DNA synthesis Flashcards
The site at which replication occurs is called the _______
replication fork
Each of the two parental strands of DNA serve as a template for the synthesis of a ______
complementary strand
_______ and ________ are required to unwind the DNA helix of the parental strands
Helicases and Topoisomerases
________ is the major enzyme involved in repilcation. It’s function is to……
DNA polymerase: copies parental/template strands in the 3’ to 5’ direction, producing new strands in the 5’ to 3’ direction
DNA polymerase requires a …..(think primers…)
3’ Hydroxyl group of the primer.
***primer synthesized by primase (RNA primer)
The precursors for replication are ______
deoxyribonucleotide triphosphates (sugar, base, phosphates)
DNA synthesis proceeds in the _______ direction meaning that….
5’ to 3’ –> one strand continuously, other discontinuously creating small fragments because DNA must synthesize in the 5’ to 3’ direction
Replication is semiconservative, meaning…
each daughter chromosome contains one parental and one new
With the addition of a new deoxyribonucloside triphosphate (NUCLEOTIDE) via a phosphodiester bond a ________ is released. Why is this important?
pyrophosphate (PPi)—-The deltaG of PPi = -30KJ which drives the reaction forward. Energetically favorable.
Prokaryotes->Initiation of DNA replication (circular ds) starts at _________
binding protein DnaA
**at a Single point of origin, OriC
P-> synthesis begins at OriC and occurs at two ….. that move away from the origin ________
two asymmetrical Y-shaped rep forks–> bidirectionally
P–> replication ends at ______
termination point on opposite side of circular chromosome
** multiple rounds occurring at same time
P-Major initiator protein is ________
DnaA
P-Helicases (______) separate DNA strands and unwind parental duplex
DnaB
P-________ prevent the strands from re-associating and protects strand from cleaving proteins
single-stranded binding proteins
P-_______ are enzymes that can break phosphodiester bonds and rejoin them to relive the supercoiling tension caused by unwinding
topoisomerases
**DNA GYRASE in bacteria
On leading strand DNA poly moves ______ on the template creating new strand in ______ direction—-> CONTINUOUS
3’ to 5’ on template
new strand 5’ to 3’
On the lagging strand _______ are created in the _______ direction
Okazaki Fragments; 5’ to 3’
*fragments ligated together
Why? Because daughter strands can ONLY be made in the 5’ to 3’ direction so there must be a lagging strand
On the lagging strand there are multiple ______ and after DNA poly adds to it the ______fragments are produced that are ligated together by ______
RNA primers; Okazaki fragments; Ligase
DNA poly can’t lay down without _____ from RNA primer/ DNA primase
3’ Hydroxyl
Clamp proteins prevent….
DNA poly from falling off template strand
Polymerases typically have a ______function that….(important for errors)
proofreading function detecting/correcting incorrect bases
RNA primers are removed from Okazaki fragments by ______ and RNAase H. It then fills in gaps left from the removal and ______joins in to join the two chains together
Poly I ; DNA ligase
Pol I —> (think Okazaki)
Pol II—>
Pol III —>
I–> fill in gaps, remove RNA primer, DNA repair
II–> DNA repair
III –> DNA REPLICATION
DNA synth is similar in eukaryotes but with more proteins and the complication of having to replicate through _______. Different regions of chromosomes replicate at different times in cell cycle (S phase) unlike Prokaryotes that replicate continuously.
nucleosomes
Unlike prokaryotes, eukaryotes have multiple….. which appear as bubbles
multiple points of origin of rep
Eukaryotes have 15 different polymerases; Poly-___ is the major replicative enzyme
Poly Delta
Topoisomerase I –> enzyme that transiently forms a single covalent bond with DNA to allow free rotation of DNA. Think of this as the “_____” reaction of a SINGLE strand
Nicking
Topoisomerase II —> Think of this one as the ______ because it breaks BOTH strands and fixes the break
Magic Rope trick
**increased expression in Cancer cells–> anticancer drug target
End of replication problem…..
How to fix it?
after replication the lagging strand cannot be finished resulting in a 3’ overhang–> TELOMERASE uses RNA primer to lengthen 3’ strand
Telomerase adds a short piece of DNA, a ______, that is lost when a cell divides and DNA is replicated
telomere
Telomerase is an example of _______ because….
Reverse Transcriptase because it crease a ssDNA from an RNA template
Telomerase with bound RNA template adds DNA nucleotides to _____strand to allow DNA polymerase to complete the lagging strand
Parental Strand (leading strand)
What type of cells produce lots of telomerase?
Little amounts?
embryonic cells to allow them to indefinitely divide
Somatic express little, decreasing with time
_____cells upregulate telomerase.Therefore making it a drug target.
Cancer Cells
