Chapter 6: DNA Replication and Repair Flashcards
Each strand of DNA can serve as a _________, for the synthesis of a new complementary strand.
template, or mold
Because each parental strand serves as the tem- plate for one new strand, each of the daughter DNA double helices ends up with one of the original (old) strands plus one strand that is completely new; this style of replication is said to be ___________.
semiconservative
the two DNA strands are locked together firmly by the large numbers of __________ between the bases on both strands
hydrogen bonds
The process of DNA synthesis is begun by initiator proteins that bind to specific DNA sequences called __________.
replication origins
DNA molecules in the process of being replicated contain Y-shaped junctions called ______.
replication forks
The two forks move away from the origin in opposite directions, unzipping the DNA double helix and copying the DNA as they go. DNA replication—in both bacterial and eukaryotic chromosomes—is therefore termed __________.
bidirectional
The movement of a replication fork is driven by the action of the replication machine, at the heart of which is an enzyme called ________.
DNA polymerase
This enzyme catalyzes the addition of nucleotides to the 3ʹ end of a grow- ing DNA strand, using one of the original, parental DNA strands as a template
DNA polymerase
The polymerization reaction involves the formation of a phosphodiester bond between the 3ʹ end of the growing DNA chain and the 5ʹ-phosphate group of the incoming nucleotide, which enters the reaction as a __________.
deoxyribonucleoside triphosphate
small DNA pieces
Okazaki fragments
The DNA strand that is made discontinuously in this way is called the ________.
lagging strand
the other strand, which is synthesized continuously, is called the __________.
leading strand
when DNA polymerase does make a rare mistake and adds the wrong nucleotide, it can correct the error through an activity called _____.
proofreading
takes place at the same time as DNA synthesis.
proofreading
This proofreading mechanism is possible only for DNA polymerases that synthesize DNA exclusively in the _______ direction.
5ʹ-to-3ʹ
RNA fragment serves as a _____ for DNA synthesis, and the enzyme that synthesizes the RNA primer is known as ________.
primer; primase
an enzyme that synthesizes RNA using DNA as a template.
primase
A nuclease degrades the RNA primer, a DNA polymerase called a _______ replaces the RNA primers with DNA and the enzyme ____ joins the 5ʹ-phosphate end of one DNA fragment to the adjacent 3ʹ-hydroxyl end of the next
repair polymerase
DNA ligase
For DNA replication to occur, the double helix must be continuously pried apart so that the incoming nucleoside triphosphates can form base pairs with each template strand. Two types of replication proteins—________________—cooperate to carry out this task.
DNA helicases and single-strand DNA-binding proteins
produces a transient, single-strand nick in the DNA backbone, which temporarily releases the built-up tension; the enzyme then reseals the nick before falling off the DNA
DNA topoisomerase
Back at the replication fork, an additional protein, called a ________, keeps DNA polymerase firmly attached to the template while it is synthesizing new strands of DNA.
sliding clamp
hydrolyzes ATP each time it locks a sliding clamp around a newly formed DNA double helix
clamp loader
Most DNA damage is only temporary, because it is immediately corrected by processes collectively called_______.
DNA repair
loss of purine bases
depurination
spontaneous loss of an amino group from a cytosine in DNA to produce the base uracil
deamination
