Exam Prep 2 Flashcards
(18 cards)
DNA replication
-semi conservative model
Demonstrated by Medellin and stahl with ecoli
Used density gradient centrifugion
DNA synthesis requirements
- Template of single stranded DNA (ssDNA)
- All 4 deoxyribonucleic acids, 5’ triphosphates
- DNA polymerase and other enzymes and proteins
- free 3’ OH group
Catalysis
5’ connects to free OH
To remember about DNA polymerase
- Used deoxyribonucloside 5’ triphosephate
- catalyzes phosphodiester bonds
Synthesis at replication fork
Takes place within the replication bubble
DNA strands are synthesized simultaneously
Theta replication
Replicon
Starting code for replication
Leading strand
Continuous adding of nucleotides
Lagging strand
Short bursts of nucleotides
-Okazaki fragments
About leading and lagging strands
Always 5’ to 3’ end, both antiparallel
Over all synthesis in the direction of replication fork
Lagging strands start by going away but eventual direction is towards the replication fork
Modes of replication
Circular genomes
Linear genomes
Circular genomes
- theta replication - leading and lagging on both sides
2. Rolling circle- viral DNA, nick in the circle free’s OH group
Linear genomes
Humans or eukaryotes
Multiple bubbles of replication
Would take 7 days if there were not multiple
Molecular model of DNA : bacteria
In E. coli protein breaks DNA
- DNA grease reduces torsional strain
- polymerase III begins new strand
- polymerase I (completes, Okazaki fragments)
4 stages of replication
- Initiation
- Unwinding
- replacing RNA nucleotides
- Termination
- Initiation
Initiator proteins
Proteins bind to ssDNA
Helicase binds to lagging strands template and breaks hydrogen bond
- Unwinding
DNA helicases DNA gyrase (topoimerase)
- Termination
When forks meet, end of replication
E Coli. DNApolymerase
Five in E coli
5’ to 3’ activity
Some have exonuclease activity
Pol III primary replication enzymes
