Agenda 1.Review homework 2.DNA replication 3.Begin HW (DNA Replication worksheet) 4.Quiz will be...
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Transcript of Agenda 1.Review homework 2.DNA replication 3.Begin HW (DNA Replication worksheet) 4.Quiz will be...
Agenda
1. Review homework
2. DNA replication
3. Begin HW (DNA Replication worksheet)
4. Quiz will be Wednesday instead and will include DNA replication
#7
If 15% is Adenine, 15% is also Thymine
That leaves 70% split between Guanine and Cytosine.
So 35% each
#10
Why 99% of it is non-coding
What that 99% does
How the environment affects gene expression
Where it came from/how it originated
DNA Replication
Watson and Crick noticed the huge benefit of double strands
Each strand can serve as a template for making the other
Semiconservative Model Each strand serves
as a template for the creation of a new strand of DNA
2 DNA molecules are created, each containing 1 strand of the original DNA
DNA Replication is Remarkably Fast and Accurate!
Humans have 46 chromosomes, and thus 46 DNA molecules
About 6 billion base pairs
DNA replication takes just a few hours, even in humans
Only 1 error per 1 billion nucleotides
DNA is Antiparallel
• Strands run opposite directions
• DNA polymerase only works in one direction
• So the two strands are built in opposite directions
Leading vs. Lagging Strands
Leading• Built in one piece
• Built in the overall direction of replication
• Only one primer needed
Lagging• Built in pieces
called Okazaki fragments
• Built in the opposite direction of replication
• Many primers needed
Step 5 - Proofreading
Nucleases cut out (incise) the incorrect nucleotide
DNA polymerase adds the correct nucleotide
Ligase connects the new nucleotide to the strand