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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
CONCEPT: HISTORY OF DNA RESEARCH
● Griffith’s experiment provided early evidence for DNA as the molecule of heredity.
□ Transformation – a genetic change resulting form the incorporation of foreign DNA into a bacteria
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● The Hersey-Chase experiments helped confirm that DNA is the genetic material.
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: HISTORY OF DNA RESEARCH
● Watson, Crick, and Franklin determined the structure of DNA.
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● The Meselson-Stahl experiment showed DNA is replicated in a semiconservative manner.
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: DNA REPLICATION
DNA replication has three stages: initiation, elongation, and termination.
● Prokaryotic replication begins at a single origin of replication.
● Helicase – separates the two parent strands of DNA
● Topoisomerase – relieves the strain on the DNA strands around the replication bubble
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● Single-strand binding proteins – bind a stabilize single-stranded DNA
● Primase – synthesizes an RNA primer at the 5’ ends
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● DNA polymerase III – synthesizes new strand by polymerizing nucleotides, using parent strand as a template
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: DNA REPLICATION
● DNA polymerase I – removes RNA primer and replaces with DNA nucleotides
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Synthesis of new DNA only occurs in the 5’à3’ direction, the result is:
● Leading strand – the strand synthesized in a continuous manner
● Lagging strand – the strand synthesized in a discontinuous manner
□ Okazaki fragments – the segments of lagging strand
□ DNA Ligase – joins together (ligates) the Okazaki fragments with a phosphodiester bond
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: DNA REPLICATION
● Eukaryotic replication requires multiple origins of replication, and involves different enzymes.
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● The various proteins involved in replication interact to form a DNA replication complex.
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: PROOFREADING AND REPAIR
DNA must be replicated and maintained with a great degree of accuracy.
● DNA polymerase III is capable of proofreading the newly synthesized DNA.
□ If a mismatch occurs during synthesis, the enzyme recognizes and removes it before continuing.
● Mismatch repair – repair mechanism to correct base pairing mismatches after synthesis is complete
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There are many repair mechanisms that function independently of replication, because DNA is constantly damaged.
● Nucleotide excision repair – repair damage from chemicals and radiation that distort the shape of DNA
□ Particularly important for repairing UV light damage, which can result in thymine dimers.
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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CONCEPT: TELOMERES
During eukaryotic replication, the lagging strand ends cannot be replicated by DNA pol III alone.
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● Telomere – a region of repetitive nucleotide sequences that protects the ends of chromatids
□ Telomerase – an enzyme that adds DNA repeat sequences to the 3’ end of the leading strand
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BIOLOGY - CLUTCH
CH.16 - DNA SYNTHESIS
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