DNA
and more
Review
• What organelle is the “control
center” of the cell?
• The nucleus
• What structures are found in
the nucleus?
• Chromosomes
• What structures are located
on chromosomes?
• Genes
• What are chromosomes made
of?
• DNA and protein
Discovery of DNA
• Involved the work of multiple scientists
putting pieces of the puzzle together.
Frederick Griffith – British
Scientist
• In 1928 he wanted to find out how bacteria
produced pneumonia, a serious lung
disease.
• He isolated two types of pneumonia bacteria
from mice.
• One type caused illness when injected into
mice, one didn’t.
• Griffith heated the disease causing strain to
kill the bacteria, and injected it into mice; it
did no harm.
• He then injected
both the heat
killed disease
causing, and the
non-disease
causing strain
into mice, and
they got sick and
died.
Conclusion
• Griffith hypothesized that some factor
was transforming the harmless bacteria
into the bad, harmful strain.
Oswald Avery – Canadian
biologist
• In 1944, he treated an extract made from
the heat-killed bacteria with enzymes, to
kill proteins, lipids, RNA and other
molecules.
• Transformation still occurred.
• He then used different enzymes to break
down DNA, and this time transformation
did not occur.
Conclusions
• Scientists concluded that DNA was the
transforming factor, and that DNA is
the material that stores, and transmits
the genetic information from one
generation to the next.
Hershey and Chase – American Scientists
• In 1952 they studied a bacteriophage
which is a virus (non-living particles
smaller than a cell) that infects bacteria.
• Bacteriophage means “bacteria eater”.
• They experimented and concluded that the
genetic material of a bacteriophage is
also DNA.
Components of DNA
DNA is a long
molecule made of
units called
nucleotides.
Each nucleotide
consists of:
1) A 5-carbon sugar
called deoxyribose
2) A phosphate
group
3) A nitrogenous
base
Four kinds of Nitrogenous
Bases
1.
2.
3.
4.
Adenine – a purine
Guanine – also a purine
Cytosine – a pyrimidine
Thymine – also a pyrimidine
Structure of DNA
• The “backbone consists of the sugar and
phosphate.
• The bases stick out to the side.
• In 1953 Watson and Crick discovered that
DNA was actually in the shape of a double
helix, or “twisted ladder”.
• They found that hydrogen bonds could form
between bases, and that base pairing occurred.
Base Pairing
• Means that in DNA:
• Adenine always pairs with Thymine
• Guanine always pairs with Cytosine
Review
1. What Three Components Make up a
Nucleotide?
▪Deoxyribose (a sugar)
▪A Phosphate Group
▪Nitrogenous Base
2. What is a bacteriophage?
A virus that eats bacteria.
3. What are the four nitrogenous bases?
Adenine, Cytosine, Guanine, Thymine
4. What base does adenine pair with?
Thymine
5. What base does cytosine pair with?
Guanine
6. What is the shape of DNA?
A double helix, or “twisted ladder”
7. Who discovered the shape of DNA?
Watson and Crick
True or False ?
8. DNA is a very long molecule of many
nucleotides hooked together in a chain.
True
DNA Replication
• Before a cell divides it must duplicate
it’s DNA, so that each new daughter
cell will have a complete set of DNA.
This process is called replication.
• During replication, the DNA molecule
separates into 2 strands, then produces
two new complementary strands
following the rules of base pairing.
How does it separate?
• Remember, the bonds that hold the
bases together are weak hydrogen
bonds.
• DNA polymerase is the main
enzyme involved in replication.