How DNA makes a cell
Chapter 12
It always starts with an accident!
• In 1928 ________ was trying to find a vaccine
for __________
• He started by trying to understand why one
strand was so virulent and the other was not
– The ___ strand was __________and has a rough
exterior
– The ___ strand was _________ and had a smooth
exterior.
• He never found a vaccine but stumbled upon
clues of inheritance.
No vaccine, but a new question
• He injected mice with different combinations of the two
bacterium's hoping to find a combo that gave resistance… here is
what he found…
• He concluded ____________________________
_________________________________________
__________________________________________
• They didn’t know how or why!
DNA or Protein
• Since Griffith’s time there
was a debate– DNA or
Protein, which was
responsible for passing on
heritable traits?
• ______ ___ _______ (Chase
is the woman) did the
experiment that proved it
was DNA
• Used viruses
(________________) which
contain only DNA and protein
The Experiment…
• They knew that a virus made other viruses by pirating a bacterial
host (I’ll explain)
• They didn’t know if it was the protein or DNA that had the code
to make new viruses so…
– They made two kinds of viruses
• Radioactive protein
• Radioactive DNA
– Let them infect bacteria
– Separated the liquid they were in from the bacteria
– In the radioactive protein mix they found the radioactivity in the
liquid (_____________________
_________________________________________)
– In the radioactive DNA mix they found the radioactivity in the
bacteria ____________________
______________________________)
• Therefore _____________________________
_________________________________________
Supernatant=
Liquid
Enter Watson and Crick
• We are going to watch a whole movie
about them!
• They came up with the very structure of
DNA– and won the Nobel Prize
• They used (and abused) Rosalind
Franklin… you’ll see!
Structure of DNA
• The nucleotide structure was known long before the molecular
structure
• 4 base pairs (nitrogenous bases)
Nucleotide
–
–
–
–
Adenine
Guanine
Cytosine
Thymine (Uracil in RNA)
• Attached to a sugar (deoxyribose or ribose) and phosphate
backbone
What Watson and Crick discovered
(and Rosalind)
• DNA links up along the ___________ (sugarphosphates)
• Then ____ __________ _____________ and
wrap around in a double helix (alpha helix)
• Don’t forget one is right side up and one is
upside down
So if DNA passes on (and it does) it needs to
have a copying system (and it does!)
• DNA undergoes _____ __________ replication
(each new molecule has one old and one new
strand)
• First it pulls apart into two strands, then pair
in new bases… AT and GC
• Sounds simple right? But what is the
mechanism (oh no!)
More on replication
• To make a new copy we need an enzyme
(speed things up)
• ______ ___________is our guy
• Synthesizes DNA from the ____
________ (Wants itself to start with out
an OH… mirrors the 3’)
• On the 3’ parental end the DNA is just
run off real fast–(______ __________)
• On the 5’ end (_____ _______) it is done
in little 5’3’ pieces (Okazaki fragments)
then put together at the end (like
making individual copies of each page)
– A 2nd enzyme then puts the individual
pages together (DNA ligase)
When finished there is one from the parent and
one new strand in each molecule
Which is leading?
Lagging?