Regents Biology
Regents Biology
Regents Biology
Regents Biology
Regents Biology
Paired bases DNA structure
double helix 2 sides like a ladder
Bases match together A pairs with T
A : T C pairs with G
C : G
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Watson and Crick
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DNA Replication Replication is semi-conservative (one strand
is old, one strand new) Each strand serves as a template (or
pattern) for the new strand
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Copying DNA Matching bases allows
DNA to be easily copied
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Making new DNA Copying DNA
replicationDNA starts as a double-stranded
molecule matching bases (A:T, C:G)
then it unzips…
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Origins of Replication
Where DNA Replication starts
Differs between organisms Prokaryotes = 1 origin
of replication Eukaryotes = many
different origins of replication
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DNA replication Strands “unzip” at the weak bonds
between bases
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General Process of DNA Replication Step 1: Initiator Proteins
Bind to origins of replication to begin replication
Attracts other enzymes involved in replication process
Step 2: DNA Helicase separates the DNA
helix
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DNA replication
DNA polymerase
Enzyme DNA polymerase adds new bases
DNA basesin nucleus
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Step 3: Primase Builds a primer at the 5’ end of the new DNA strand
Step 4 :DNA Polymerase III builds the new strand of DNA in the 5’ to
3’ direction
3’ 5’5’
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- Nitrogenous bases are located in the cytoplasm
- They enter the nucleus through the pores in the nuclear membrane
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DNAPolymerase
Copying DNA Build daughter DNA
strand use original parent
strand as “template” add new matching
bases synthesis enzyme =
DNA polymerase
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Problem… How can both strands of DNA be
replicated in a 5’- 3’ direction at the same time if they are antiparallel?
Answer: leading and lagging strands
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Leading and Lagging Strands
Leading strand is synthesized continuously in the direction of replication (goes in the same direction as helicase)
Lagging strand is synthesized in short fragments the opposite direction of replication (opposite direction as helicase)
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DNA Ligase
DNA Ligase Forms covalent bonds between
nucleotides to create a continuous strand of DNA
When DNA Polymerase I edits the DNA strand, DNA Ligase attaches the bases on one side of the DNA strand together.
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DNA Ligase
DNA Ligase seals Okazaki fragments together Forms covalent bonds between
nucleotides to create a continuous strand of DNA
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Thymine is added accidentally.
DNA polymerase cuts the damaged DNA.
The proper base is added.
Ligase joins the two spots.
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New copies of DNA Get 2 exact copies of DNA to split
between new cells
DNA polymerase
DNA polymerase
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Copied Chromosomes
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DNA Replication Replicate the following DNA strand:
A – G – G – C – T – T – C – A – G – T T – C – C – G – A – A – G – T – C - A
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