ch 6 Flashcards
who discovered that DNA was replicated semi conservatively
Meselson and Stahl
label
red: replication forks
green: replication origin
purple: template DNA
blue: newly synthesized DNA
what opens the DNA double helix for the start of DNA replication
initiator proteins
describe image
multiple origins of replication are opening and meeting as they replicate
DNA polymerase can only add nucleotides to the
3’ end of the strand of DNA
how fast do DNA replication forks go in bacteria vs humans
bacteria: 1000 nucleotide pairs per sec
humans: 100 nucleotide pairs per sec
what does DNA polymerase do
this enzyme catalyzes the addition of nucleotides to 3’ end of DNA
what is the leading strand of DNA
the strand of DNA that is replicated continuously
what is the lagging strand of DNA
the strand of DNA that is made discontinuously
what are okasaki fragments
small DNA pieces added to the lagging strand
what supplies the energy for a nucleotide to be added to the DNA strand
the incoming nucleoside triphosphate
how many phosphates must break off the incoming nucleoside triphosphate to attach to the DNA strand
2
the template strand will always be
3’ - 5’
what is primase and what does it do
- produces an RNA “primer” that is complementary to the template DNA strand
- DNA polymerase builds onto the primer
- RNA primer is later removed and replaced with DNA
understand
okay
about how often does DNA polymerase make a mistake
every 10^7 nucleotide pairs it copies
understand
okay
what does DNA polymerase do to proofread
it checks to make sure if the right base was added before it moves on, if the wrong one was added it clips it off and tries again
what replaces the RNA primers with DNA
repair polymerase
what does DNA ligase do
joins the 5’ phosphate end of one DNA fragment to the adjacent 3’ hydroxyl end of the next (closes any gaps)
why do primers made of RNA frequently contain mistakes
because they are made of RNA they cant proofread
what does helicase do? what problems does it cause
it prys open the double helix of DNA, but the DNA ahead of the split gets wound very tightly
what does DNA topoisomerase do
relieves the pressure caused by helicase by creating a transient single strand nick in the DNA backbone which temporarily releases tension. the enzyme then reseals the nick before falling off the DNA
what does the sliding clamp protein do
keep DNA polymerase firmly attached to the template while it synthesizes new DNA
