Upload
abigail-ramirez
View
215
Download
1
Tags:
Embed Size (px)
Citation preview
DNA Replication
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
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
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’
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
Mutations
What do you think a mutation is?
Proofreading
- Replication occurs at multiple sites along the DNA
- DNA polymerase is very accurate- However mutations do occur- Proofreading occurs continuously
by DNA polymerase
More practice
Write the complimentary strand:
T A C G G A C T A A C G C
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
Review:
If there is 20% Thymine bases on a DNA strand what are the percentages of the other three bases?
Answer:
20% Thymine = 20% Adenine20% + 20% = 40 % 100% - 40% = 60% 60% / 2 = 30%30% Cytosine and 30% Guanine
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?
Activity
In pairs you are going to create your own DNA models.
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
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
DNA replication
Begin to “unzip” DNA molecule from one end
Add complimentary nucleotides to create two DNA molecules