dna replication. facts: dna replicates before a cell divides occurs during the s or synthesis phase...
TRANSCRIPT
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DNA Replication
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Facts:
DNA replicates before a cell divides
Occurs during the S or synthesis phase of mitosis
Replication creates identical copies of DNA strands
Takes place in the nucleus
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3
NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)
““Rungs of ladder”Rungs of ladder”
““Legs of ladder”Legs of ladder”
Phosphate &Phosphate &Sugar BackboneSugar Backbone
DNA Double HelixDNA Double Helix
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Replication:
Begins atBegins at Origin of ReplicationOrigin of Replication Two strands open forming a Two strands open forming a
Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)
New strands grow at the forksNew strands grow at the forks
ReplicationReplicationForkFork
Parental DNA MoleculeParental DNA Molecule
3’
5’
3’
5’
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Enzymes
The Enzyme, The Enzyme, Helicase,Helicase, unwinds and separates the unwinds and separates the 2 DNA strands by breaking 2 DNA strands by breaking the weak hydrogen bondsthe weak hydrogen bonds
DNA polymeraseDNA polymerase adds adds nucleotides complimentary nucleotides complimentary to the parental strandto the parental strand
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Mutations
What do you think a mutation is?
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Proofreading
- Replication occurs at multiple sites along the DNA
- DNA polymerase is very accurate- However mutations do occur- Proofreading occurs continuously
by DNA polymerase
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More practice
Write the complimentary strand:
T A C G G A C T A A C G C
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More practice
Write the complimentary strand:
T A C G G A C T A A C G CA T G C C T G A T T G C G
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Review:
If there is 20% Thymine bases on a DNA strand what are the percentages of the other three bases?
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Answer:
20% Thymine = 20% Adenine20% + 20% = 40 % 100% - 40% = 60% 60% / 2 = 30%30% Cytosine and 30% Guanine
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Review
When and where does DNA replication occur?
What is the relationship between adenine and thymine called?
What are the two enzymes involved in DNA replication?
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Activity
In pairs you are going to create your own DNA models.
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Pieces
Sugar - Black pentagon Phosphate - White tube Nitrogenous bases -
– Adenine - Orange (5)– Guanine - Yellow (4)– Cytosine - Blue (4)– Thymine - Green (5)
Hydrogen bonds - White rods
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Procedure
Create 18 nucleotidesPut together a 9 rung ladder of DNABe sure to have correct base pairingAfter having a complete DNA molecule
create 18 more nucleotides
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DNA replication
Begin to “unzip” DNA molecule from one end
Add complimentary nucleotides to create two DNA molecules