Transcript Ch122008–i only

Chapter 12
DNA & RNA
Interest Grabber
Section 12-1
Order! Order!
Genes are made of DNA, a large, complex molecule. DNA is composed
of individual units called nucleotides. Three of these units form a code. The
order, or sequence, of a code and the type of code determine the meaning
of the message.
1. On a sheet of paper, write the word cats. List the letters or units that
make up the word cats.
2. Try rearranging the units to form other words. Remember that each
new word can have only three units. Write each word on your paper,
and then add a definition for each word.
3. Did any of the codes you formed have the same meaning?
4. How do you think changing the order of the nucleotides in the
DNA codon changes the codon’s message?
I.DNA
 A. Griffith & Transformation
 Frederick Griffith was trying to figure out how bacteria
made people sick-how they cause a certain type of
pneumonia.
 He isolated 2 strains(types) from mice-both cultured
well,but only one caused pneumonia.The culture of the
disease causing bacteria were
__________________colonies while the other was
rough.
smooth

1-Griffith’s experiments (1928)
 Mice injected w/ disease –causing strain got sick
and died and nothing happened if injected w/other
strain…He wondered if the disease-causing type
made a toxin…?
 So he took some of disease strain and heated to kill
bacteria and then injected into mice….mice survived
suggesting it was not a toxin producing disease
Figure 12–2 Griffith’s
Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Figure 12–2 Griffith’s
Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)




2-Transformation
He mixed his heat –killed w/ live harmless bacteria and
injected into mice…..________________________
Somehow the disease –causing strain passed their
disease capacity to harmless bacteria….. disease –
causing strain found in lungs
He called this changing of one bacteria by the genes of
another _____________________....Thus a
factor(gene) from heat killed disease –causing strain
was passed on.
Mice developed
pneumonia
transformation
B. Avery & DNA
 Team of scientists lead by Avery in 1944 repeated
Griffith’s experiment in order to determine which
molecule was responsible for the transformation.
 They made an extract from the heat-killed bacteria
and treated it w/enzymes that kill proteins,lipids and
other molecules,inc. RNA
Avery cont’d
transformation
 ____________________still occurred so the above
molecules were not responsible for transformation
 They repeated the experiment but used enzymes that
kill____________, stopping transformation…. DNA
 Therefore ________caused the transformation and
thus stores and transmits genetic info
C. The Hershey –Chase Experiment
 1952-Alfred Hershey and Martha Chase studied
viruses-disease-causing particles smaller than a cell.
 ______________________-virus that infects
bacteria.They have a DNA or RNA core and a protein
coat…They attach to the surface of a bacterium and
inject genetic info into cell.The viral genes act to
produce many new bacteriophages and eventually
destroy bacterial cell,w/_____________bursting out.
bacteriophage
viruses
 They grew viruses in cultures containing
_________________________________,mixed them
w/bacteria and waited a few min. for viruses to inject
genetic material.
 Then they separated the bacteria from the viruses
and tested bacteria for radioactive marker…..nearly
all the radioactivity was P-32-found in _________---thus concluding it was the genetic material was
DNA !
Radioactive
markers
DNA
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
D. The Components and Structure of
DNA
 Scientists questioned how the DNA molecule could
do three things 1)carry info from 1 generation to the
next 2)putting that info to work and 3)could be easily
copied
 DNA is a long molecule made of units called
___________________________________________-
nucleotides
The nucleotide is made of 3 basic
parts:______________________(sugar),
a phosphate group and
a_________________________________
deoxyribose
Nitrogenous base
 2 nitrogenous bases are purines(have 2
rings):___________________________(A)and_______
(G)
 2 other nitrogenous bases are pyrimidines (have 1
ring):____________________(C)and
____________________________(T)
Adenine ,guanine
Cytosine and
thymine
--backbone made by sugar and phosphate w/ bases sticking
out sideways
Figure 12–5 DNA
Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose

1-_______________________Rules-discovered that
%’s of Cytosine and guanine were almost equal in
DNA and the same was true for adenine and
thymine….Thus A pairs w/T and C w/ G-BASE
PAIRING
Chargaff’s Rules
Percentage of Bases in Four
Organisms
Section 12-1
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8

2- X-ray evidence-1950’s –Rosalind Franklin
used X-ray diffraction to learn about DNA
structure----The scattered X pattern seen begins to
show the __________-partial TWISTED
STRUCTURE of DNA
helix
 3---Double helix_


Watson and Crick -2 strands wound around each
other---like the twisted ladder or spiral staircase
Strands held together by H-bonds
Figure 12–7 Structure of
DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)