DO NOW
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Transcript of DO NOW
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DO NOW
What is DNA?
What does DNA look like?
How do we use DNA in everyday life?
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Objectives
Explain what DNA is and understand it’s significance
Summarize the experiments of Griffith and Avery leading to discovery of DNA as genetic material
Label a diagram of a virus.
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Molecular Genetics
Chapter 12
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DNA
DNA stands for:– Deoxyribonucleic acid
DNA is located:– In the nucleus of cells
The function of DNA is to:– Tells the cells how to produce things that make
you up (Blueprint)
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When was DNA discovered?
We are going to study the scientists who discovered DNA.
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1928 Fred Griffith -
Studied two strains of bacteria, Streptococcus pneumoniae
Worked with two strains of bacteria: Rough Strain and Smooth Strain
S strain causes pneumonia and the R strain does not
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1928 Fred Griffith-
Discovered that something from the heat killed wild type (smooth) bacteria was turning the mutant (rough) type bacteria into smooth.
Called it the transforming factor Didn’t really know what it was
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1944- Avery, McCarty and MacLeod
Purified both protein, RNA, and DNA separately from Streptococcus pneumonia bacteria to determine which would transform the harmless bacteria- How?
Injected protein into bacteria no effect Injected RNA into bacteria no effect Injected DNA into bacteria mice died
Conclusion: DNA is the genetic material!!
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Nobody believed Avery
People thought that Avery had inaccurate results and contamination and still thought the transforming factor could be.
Back to square 1! We know there is a “transforming factor” Is it protein or DNA? Lets ask Hershey and Chase!
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Hershey and Chase
Worked with viruses to determine what the “transforming factor” was.
*Before we discuss their experiment we must understand what a virus is and how it works!*
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Viruses- 6 Characteristics of Viruses
1. Have their own genome (genetic make up) made of either DNA or RNA
2. Does not have enzymes, ribosomes, or ATP
3. Have external protein shells (capsids)
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Viruses- 6 Characteristics of Viruses
4. Infect only specific cells 5. 2 life cycles (lytic and lysogenic)
– Lytic – breaks out and spreads– Lysogenic- hangs around
6. Smaller than bacteria
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Bacteriophage= virus attacking bacteria…
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2 Life Cycles
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5 Stages of Attack!!
1) Attachment: virus attaches to it’s host
2) Injection: virus injects it’s DNA into the host cell.
3) Replication: virus copies it’s genetic material many times.
4) Assembly: virus assembles more viruses
5) Release: Viruses are release from the cell ready to attach to new cells!
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Identify the Stages
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Homework!
Read pgs. 326-328, Summarize the experiments of Griffith and Avery
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2/23 DO NOW
Take out your homework!!! Which strain of bacteria killed the mice in
Griffith’s experiment? What is the process that caused rough
bacteria to become smooth? What did Avery discover? What are the 5 stages of attack for a virus?
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Objectives
Summarize the experiments of Hershey and Chase.
Identify the stages of replication of a virus. Understand the use of viruses in discovering
DNA.
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Lets Review…
Who are the scientists we’ve talked about so far?
What are the 6 characteristics of a virus?
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Viruses!
5 Stages of Attack animation
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1952 Hershey and Chase
Radioactive Labeling:– Used radioactive phosphorus (32P) to identify DNA in the
bacteriophages – Used radioactive sulfer (35S) to identify proteins in the
bacteriophagesTracking DNA
Radioactive bacteriophages infected bacteria cells After review results found radioactive sulfur outside
of bacteria cells and radioactive phosphorus inside bacteria cells
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1952 Hershey and Chase
Used Bacteriophages Two radioactively labeled viruses.
– 1. Sulfur Protein coat– 2. Phosphorous DNA
After infecting cells, only the DNA was still radioactively labeled
DNA is genetic material
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Hershey and Chase…
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Ok… so we KNOW DNA carries Genetic Material, now what?
Levene discovered that DNA is made of nucleotides
What are nucleotides?
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DNA STRUCTURE
Nucleotides:– 5 carbon sugar (Deoxyribose)– Phosphate Group – Nitrogen base
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Nitrogenous Bases
Purines– Double ring structure– *Adenine and Guanine
Pyrimidines– Single ring structure– * Thymine, Cytosine, Uracil
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Nitrogenous Bases
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DNA Structure
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Erwin Chargaff
Chargaff’s rule– C= G – T = A
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Draw in the complimentary sequence
ATGCTAATTCGCATCG
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Rosiland Franklin
X-ray Diffraction use of photo 51
X-ray diffraction data helped solve the structure of DNA
Indicated that DNA was a double helix
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X-Ray Crystallography
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Watson and Crick
Built a model of the double helix that conformed to the others’ research– two outside strands consist of alternating sugar
and phosphate molecules– cytosine and guanine bases pair to each other by
three hydrogen bonds – thymine and adenine bases pair to each other
by two hydrogen bonds
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DNA Structure
DNA often is compared to a twisted ladder.
Rails of the ladder are represented by the alternating deoxyribose and phosphate.
The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.
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Label the parts of the DNA molecule
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Base Pairs- Rungs of the ladder
-2 Strands of DNA form a helix
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Orientation of DNA- Anti Parallel
On the top rail, the strand is said to be oriented 5′ to 3′.
The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.
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Chromosome Structure
DNA coils around histones (proteins) to form nucleosomes,
This coils to form chromatin fibers. The chromatin fibers supercoil to form
chromosomes that are visible in the metaphase stage of mitosis.