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DNA
DNA
We know traits
are inherited
but how are
they inherited?
Federick Griffith and Transformation
• 1928 bacteria experiment
• Trying to learn how
certain types of bacteria
caused pneumonia.
• Isolated two strains of
pneumonia bacteria from
mice
• He learned something
else..
Experiment
• Mixed heat-killed
slimy bacteria with
rough bacteria
• Injected this into
mice
• All the mice die of
pneumonia!
• Examined dead
mice- all showed
slimy bacteria!
What happened was called
TRANSFORMATION!
• Something in the slimy bacteria turned the
harmless bacteria into a lethal form
• Griffith conclusion:
when deadly bacteria was killed and mixed with living
non-deadly bacteria, a FACTOR transformed the
harmless bacteria into a lethal form.
• 1944: Oswald Avery
• Separated the heat-killed deadly bacteria into its
biochemical parts
• Lipids
• Carbohydrates
• Proteins
• Nucleic acids
Avery’s conclusion:
showed that it was
NUCLEIC ACIDS
(DNA) that caused
Transformation!
Avery & other scientists discovered that
nucleic acid DNA stores & transmits
genetic information from generation to
generation.
Genes are made from DNA?
Prove it!
X-ray Evidence
• 1952 Rosalind Franklin took an x-ray
diffraction to take picture of DNA
shape
• Picture gave clues to structure of DNA
Watson & Crick
• Using everyone else’s
work, Watson & Crick
made a model of DNA
• Created with cut-out
pieces held together
with wire
• Won Nobel Prize
Watson and Crick’s
model of DNA was a
double helix- two
strands were
wound around each
other.
The Hershey-Chase Experiment
• Studied viruses
• 1952- used
bacteriophage virus
» DNA/RNA core
» Protein coat
• Experiment to
determine which part of the virus, the
DNA or the protein, enters a
bacterium and directs it to make more
phages
DNA?
PROTEINS?
• They grew viruses in cultures containing
radioactive elements
• Some with radioactive PROTEINS
• Others with radioactive NUCLEIC ACIDS
• Only nucleic acids displayed in the new virus
• Using viruses and radioactive markers, Hershey and
Chase concluded that the genetic material of the
bacteriophage was DNA, not protein
The Components & Structure of
DNA
Nucleotide
1. 5-carbon sugar
DEOXYRIBOSE
2. Phosphate
group
3. Nitrogenous
base
i. Adenine
ii. Thymine
iii. Guanine
iv. Cytosine
Chargaff’s Rule
• Something
interesting about
nucleotides
• %A=%T
• %C=%G
- SUGAR & PHOSPHATE form backbone/sides
- The BASES form the “steps” of ladder, held
together by Hydrogen bonds
• C-G = 3 hydrogen bonds
• A-T = 2 hydrogen bonds
Chromosomes:
packages of DNA
• Bacteria have single,
circular strand of DNA
• E. coli has 4 million+
base pairs in DNA!
• Many eukaryotes have
1000 times the amount
of DNA as prokaryotes
How is DNA packed in a
eukaryotic cell?
• Coiling: Chromatin is wrapped around
proteins called histones forming beads
• These beads pack together, forming
nucleosomes.
DNA Replication
• Each side of DNA is called a “template mechanism”
• Parent strand: original copy of DNA, used as template
• Daughter strand: newly synthesized complement
How do you replicate something
so long?
1. Replication occurs at hundreds of places
(“ORIGINS”)
2. Moves in BOTH directions until each
chromosome is completely copied
3. Uses ENZYMES to speed up process
What phase in the cell cycle does replication take
place? S Phase!
Why does DNA replication occur? makes sure each
cell will have a complete set of DNA
Where
does this
happen?
Nucleus!
1. DNA unwinds
2. DNA HELICASE enzyme unzips the weak
hydrogen bonds between base pairs
3. Complementary RNA PRIMERS are added
to the DNA to begin copying.
4. DNA POLYMERASE enzyme matches up
DNA nucleotides to 3’-5’ end
continuously(“leading strand”) and later
the RNA primers are replaced with DNA
nucleotides
5. To add nucleotides to 5’-3’ end (“lagging
strand”), RNA PRIMERS are first added
using PRIMASE to attach small DNA
fragments called OKAZAKI FRAGMENTS.
6. DNA Polymerase removes the RNA and
replaces it with DNA bases.
7. These fragments are “glued” together
using DNA LIGASE
DNA REPLICATION
can you spot all the enzymes?
New Strand
Original strand
“Semi-conservative”- why?
PRACTICE!!
• DNA strand is TACGTT
What is the complementary strand?
• ATGCAA
• CAGTAC is the DNA strand
What is the complementary strand?
• GTCATG
• AGCTAGATC is the DNA strand
What is the complementary strand?
• TCGATCTAG