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
How?
 How do genes and chromosomes control the activity of
a cell?
 By producing proteins that regulate cellular functions
or become part of the cell.
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 nondisease 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
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
2.
What is the shape of DNA?
A double helix, or “twisted ladder”
7. Who discovered the shape of DNA?
Watson and Crick
6.
True or False ?
DNA is a very long molecule of many nucleotides
hooked together in a chain.
True
8.
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.
DNA Replication Video
 http://www.youtube.com/watch?v=zdDkiRw1PdU