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Lecture 10

BIOL 1F90 Lecture Notes - Lecture 10: Primase, Senescence, Hydrogen Bond


Department
Biological Sciences
Course Code
BIOL 1F90
Professor
Douglas Bruce
Lecture
10

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Lagging Strand Synthesis
-multiple RNA primers are made (not made at origin; made near replication fork as
single stranded DNA; direction is opposite to fork movement)
-synthesis of DNA is in pieces, Okazaki fragments
fragments are eventually connected to each other to form a continuous
lagging strand
-as synthesis of both strands nears
completion
RNA primers will be removed by a
special DNA polymerase and $lled in
with DNA
 DNA ligase will join adjacent DNA
fragments
Many Proteins are used in DNA
Synthesis
-DNA helicase
binds to DNA and travels 5’ to 3’
using ATP to
separate strand and move fork
forward
-DNA topoisomerase
relieves additional coiling ahead of
replication
fork
-single stranded binding proteins
keep parental strands open to act as
templates
DNA Polymerase
-covalently links nucleotides
deoxynucleoside triphosphate are used by the enzyme
-DNA polymerase breaks a covalent bond to release pyrophosphate (2 phosphate
groups)
provides energy for polymerization
-the remaining deoxynucleoside monophosphate is covalently linked to the growing

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strand of DNA
-2 important features of DNA polymerase
1) DNA polymerase cannot begin DNA synthesis on a bare template strand
alone
-the enzyme can only add nucleotides to a nucleic acid polymer
-DNA primase must make a short RNA primer to act as a starting place
-the RNA primer will be removed and replaced with DNA later
2) DNA polymerase can only work 5’ to 3’
Primase
-makes an RNA primer at the origin
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