Take out your
homework
DNA
• WHY does G pair with C?
• What forces hold the base pairs together?
• What are the three functions of DNA?
• What does ‘antiparallel’ mean?
Sugar - deoxyribose
3’ to 5’
3’ to 5’
5’
3’
5’
3’
5’
3’
5’
The two
strands are
‘antiparallel’
That’s how
the charges
line up
Thymine
Guanine
Cytosine
Adenine
Cytosine
Guanine
DNA
• What are the three functions DNA must
perform?
• Store, Copy, Transmit
• So, how is DNA copied?
DNA
• A little background:
• -ase means enzyme
• enzymes are proteins that control
reactions
• What’s a “polymer”?
• So WHAT does DNA Polymerase do?
DNA
• So, how is DNA copied?
DNA Replication
• What’s the first
thing you have to
do?
• Break the H-bonds
• Helicase does that.
AATGGCTAGC
DNA Replication
• It’s almost that simple
• DNA ‘unzips’ to form a REPLICATION FORK
• DNA Polymerase puts the bases in (but they
have to fit)
• DNA Polymerase only works 5’ to 3’
https://www.youtube.com/watch?v=TNKWgcFPHqw
http://www.hhmi.org/biointeractive/dna-replication-advanced-detail
https://www.youtube.com/watch?v=JZXT2uOcD2w
Review
• What are the roles of:
• DNA Polymerase
• Helicase
• Ligase
• Single-Stranded Binding Protein
• What is the ‘significance’ of the 5 – 3 nature
of DNA and DNA Polymerase?
• Covalent Bond
• Hydrogen ‘bond’ (interaction)
Review
• In eukaryotes, DNA Polymerase can copy
from a few to thousands of bases a SECOND
• DNA Polymerase has ‘proofreading’ ability
• How would it ‘know’?
• Other enzymes can remove just the base later,
if needed.
Homework
• “Solve the Chapter Mystery” p. 357 1- 4