the various proteins and enzymes responsible for ________-
opened
DNA replication
Since DNA synthesis occurs bidirectionally, there are ________-moving in ______ directions.
two replication forks
opposite
Replication is complete when the replication forks ____ approximately ____around the circular chromosome.
collide
halfway
The first step in DNA replication is the
seperation of the DNA strands
The protein _____ does this by breaking the _____ between the_____-
helicase
hydrogen bonds
base pairs
breaking the h bonds between the base pairs causes
supercoiling of the molecule.
This stress is relieved by the enzyme
topoisomerase
topoisomerase
travels along the DNA ahead of the replication fork.
___________ binds to the separated strands, preventing them from coming back together.
single-strand binding protein
In the next step, the enzyme ___ catalyzes the synthesis of a small piece of ____ (ten to twelve nucleotides) called an RNA ___ that serves to “prime” the process of DNA replication.
primase
RNA
primer
Now the enzyme _________“reads” each parental strand, also called the ____, and catalyzes the polymerization of a complementary ____ strand.
DNA polymerase III
template
daughter
what are the precursors for DNA replication
Deoxyribonucleotide triphosphate molecules
In this reaction, a _______group is released as a phosphoester bond is formed between the ___________ of the nucleotide being added to the chain and the ____ of the nucleotide on the daughter strand. This is called 5′ to 3′ synthesis.
pyrophosphate
5′-phosphoryl group
3′-OH
Because the two strands of DNA are antiparallel and DNA polymerase can only catalyze 5′ → 3′ replication, only one of the two DNA strands (top strand) can be read continuously to produce a daughter strand. what about the other strand
must be synthesized in segments that are extended away from the direction of movement of the replication fork (bottom strand).
These discontinuous segments are later covalently joined together by DNA ligase.
DNA polymerase III can only catalyze DNA chain elongation in the
5′ to 3′ direction
One strand, called the ____ strand, is replicated continuously. The opposite strand, called the ____ strand, is replicated discontinuously.
leading
lagging
For the leading strand, a single ____ is produced at the replication origin and ______ continuously catalyzes the addition of nucleotides in the _______, beginning with addition of the ____ nucleotide to the _____.
RNA primer DNA polymerase III 5′ to 3′ direction first RNA primer
On the lagging strand, _____ are produced as the replication fork proceeds along the molecule.
many RNA primers
in the lagging strand DNA polymerase III catalyzes DNA chain elongation
from each of these primers
in the lagging strand When the new strand “bumps” into a previous one, synthesis
stops at that site
in the lagging strand
Meanwhile, at the replication fork, a new ___is being synthesized by ____
primer
primase
The final steps of synthesis on the lagging strand involve
removal of the primers
repair of the gaps
sealing of the fragments into an intact strand of DNA
The enzyme DNA polymerase I catalyzes the removal of the _______ and its replacement with _____-
RNA primer
DNA nucleotides
In the final step of the process, the enzyme DNA ligase catalyzes the formation of a
phosphoester bond between the two adjacent fragments.
In addition to catalyzing the replication of new DNA, DNA polymerase III is able to ______________
If the wrong nucleotide has been added to the growing DNA strand, it is ___________
proofread the newly synthesized strand.
removed and replaced by the correct one
Eukaryotic DNA Replication
DNA replication begins at many replication origins and proceeds bidirectionally along each chromosome.
