1. DNA Review

2. The Size of DNA...
If the DNA of one cell is stretched out, it makes a 7 ft. long string
There are about 5 trillion cells in the human body
If you connected all the DNA together, it would be long enough that
it would take light over 10 hours to travel its length
(ruptured bacteria)
This is a whole lot of information

3. DNA Structure
DNA is a Double Helix - like a twisted rubber ladder made from three main components
Sides of the ladder are composed of alternating sugar and phosphate pieces
Each “rung” of the ladder is made up of two complementary bases
A bound to T
C bound to G
DNA is put together in chunks called NUCLEOTIDES
Each nucleotide has a sugar, PO43- and base

4. Nucleotides A nucleotide is held together with strong molecular bonds5’
A nucleotide is held together with strong molecular bonds
Oxygens provide the “hooks” necessary to bind to other NTP’s
We identify where these Oxygens are by labeling the carbons of the deoxyribose sugar 1’ 4’ 3’ 2’
(see, no oxygen at 2’…)

5. DNA Strand
Each of the components of the nucleotide binds to another nucleotide to form a single DNA strand
Since Oxygen easily forms two strong bonds, the phosphate and sugars both bind most strongly
The Hydrogens on the base bind less strongly with an Oxygen or Nitrogen from another base to bind one strand to another

7. ds DNA Helix
Finally we have the characteristics of double stranded DNA
STRONG bonds between the deoxyribose sugars and phosphates
WEAK bonds between the Hydrogen and Oxygen or Nitrogen (weaker between A and T than C and G)
Twisting of the two anti-parallel strands to form a double helix
Heat it up, which bonds break first?...

8. The Replicator DNA is a replicator because of the base pairing reality
Since only one of the bases can pair with only one other of the other bases, each strand is a negative of the other
The process of pulling the strands apart from each other and replacing each single strand with its complement is called REPLICATION
We start with some ds DNA

9. Replication #1 DNA polymerase comes on the scene
UNWINDS the DNA upstream
UNZIPS the DNA
This site is known as the replication bubble

10. Replication #2
Complementary Bases begin adding into both sides of the ds DNA
A binds with T, C binds with G (no other possibility because of the shape of the bases!)
The DNA Polymerase precedes the paired bases and clips out any that are already added ahead of it (on the 3’ end) with an exonuclease activity

11. Replication #3 Finally you have 2 identical copies of ds DNA
The final job of the Polymerase is to Proofread the NTP’s after they are added (back on the 5’ end) and to clip out any that are incorrectly paired

12. Review: DNA Polymerase
Unwinds DNA at the replication fork
Unzips DNA (breaks apart Hydrogen Bonds)
Cuts out nucleotides attaching upstream on the 3’ end
Proofreads back on the 5’ end and cuts out improperly paired bases

13. DNA Structure
and
Replication