chapter 6 Flashcards
The process of DNA synthesis is begun by _ that bind to specific DNA sequences called replication origins.
initiator proteins
DNA polymerase is so accurate that it makes only about one error in every _ nucleotide pairs it copies.
10^7
when DNA polymerase does make a rare mistake and adds the wrong nucleotide, it can correct the error through an activity called _.
proofreading
proofreading mechanism is possible only for DNA polymerases that synthesize DNA exclusively in the _ direction, otherwise, it would be _
5’-to-3’
unable to proofread
when a nucleotide is removed from the 5’ end, the remaining strand lacks the necessary chemical group (-_) on the 5’ end for the next nucleotide to be added. Without this group, the polymerase _, so the process is blocked, making it a _ for further synthesis.
OH
can’t continue building the DNA
dead end
Thus, for a DNA polymerase to function as a self-correcting enzyme that removes its own polymerization errors as it moves along the DNA, it must proceed only in the _ direction.
5’-to-3’
An _ fragment thus serves as a _ for DNA synthesis, and the enzyme that synthesizes the RNA primer is known as _.
RNA
primer
primase
Enzymes called DNA _ relieve this ten- sion. A DNA _ produces a transient, single-strand _ in the DNA backbone, which temporarily releases the built-up tension; the enzyme then reseals the _ before falling off the DNA
topoisomerases
topoisomerase
nick
nick
purine bases (_)
A and G
The rep- lication machine makes approximately one mistake per 10^7 nucleotides synthesized; DNA mismatch repair corrects 99% of these replication errors, increasing the overall accuracy to one mistake in _ nucleotides synthesized.
10^9
a _ is especially difficult to repair.
double-strand break
double-strand break can be repaired by:
nonhomologous end joining
homologous recombination
Homologous recombination most often occurs _ before _
shortly after a cell’s DNA has been replicated
cell division
Before a cell divides, it must _.
accurately replicate the vast quantity of genetic information carried in its DNA
Because the two strands of a DNA double helix are _, each strand can act as a _ for the synthesis of the other. Thus DNA replication produces _, double-helical DNA molecules, enabling genetic information to be copied and passed on from a cell to its _ and from a parent to its _.
complementary
template
two identical
daughter cells
offspring
During replication, the two strands of a DNA double helix are _ at a _ to form two _. DNA _ at each fork produce a new, _ DNA strand on each _.
pulled apart
replication origin
Y-shaped replication forks
polymerases
complementary
parental strand
DNA polymerase replicates a DNA template with remarkable _, making only about one error in every _ nucleotides copied. This accuracy is made possible, in part, by a _ process in which the enzyme _.
fidelity
_
10^7
_
proofreading
_
corrects its own mistakes as it moves along the DNA
Because DNA polymerase synthesizes new DNA in the _, only the _ at the _ can be synthesized in a _ fashion. On the _, DNA is synthesized in a _ process, producing _ that are later joined together by _.
5’-to-3’ direction
leading strand
replication fork
continuous
lagging strand
discontinuous backstitching
short fragments of DNA (Okazaki fragments)
DNA ligase
DNA polymerase is _ of starting a new DNA strand from scratch. Instead, DNA synthesis is _ called _, which makes short lengths of _ that are then elongated by _. These _ are subsequently _ and _.
incapable
primed by an RNA polymerase
primase
RNA primers
DNA polymerase
primers
removed
replaced with DNA
DNA replication requires the _ that form a _ that _ the double helix and _ the information contained in both DNA strands.
cooperation of many proteins
multienzyme replication machine
pries open
copies
In eukaryotes, a special enzyme called _ replicates the DNA at the ends of the chromosomes, particularly in rapidly dividing cells.
telomerase
The rare copying mistakes that escape _ are dealt with by _, which increase the accuracy of DNA replication to one mistake per _ nucleotides copied.
proofreading
mismatch repair proteins
10^9
Damage to one of the two DNA strands, caused by _, is repaired by a variety of _ that _ damaged DNA and _. The _ DNA is then resynthesized by a _, using the _ as a template.
unavoidable chemical reactions
DNA repair enzymes
recognize
excise a short stretch of the damaged strand
missing
repair DNA polymerase
undamaged strand
If both DNA strands are broken, the double-strand break can be rapidly repaired by nonhomologous end joining. Nucleotides are _, _.
often lost in the process
altering the DNA sequence at the repair site
