DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s...
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Transcript of DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s...
![Page 1: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/1.jpg)
DNA Structure and Function
Chapter 12
![Page 2: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/2.jpg)
Structure of the Hereditary Material
• Experiments in the 1950s showed that DNA is the hereditary material
• Scientists raced to determine the structure of DNA
• 1953 - Watson and Crick proposed that DNA is a double helix
![Page 3: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/3.jpg)
Bacteriophages
• Viruses that infect bacteria
• Consist of protein and DNA
• Inject their hereditary material into bacteria
cytoplasm
bacterial cell wall plasma
membrane
![Page 4: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/4.jpg)
Hershey & Chase’s Experiments
• Created labeled bacteriophages– Radioactive sulfur
– Radioactive phosphorus
• Allowed labeled viruses to infect bacteria
• Asked: Where are the radioactive labels after infection?
![Page 5: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/5.jpg)
virus particle labeled with 35S
virus particle labeled with 32P
bacterial cell (cutaway view)
label outside cell
label inside cell
Hershey and
Chase Results
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Structure of Nucleotides in DNA
• Each nucleotide consists of
– Deoxyribose (5-carbon sugar)
– Phosphate group
– A nitrogen-containing base
• Four bases
– Adenine, Guanine, Thymine, Cytosine
![Page 7: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/7.jpg)
Nucleotide Bases
phosphate group
deoxyribose
ADENINE (A)
THYMINE (T)
CYTOSINE (C)
GUANINE (G)
![Page 8: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/8.jpg)
Composition of DNA
• Chargaff showed:
– Amount of adenine relative to guanine
differs among species
– Amount of adenine always equals amount
of thymine and amount of guanine always
equals amount of cytosine
A=T and G=C
![Page 9: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/9.jpg)
Rosalind Franklin’s Work
• Was an expert in x-ray crystallography
• Used this technique to examine DNA fibers
• Concluded that DNA was some sort of helix
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Watson-Crick Model
• DNA consists of two nucleotide strands
• Strands run in opposite directions
• Strands are held together by hydrogen
bonds between bases
• A binds with T and C with G
• Molecule is a double helix
![Page 11: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/11.jpg)
Watson-Crick Model
![Page 12: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/12.jpg)
DNA Structure Helps Explain How it Duplicates
• DNA is two nucleotide strands held
together by hydrogen bonds
• Hydrogen bonds between two strands
are easily broken
• Each single strand then serves as
template for new strand
![Page 13: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/13.jpg)
DNA Replication
newnew old old
• Each parent strand
remains intact
• Every DNA
molecule is half
“old” and half “new”
![Page 14: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/14.jpg)
Base Pairing During
Replication
Each old strand serves as the template for complementary new strand
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Enzymes in Replication
• Enzymes unwind the two strands
• DNA polymerase attaches
complementary nucleotides
• DNA ligase fills in gaps
• Enzymes wind two strands together
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A Closer Look at Strand Assembly
Energy for strand assembly is provided by removal of two phosphate groups from free nucleotides
newlyformingDNAstrand
one parent DNA strand
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Continuous and Discontinuous Assembly
Strands can only be assembled in the 5’ to 3’ direction
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Fig. 12.10, p. 197
newlyformingDNAstrand
oneparentDNAstrand
continuous assembly on one strand
discontinuous assembly on other strand
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DNA Repair
• Mistakes can occur during replication
• DNA polymerase can read correct
sequence from complementary strand
and, together with DNA ligase, can
repair mistakes in incorrect strand
![Page 20: DNA Structure and Function Chapter 12. Structure of the Hereditary Material Experiments in the 1950s showed that DNA is the hereditary material Scientists.](https://reader035.fdocuments.us/reader035/viewer/2022062404/55159d6d55034691418b5ec8/html5/thumbnails/20.jpg)
Cloning
• Making a genetically identical copy of
an individual
• Researchers have been creating clones
for decades
• These clones were created by embryo
splitting
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• Showed that differentiated cells could
be used to create clones
• Sheep udder cell was combined with
enucleated egg cell
• Dolly is genetically identical to the
sheep that donated the udder cell
Dolly: Cloned from an Adult Cell