1. Define the following terms and
utilize these terms in an appropriate context:
bidirectional replication
conservative replication
continuous DNA synthesis
dispersive replication
lagging strand
leading strand
nucleosome
Okazaki fragment
ori
origin of replication
primer
replication fork
replicon
semiconservative replication
2. Compare conservative, semiconservative and dispersive modes of DNA replication.
3. Summarize the properties and functions of polymerase I, II and III.
4. Discuss the roles of the polymerase molecules in maintaining the fidelity of the replication process.
5. Define and indicate the significance of A. Okazaki fragments, B. DNA ligase, C. primer RNA during DNA synthesis.
6. Outline the current model for DNA synthesis.
7. Compare and contrast DNA synthesis in prokaryotes and eukaryotes.
8. Show by diagrams how a phosphate group joins the 3' carbon of one deoxyribose to the 5' carbon of the next deoxyribose.
9. Describe the various characteristics of the Watson-Crick double-helix model for DNA.
10. Explain the statement that DNA consists of antiparallel and complementary strands, which read 3'-5' on one strand, but '5-3' on the other.
11. Describe the bonding between the nucleotide bases on one DNA strand and the nucleotide bases of the antiparallel strand.
Resources: Text Chapter 10, Cartoon
Guide pgs. 104-107; 125-128
DNA/RNA Synthesis Replication
Replication Origins
-is there a single
origin or many?
-origin random or in
a specific region?
Replicon- length of DNA replicated following initiation of synthesis at a single origin
Replication fork- point of replication, where strand is unwinding
Bacteria/viruses: single
chromosomes specific region of initiation (ori) entire chromosome one replicon
Eukaryotes: replication
bidirectional
2 replication forks, multiple origins along chromosome (eventually merge)
multiple replicons (because of length allows for quicker replication)
DNA Synthesis: A model
Semiconservative; bidirectional
1. mechanism by which
helix is denatured and stabilized so that replication can occur in both
directions
-helicase
-single strand-DNA binding protein (binds to newly seperated DNA
strands to prevent reassociation)
2. As unwinding proceeds
tension created, must be reduced
-DNA gyrase (DNA topoisomerase), causes break in both strands which is
resealed after tension
lessened
3. Primer created so
polymerization can commence under direction of DNA polymerase (requires
a free 3'
end)
-RNA primase
-DNA polymerase adds 5" nucleotides
4. Synthesis of complementary
strands
Strands are antiparallel
5' ---> 3'
3' <--- 5'
-continuous replication in the direction of replication fork possible only
on one of two strands
-other strand discontinuous in opposite direction
Leading strand- strand of continuous replication
Lagging strand- strand of discontinuous replication; Many points of
initiation
Okazaki fragments- short fragments of DNA 1000-2000 nucleotides
long that are enzymatically
joined to create longer DNA strand
-occur on lagging strand
5. RNA primers must
be removed
DNA ligase- enzyme that can unite smaller fragments of DNA
-joins gaps created by removal of primer
-joins Okazaki fragments.
6. Replication occurs along length of replicon
Fidelity of Synthesis
Complicated processes
need safeguards
-RNA primer
-discontinuous replication
-semiconservative replication
-complementary base pairing
In addition:
-Small alphabet of 4 letters
-very few rules ---> A-T; C-G
DNA polymerases- proofreading activity
-will discontinue synthesis if previous base pair is mismatched
Genes have been identified
for the production of products involved in:
-origin of synthesis
-helix unwinding and stablization
-initiation and priming
-relaxation of supercoiling
-repair and ligation
Recombination at the
molecular level
-crossing over in meiosis can be between two seperate DNA molecules (usually
homologous) or
intramolecular
-genetic recombination
Models depend on:
1. 2 homologous double-stranded DNA molecules
2. Complementarity between DNA strands
3. series of enzymatic processes to accomplish recombination, pg 188