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’

5’

3’

5’ 3’ to 5’

5’

3’

5’

3’ to 5’

The two strands are ‘antiparallel’

That’s how the charges line up

Adenine

Guanine

Cytosine

Thymine

GuanineCytosine

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