DNA replication 1 Flashcards
how many hydrogen bonds are in A:T and G:C respectively
A:T - 2 Hydrogen bonds. G:C - 3 hydrogen bonds
what is the equation for the linking number
linking number = twist + writhe
how do you calculate twist and writhe
twist = DNA size divided by 10, writhe = number of times double helix passses over itself
what is the two states of circular DNA
Relaxed and supercoiled
what is the two states of supercoiled DNA
Positive and Negative
what does negative supercoiling do
facilitates DNA strand separation
what does positive supercoiling do
inhibits DNA strand separation
when are DNA strands separated
during replication and transcription
what alters the tension of supercoiling?
topoisomerase 1/2 and DNA gyrase with ATP.
what is the main difference between topoisomerase 1 and 2?
topoisomerase 1 nicks a single strand to pass the other strand through gap before resealing it. topoisomerase 2 nicks the two strands and pass through the duplex gap before resealing nick
is DNA gyrase energy dependent ?
yes
does positive supercoiling require energy
yes
does negative supercoiling require energy
yes
what are the two steps of replication strategy
1 converts ssDNA circle to dsDNA circle 2 initiate rolling circle replication
what is the oriC ?
where DNA replication is recognised and bound by initiator proteins
what is an initiator protein ?
a protein which is responsible for recruiting more proteins to begin replication
what direction does the OriC go in?
bidirectionally with two forks
what do you call the end point of the oriC
the terminus
what are the 3 steps of the polymerase mechanism?
- substrate binding. 2.nucleotide incorporation 3. translocation
what are the 3 core complexes of subunits
alpha, beta and omega
what does the alpha subunit do
DNA polymerizing activity
what does the beta subunit do
3’-5’ exonuclease
what does the omega subunit do
stimulates beta
what is the sliding clamp loader complex?
a protein complex that prevents DNA polymerase falling off during replication and loads itself onto DNA during replication
give the 5 steps of the sliding clamp loader complex
1 clamp binds to DNA polymerase and ATP 2 complex opens clamp, places on DNA. 3 hydrolyses ATP releases energy closes clamp around DNA 4 DNA polymerase binds to clamp 5 DNA synthesis begins
is the sliding clamp loader complex semi conservative?
yes
can the sliding clamp loader complex synthesize DNA de novo?
no
what is each strand used as a template for in sliding clamp loader complex
synthesis of a new strand
are the two strands parallel or anti parallel?
anti parallel
what is an okazaki fragment
short, newly synthesized DNA fragments strand that is synthesized on the lagging strand during DNA replication
what is the lagging strand
the strand of DNA synthesized in the opposite direction of the replication fork movement
what is DNA A
an initiator protein
what is DNA B
replicative helicase- separates the two DNA strands. Located on the lagging strand
what is DNA G
DNA primase - synthesizes new okazaki fragments
what is SSB
single stranded DNA binding protein that always coats ssDNA, confers rigidity
what is the ORC
The origin recognition complex (ORC) is a multi-subunit protein complex that recognizes and binds to the origin of replication on DNA to initiate DNA replication.
