Download Chapter 12 Molecular Genetics Identifying the Substance of Genes I

Chapter 12 Molecular Genetics
Identifying the Substance of Genes
I. Bacterial Transformation.
A. Griffith’s Experiments
1.1928, a British scientist named Griffith was trying to find a better way to fight
pneumonia
2. He was studying effects of 2 strains of an infectious bacteria
a. "smooth" strain was found to cause pneumonia & death in mice.
b. "rough" strain did not.
c. He conducted the following experiment:
**He concluded that some molecules or groups of molecules had changed
the harmless rough bacteria into the deadly smooth bacteria. He called
this TRANSFORMATION.
1. Transformation: One type of bacteria (the harmless form) had been
changed permanently into another (the disease causing form).
a. The transforming factor had to be a GENE
B. Avery and DNA
1. 1944 Canadian biologist realized that the Griffith experiment might be the
key to finding out if DNA OR protein carried genetic information.
2. If he and his colleagues were to find out which molecule was needed for the
transformation – they might also be able to find out what makes up genes.
3. Through a series of experiments, the team treated the heat-killed bacteria
with enzymes.
4. The enzymes destroyed the lipids, carbs and other molecules. Destroying
these molecules didn’t affect the change and transformation – it still
occurred.
5. Destroying the DNA blocked transformation.
II. Bacterial Viruses
A. THE HERSHEY-CHASE EXPERIMENT
1. 1952, American scientists, Alfred Hershey and Martha Chase
2. Hershey and Chase designed an experiment where they could label protein
or DNA and then track which entered the E. coli cell during infection.
3. A type of virus that infects bacteria is called a bacteriophage (phage)
4. They knew the phage contained both protein and DNA – if they could see
which of those enter a bacteria during an infection = they would know what
makes up genes.
Protein coat
Squiggles = DNA
5. Conclusion: Viral proteins remain outside cell, Viral DNA injected into
cell, Injected DNA causes cells to produce additional viruses with more
viral DNA and protein => DNA not protein carry genetic information
III. Role of DNA
A. Storing information (remains in the nucleus)
B. Copying information (it’s really transcribed….mRNA is not identical).
C. Transmitting Information
The Structure of DNA
I. The components of DNA
A. Nucleic acids: Are organic compounds—
1. DNA and RNA are complex organic molecules (polymers) that are
made up of nucleotides.
2. Nucleotides are the building blocks of nucleic acids.
a. Made up of…
1. 5 carbon sugar called deoxyribose
2. Phosphate group
3. Nitrogenous base
a. Contain nitrogen
b. DNA has 4 kinds of nitrogenous bases
1. Adenine (A)
2. Thymine (T)
3. Cytosine (C)
4. Guanine (G)
b. Complimentary Base Pairing
1. Adenine pairs with Thymine with two hydrogen
bonds
2. Cytosine pairs with Guanine with three hydrogen
bonds
b. Chargraff – scientist that determined that base pairs
are consistent with in species.
1. Humans: 30% each A and T
20% each C and G
The arrangement of nitrogen bases along one strand (of the double stranded
DNA) is the exact compliment of the other side.
Make the complimentary strand to this DNA strand
A
T
C
G
G
A
A
T
C
T
A
G
T
A
G
C
C
T
T
A
G
A
T
C
A
A
Make the complimentary strand to this DNA strand
C
G
T
T
A
C
G
A
T
G
II. The Double Helix Model
A. The DNA molecule consists of two long strands, which are a chain of
nucleotide monomers.
B. Two strands of DNA are held together by hydrogen bonds
C. Rosalind Franklin in the 1950s used X-ray diffraction to get information about
the structure of DNA. The X-shaped pattern in the photograph showed that the
strands are twisted around each other. Without her contribution Watson and
Crick would not have developed the 3-D double helix model.
D. James Watson and Francis Crick – 1953)
1. 3-D Double Helix model. looks like a twisted ladder
a. The two strands of DNA run in opposite directions. These strands
are antiparallel.
DNA Replication
I. Copying the Code—
A. Replication—Before a cell divides, it must duplicate its DNA in a copying
process called replication.
1. Prokaryotic – singular chromosome, circular
2. Eukaryotic – 1000x more DNA as prokaryotes, DNA in the nucleus, multiple
chromosomes. Each species has a characteristic chromosome number.
Contain both DNA and protein. Chromatin is tightly coiled around proteins
(histones) – they form a bead-like structure called a nucleosome.
a. Nucleosomes can fold LARGE amounts of DNA into tiny spaces &
play a role in how DNA is “read” to make proteins.
B. DNA REPLICATION PROCESS
1. Each strand of DNA has all of the information.
2. DNA helicase attaches to a DNA molecule and moves along unwinding it
by breaking the hydrogen bonds.
3. After the two strands are separated, the unpaired bases pair up with
nucleotides which are freely floating in the nucleus.
4. DNA polymerase, catalyzes the formation of the sugar-phosphate bonds
(connects one nucleotide to the next) and proofreads.(only one error per
1 billion nucleotides.)
5. This results in two new DNA molecules – each having one old and one
new strand
6. Since A can only match up with T and C can only match up with G – the
sequence of nucleotides in each new strand exactly matches that in the
original molecule
7. Replication of DNA doesn’t start at the beginning and end at the end of a
DNA strand – it happens simultaneously all over the DNA Strand. if it
didn’t it would take about 16 days to copy one DNA strand.
8. Semi Conservative Process
A. The original DNA is shown all in blue. The red strands in the
daughter DNA are the ones which have been built on the original
blue strands during the replication process.
B, You can see that each of the daughter molecules is made of half of
the original DNA plus a new strand. That's all "semi-conservative
replication" means. Half of the original DNA is conserved (kept) in
each of the daughter molecules.
C. The red and blue, of course, have no physical significance apart
from as a way of making the diagrams clearer.
**Be able to draw/recognize parts of nucleotide.