Chapter 6 Flashcards
(56 cards)
when does DNA replication occur?
before a cell can produce two genetically identical daughter cells
what do replication initiator proteins do?
recognize sequences of DNA at replication origins and pry apart the two strand of double helix
the exposed single strand can serve as what for copying DNA?
templates
replication forks move in what direction?
move away in opposite directions from multiple replications origins in eukaryotic chromosome
what direction is DNA synthesized?
5’ to 3’
the addition of what to the 3’-hydroxyl end of a polynucleotide chain is the fundamental reaction by which DNA is synthesized?
deoxyribonucleotide
the nucleotides enter the reaction as ______
nucleoside triphosphates
what does DNA polymerase do?
catalyzes the addition of nucleotides to the free 3’ hydroxyl on the growing DNA strand
what does the breakage of a phosphoanhydride bond in the incoming nucleoside triphosphate do?
release a large amount of free energy and thus provides the energy for the polymerization reaction
at the replication fork, the two new synthesized DNA strands are of _____
opposite polarities
the lagging strand of DNA must be made initially as……
a series of short DNA strands called Okazaki fragments that are later joined together
the DNA strand that is synthesized discontinuously is called?
the lagging strand
the DNA strand that is synthesized continuously is called?
the leading strand
can DNA polymerase proofread its own work?
yes
if an incorrect nucleotide is added to a growing strand, the DNA polymerase will do what?
cleave it from the strand and replace it with the correct nucleotide before continuing
true or false? DNA polymerase contains separate sites for DNA synthesis and proofreading?
true
why does proofreading explain why DNAs are synthesized in 5’ to 3’ direction?
growth in 5’ to 3’ direction allows chain to continue to be elongated when incorrect nucleotide has been added then removed
how is RNA primers made?
at intervals of about 200 nucleotides on lagging strand by primase
how long are RNA primers
10 nucleotides long
how are primers removed?
by nucleases that recognize an RNA strand in and RNA/DNA helix and degrade it
removing a primer leaves a gap, how is it filled?
filled by a DNA repair polymerase that can proofread as it fills in the gaps
how are the completed fragments joined together?
by DNA ligase
what does DNA ligase do?
catalyze the formation of phosphodiester bond between 3’ OH end of fragment and 5’ phosphate end of the next-linking up sugar phosphate backbone
where are DNA polymerase located when DNA is replicating?
one on leading strand and other on lagging strand
