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DNA Structure and Function. Chapter 13. Miescher Discovered DNA. 1868 Johann Miescher investigated the chemical composition of the nucleus Isolated an organic acid that was high in phosphorus He called it nuclein We call it DNA (deoxyribonucleic acid). Mystery of the Hereditary Material.

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Miescher discovered dna
Miescher Discovered DNA

  • 1868

  • Johann Miescher investigated the chemical composition of the nucleus

  • Isolated an organic acid that was high in phosphorus

  • He called it nuclein

  • We call it DNA (deoxyribonucleic acid)


Mystery of the hereditary material
Mystery of the Hereditary Material

  • Originally believed to be an unknown class of proteins

  • Thinking was

    • Heritable traits are diverse

    • Molecules encoding traits must be diverse

    • Proteins are made of 20 amino acids and are structurally diverse


Structure of the hereditary material
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

Figure 13.2Page 217


Griffith discovers transformation
Griffith Discovers Transformation

  • 1928

  • Attempting to develop a vaccine

  • Isolated two strains of Streptococcus pneumoniae

    • Rough strain was harmless

    • Smooth strain was pathogenic


Griffith discovers transformation1
Griffith Discovers Transformation

1. Mice injected with live cells of harmless strain R.

2. Mice injected with live cells of killer strain S.

3. Mice injected with heat-killed S cells.

4. Mice injected with live R cells plus heat-killed S cells.

Mice live. No live R cells in their blood.

Mice die. Live S cells in their blood.

Mice live. No live S cells in their blood.

Mice die. Live S cells in their blood.

Figure 13.3Page 218


Transformation
Transformation

  • What happened in the fourth experiment?

  • The harmless R cells had been transformed by material from the dead S cells

  • Descendents of the transformed cells were also pathogenic


Oswald avery
Oswald & Avery

  • What is the transforming material?

  • Cell extracts treated with protein-digesting enzymes could still transform bacteria

  • Cell extracts treated with DNA-digesting enzymes lost their transforming ability

  • Concluded that DNA, not protein, transforms bacteria


Bacteriophages
Bacteriophages

  • Viruses that infect bacteria

  • Consist of protein and DNA

  • Inject their hereditary material into bacteria

bacterial cell wall

plasma membrane

cytoplasm

Figure 13.4bPage 219


Hershey chase s experiments
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?


Hershey and chase results

virus particle labeled with 35S

virus particle labeled with 32P

Hershey and Chase Results

bacterial cell (cutaway view)

label outside cell

label inside cell

Figure 13.5Page 219


Information
Information

  • Mon., 28 November

    • Chapter 14 and 16 highlights

  • Wed., 30 November

    • Final exam review – BRING YOUR QUESTIONS!

    • Instructor evaluations

  • Mon., 12 December, 2:15-4:15pm in C317

    • Final Exam

  • [email protected]

  • Exam 3 will be returned at the end of this class.


Structure of nucleotides in dna
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


Nucleotide bases
Nucleotide Bases

ADENINE

(A)

GUANINE

(G)

phosphate

group

deoxyribose

THYMINE

(T)

CYTOSINE

(C)

Figure 13.6Page 220


Composition of dna
Composition of DNA

  • Chargaff showed:

    • Amount of A relative to G differs among species

    • Always: A=T and G=C


Rosalind franklin s work
Rosalind Franklin’s Work

  • Expert in X-ray crystallography

  • Examined DNA fibers

  • Concluded that DNA was some sort of helix


Watson crick model of dna
Watson-Crick Modelof DNA

  • 2 nucleotide strands

    • Run in opposite directions

    • Held together by H bonds between bases

  • A binds with T and C with G

  • Molecule is a double helix


Dna structure helps explain how it duplicates
DNA Structure Helps Explain How It Duplicates

  • DNA is 2 nucleotide strands held together by H bonds

  • H bonds between 2 strands are easily broken

  • Each single strand then serves as template for new strand


Dna replication
DNA Replication

  • Each parent strand remains intact

  • Every DNA molecule is half “old” and half “new”

new

old

old

new

Figure 13.9Page 222


Base pairing during replication
Base Pairing during Replication

Each old strand serves as the template for complementary new strand

Figure 13.10Page 223


Enzymes in replication
Enzymes in Replication

  • Enzymes unwind the two strands

  • DNA polymerase attaches complementary nucleotides

  • DNA ligase fills in gaps

  • Enzymes wind two strands together


A closer look at strand assembly
A Closer Look at Strand Assembly

Energy for strand assembly is provided by removal of two phosphate groups from free nucleotides

newly

forming

DNA

strand

one parent

DNA strand

Figure 13.10Page 223


Continuous and discontinuous assembly
Continuous and Discontinuous Assembly

Strands can only be assembled in the 5’ to 3’ direction

Figure 13.10Page 223


Dna repair
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


Information1
Information

  • Mon., 28 November

    • Chapter 14 and 16 highlights

  • Wed., 30 November

    • Final exam review – BRING YOUR QUESTIONS!

    • Instructor evaluation

  • Mon., 12 December, 2:15-4:15pm in C317

    • Final Exam

  • [email protected]

  • Exam 3 will be returned ... Now!


E xams
Exams


Grades
Grades

  • A = 100-79

  • B = 78-70

  • C = 69-61

  • D = 60-53

  • Average = 63

  • High = 99


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