Download Chapter 11: DNA

Chapter 11: DNA
In the beginning…
• Is the genetic material in cells protein or DNA?
• In order to be the genetic material, it must be…
1. Able to store information that pertains to the
development, structure and metabolic activities
of the cell
2. Stable so that it can be replicated
3. Able to undergo changes (mutations) to allow
for genetic variation and evolution
The BIG Question…
• How can DNA carry the genetic code?
• Proteins contain 20 different amino acids that can
be organized in countless ways to determine
traits
• Nucleic acids only contain 4 different nucleotides
Scientists that helped us figure it out…
• Frederick Griffith
– Was trying to find a
vaccine against
pneumonia
– Found that one type of
bacteria could turn into
another
(transformation)
• Avery
– Determined that
Griffith’s results were
due to DNA and not
protein
Scientists that helped us figure it out…
• Hershey – Chase
– Worked with viruses that
infect bacteria
(bacteriophages)
– Used radioactive sulfur
to tag protein and
radioactive phosphorus
to tag DNA
– The radioactive DNA
moved into the bacteria
– Proved that DNA is the
genetic material in
viruses
Scientists that helped us figure it out…
• Chargaff
– Compared ratios of the 4 nucleotides
– Found that in every species
A = T and G = C
– This is known as Chargaff’s rule
• Pyrimidine nucleotides – single ringed
– thymine and cytosine
• Purine nucleotides – double ringed
– adenine and guanine
• Always match a pyrimidine with a purine
Scientists that helped us figure it out…
• Franklin and Wilkens
• Used X-ray diffraction to take pictures of DNA
Scientists that helped us figure it out…
• Watson and Crick
• Put it all together and made the model!
• DNA is a double helix
– Sides of the ladder are deoxyribose and phosphate
groups. These are held together by covalent bonds
– The rungs of the ladder are the nitrogenous bases.
These are held together by hydrogen bonds
More DNA deets
• DNA is a polymer of nucleotides:
– One base
– Sugar – deoxyribose
– Phosphate group
• The deoxyribose carbons are numbered:
– 1’  nitrogenous base
– 5’  phosphate group
– 3’  (hydroxide group) next phosphate group
• The chains lie side by side in an antiparallel
orientation
– 5’ end to 3’ end
DNA Replication
DNA Replication…
• The process by which DNA makes a copy of itself
• Occurs during interphase, before cell division
• Semi-conservative: half of the original strand is
always conserved to make the new strand
• Enzymes are involved:
– DNA helicase: separates the strands of the DNA
molecule by breaking the hydrogen bonds between
the nitrogenous bases – this forms a replication fork
– DNA polymerase: moves from the 3’ end toward the
5’ end of the template strand and adds nucleotides
– DNA ligase: binds the Okakazi fragments together
Replication…
• New nucleotides can only be added in the 5’ to 3’
direction.
• The side where this happens easily is called the
leading strand.
• The opposite strand is the lagging strand. Small
sections are worked on. These new sections are
called Okakazi fragments.
• There are multiple replication forks all up and
down the DNA strand.
• http://www.stolaf.edu/people/giannini/flash
animat/molgenetics/dna-rna2.swf
• http://highered.mcgrawhill.com/olc/dl/120076/bio23.swf
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