L14 - DNA replication & transcription

what did the Messelson and Stahl Experiment suggest?

that each strand can serve as a template for the synthesis of a new strand

What are the 3 models that potentially explained DNA replication? (Messelson and Stahl Experiment)

conservative, dispursive, and semi-conservative

how does the conservative model explain the DNA replication process?

the entire dna molecule serves as a template for a whole new dna molecule

how does the dispursive model explain the DNA replication process?

both nucleotide strands break down (disperse) into fragments and then somehow resemble two 2 complete dna molecules

how does the semi-conservative model explain the DNA replication process?

two nucleotide strands of dna separate and each serves as a template of the synthesis of a new strand.

what are the requirements for replication?

dna template, substrate, enzymes and proteins that assemble substrates intro a new DNA molecule

what are nucleotides composed of?

ribose, phosphate, and a nitrogenous base.

prokaryotes condense dna by…

supercoiling & various proteins

eukaryotes condense dna through…

histone interactions

what is the correct model of the Messelson and Stahl Experiment

semi-conservative

what is the OriC

the sequence where dna replication starts in bacteria (origins on replication)

what do initator proteins do?

attach to a origin of replication and causes a section of dna to unwind

what is a helicase

a enzyme

what is the helicase enzyme function for replication ?

to unwind dna by breaking the hydrogen bonds between the bases

what do single stranded binding proteins do during replication?

tightly attach to the exposed single stranded dna and prevents secondary structures from forming and interfering with replication

what happens when complimentary base form within a single strand of dna?

a hair pin, stem or a complex looking secondary structure

what is Dna Gyrase

a enzyme

what does the dna gyrase enzyme do during replication?

relieves the strain that builds up ahead of the replication forkhw

what is the replication fork?

the point where the dna molecule splits

what happens to the 2 dna molecule strands after they split

they become separate strands that are now templates for replication

what is a replication bubble?

the entire region of the dna that is unwound and going through replication

dna polymerase III can only create new dna from

an existing 3’ hydroxyl (OH)

what is the main replicative polymerase in E.coli?

dna polymerase 3

what is the enzyme complex made up of?

several polypeptides

what are the 2 main activities during the elongation of new dna

add nucleotides in the 5-3 direction & remove misincorporated nucleotides in the 3-5 direction

what does primrase do

it synthesizes a short reach of RNA complementary to dna template

and provides a 3’ OH so the dna nucleotide can attach

as the replication fork move away from the bubble, the replication bubble ___ in size

increases

while one strand is elongated in a _____ manner, the other is elongated in a ______ manner

continuous, discontinuous

what are Okazaki fragments?

small fragments formed by the discontinuous lagging strand , need to be joined together before replicated ends

what are the characteristics of dna polymerase 1?

it follows dna polymerase 3, and has 5-3 and 3-5 outside enzyme activity

dna polymerase removes _____ and replaces it with DNA ______ using 3’ OH from the neighboring Okazaki fragment

RNA primer , 5-3 polymerase activity.

dna ligase seals the ____

nick slide 23

dna polymerase I cannot join ____ dna stands

adjacent

what is the nick (slide 23)

a break in the sugar-phosphate backbone between 2 strands of dna

dna ligase catalyzed the formation of a phosphodiester bond between adjacent ___

3’ Oh and 5’ phosphate groups (close up slide 23)

what is nucleotide selection?

pairing nucleotides with their complements on the strand

explain the proofreading process

dna polymerase recognize, remove, and replace incorrectly paired nucleotides during replication slide 25

replication is always which model?

semi conservative

dna synthesis begins with the synthesis of short segments of rna called

primers

replication is ___ on the leading strand (right) and ___ on the lagging (left) strand

continuous, discontinuous

which checkpoint makes sure that replication only occurs once at each origin?

g1/s checkpoint

what is the replication end problem?

eukaryotic dna is linear and prokaryotic dna is circular

what is telomerase

how does telomerase temporarily resolve the end replication problem?