DNA Replication, Repair and Recombination Flashcards
(18 cards)
Which of the models held that the two parental strands would remain associated after replication?
conservative
The conservative model of replication posited that after replication of the parental strands, the original parental molecule remained intact. In this model, the two newly replicated strands would associate, forming their own new molecule.
What is the name of the DNA sequence where replication begins?
replication origin
DNA synthesis begins at replication origins, where local strand separation is promoted by initiator proteins.
The sequence at which DNA replication begins tends to have which characteristic?
AT-rich
Replication origins tend to be very rich in A-T base pairs to facilitate local strand separation by initiator proteins.
In which direction, and on which strands does DNA replication proceed from a replication origin on a chromosome?
in both directions, on both strands
The DNA replication machinery can only add nucleotides in the 5′ to 3′ direction, but both strands are replicated using a clever workaround by the cell. In addition, replication forks move in both directions from a replication origin.
The bonds that link two DNA strands together are
hydrogen bonds.
Two DNA strands are held together by many weak noncovalent hydrogen bonds between complementary base pairs.
The energy for the polymerization reaction in DNA synthesis is powered by
the breaking of high-energy phosphate bonds in the deoxynucleotides.
Formation of the phosphodiester bonds requires input of energy. This is provided by the hydrolysis of the high-energy phosphoanhydride bonds in the incoming nucleotide triphosphates that are the building blocks for the DNA polymer.
How does Polymerase help maintain the accuracy of DNA replication?
DNA polymerase can cut out improperly base-paired nucleotides and add the correct one during synthesis.
Concurrent with the polymerization reaction, polymerase double checks the base pair that it just formed and, if it is incorrect, it will snip it out. Then the right base will be added to form a correct base pair.
How are the primers from which DNA synthesis starts different from the DNA itself?
The primers are made up of RNA not DNA.
RNA primers are made by an enzyme called primase to provide a “seed” from which the DNA polymer can grow. The primer provides a base paired 3′−OH for starting the reaction.
What is the name of the enzyme that fills the sequence gaps after primers are removed from a newly synthesized DNA strand?
repair polymerase
After a nuclease removes the primers, there are gaps in the DNA molecule. A repair polymerase can come in and fill the gaps to produce a continuous strand.
What is the name of the protein that binds the two separated DNA strands to keep them from base pairing again before they can be replicated?
single-strand binding protein
As a replication fork travels along the chromosome, the helicase pries apart the two strands of the double-helix. Single-strand binding protein holds these two strands apart and keeps them from reforming base pairs by binding to the single-stranded DNA.
What is the function of a topoisomerase in DNA replication?
It relieves the tension in DNA strands.
Unwinding of the DNA by helicase produces tension in the DNA molecule because the DNA cannot freely rotate. Topoisomerases cut the DNA to allow the DNA to freely rotate and relieve this tension, avoiding supercoils and tangles, and then reseals the DNA.
Which strand will telomerase elongate?
the template of lagging strand
Telomerase extends telomere repeat sequences at the end of chromosomes by extending the template of the lagging strand. The incomplete lagging strand will be extended by polymerase, using the extended template.
What is the name of the type of damage caused by an improperly paired base in the DNA?
mismatch
Sometimes mispaired bases escape the proofreading of DNA polymerase during replication. These are called mismatches and can be repaired after replication is complete.
What is the first step that must occur to repair damage on one strand of the double helix?
The damaged region must be removed.
Repair of damaged bases occurs through three steps. The first step is to remove the damaged base and the neighboring bases. Then, the gap can be filled using the undamaged strand as a template and the backbone sealed by ligase.
In bacteria, how does the cell recognize which strand is the newly synthesized strand and thus contains the mismatch?
The newly synthesized strand is unmethylated.
In bacterial DNA, adenine bases are methylated. This occurs slowly, so newly synthesized strands remain unmethylated for a time after replication and gives mismatch repair enzymes time to recognize the damaged strand.
Which double-strand break repair mechanism is a simple ligation mechanism?
nonhomologous end joining
Nonhomologous end joining is a mechanism for sealing DNA double-strand breaks using DNA ligase. Homologous recombination is more complicated, with end processing and copying of the damaged region from an intact copy of that sequence.
DNA replicatie wordt als semi-conservatief beschouwd, omdat…
elk dochter DNA molecuul uit één streng van het ouderlijke DNA Molecuul bestaat en één nieuwe streng d. nieuwe DNA strengen
DNA polymerase katalyseert de binding van een nucleotide aan de groeiende DNA streng. Wat voorkomt dat dit enzym de omgekeerde reactie gaat katalyseren?
Hydrolyse van PPi naar Pi + Pi
