DNA and RNA Biology In 1928 British scientist
DNA and RNA Biology
• In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia. • He isolated two different strains of pneumonia bacteria from mice and grew them in his lab. Copyright Pearson Prentice Hall http: //upload. wikimedia. org/wikipedia/commons/b/b 8/Fred_Griffith_and_%22 Bobby%2 2_1936. jpg Griffith and Transformation
Griffith and Transformation • (1) The diseasecausing strain of bacteria grew into smooth colonies on culture plates. • (2) The harmless strain grew into colonies with rough edges. http: //www. bio. miami. edu/~cmallery/150/gene/sf 11 x 1 a. jpg
Griffith’s four individual experiments • Experiment 1: Mice were injected with the diseasecausing strain of bacteria. The mice developed pneumonia and died. Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick. Copyright Pearson Prentice Hall
• Experiment 3: Griffith heated the diseasecausing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived. Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died. Copyright Pearson Prentice Hall
Griffith and Transformation • Griffith concluded that the heat-killed bacteria passed their diseasecausing ability to the harmless strain. • Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones Copyright Pearson Prentice Hall
Avery and DNA • Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation. • Avery and his colleagues made an extract from the heat-killed bacteria that they treated with enzymes. http: //www. genoscope. cns. fr/externe/Histoire. BM/avery. jpg Copyright Pearson Prentice Hall
Avery and DNA • Avery repeated the experiment using enzymes that would break down DNA. • When DNA was destroyed, transformation did not occur. Therefore, they concluded that DNA was the transforming factor. • The nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next. Copyright Pearson Prentice Hall
The Hershey-Chase Experiment • Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms. Copyright Pearson Prentice Hall http: //www. ndpteachers. org/perit/Chase%20&%20 Hershey%201953. JPG
The Hershey-Chase Experiment • Bacteriophages – A virus that infects bacteria – Composed of a DNA or RNA core and a protein coat. Copyright Pearson Prentice Hall
The Hershey-Chase Experiment • The virus attaches to the surface of the cell and injects its genetic information into it. • Takes control of cell to make more viruses • When the cell splits open, hundreds of new viruses burst out. http: //www. canlilarbilimi. net/k/baktrfjm/images/bacteriophage_jpg. jpg Copyright Pearson Prentice Hall
The Hershey-Chase Experiment • If Hershey and Chase could determine which part of the virus entered an infected cell, they would learn whether genes were made of protein or DNA. • They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32 P) and sulfur-35 (35 S). Copyright Pearson Prentice Hall
The Hershey-Chase Experiment
The Hershey-Chase Experiment • Nearly all the radioactivity in the bacteria was from phosphorus (32 P). • Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein. Copyright Pearson Prentice Hall
The Structure of DNA • Nucleotides are building blocks that make up DNA Ø 3 main parts: Ø 5 carbon sugar— deoxyribose ØPhosphate group ØNitrogenous base
The Structure of DNA • There are four kinds of bases in in DNA: • • adenine guanine cytosine thymine Copyright Pearson Prentice Hall
The Structure of DNA • The backbone of a DNA chain is formed by sugar and phosphate groups of each nucleotide. • The nucleotides can be joined together in any order. Copyright Pearson Prentice Hall
The Structure of DNA • Chargaff's Rules – Erwin Chargaff discovered that: • The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. • The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. Copyright Pearson Prentice Hall
• X-Ray Evidence – Rosalind Franklin used X-ray diffraction to get information about the structure of DNA. Copyright Pearson Prentice Hall http: //www. chem-is-try. org/wpcontent/uploads/2009/03/rosalind-franklin. jpg The Structure of DNA
The Structure of DNA • Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied. http: //history. nih. gov/exhibits/nirenberg/images/photos/03_wat. Crk_pu. jpg Copyright Pearson Prentice Hall
The Structure of DNA • Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other. http: //gregortimlin. files. wordpress. com/2009/05/watsonjames-crickfrancis. jpg
The Structure of DNA Double Helix Copyright Pearson Prentice Hall
The Structure of DNA • Watson and Crick discovered that hydrogen bonds can form only between certain base pairs— adenine and thymine, and guanine and cytosine. • This principle is called base pairing. Copyright Pearson Prentice Hall
DNA Structure
Avery and other scientists discovered that a) DNA is found in a protein coat. b) DNA stores and transmits genetic information from one generation to the next. c) transformation does not affect bacteria. d) proteins transmit genetic information from one generation to the next. Copyright Pearson Prentice Hall
The Hershey-Chase experiment was based on the fact that a) DNA has both sulfur and phosphorus in its structure. b) protein has both sulfur and phosphorus in its structure. c) both DNA and protein have no phosphorus or sulfur in their structure. d) DNA has phosphorus, while protein has sulfur in its structure. Copyright Pearson Prentice Hall
DNA is a long molecule made of monomers called a) b) c) d) nucleotides. purines. pyrimidines. sugars. Copyright Pearson Prentice Hall
Chargaff's rules state that the number of guanine nucleotides must equal the number of • • cytosine nucleotides. adenine nucleotides. thymine plus adenine nucleotides. Copyright Pearson Prentice Hall
In DNA, the following base pairs occur: a) b) c) d) A with C, and G with T. A with T, and C with G. A with G, and C with T. A with T, and C with T. Copyright Pearson Prentice Hall
DNA • Two strands coiled called a double helix • Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO 4) groups by phosphodiester bonds • Center made of nitrogen bases bonded together by weak hydrogen bonds copyright cmassengale 30
DNA Nucleotide Phosphate Group O O=P-O O 5 CH 2 O N C 1 C 4 Sugar (deoxyribose) C 3 C 2 copyright cmassengale Nitrogenous base (A, G, C, or T) 31
5 DNA O 3 3 P 5 O O C G 1 P 5 3 2 4 4 P 5 P 2 3 1 O T A 3 O 3 5 O copyright cmassengale 5 P P 32
Nitrogenous Bases • Double ring PURINES Adenine (A) Guanine (G) A or G • Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C copyright cmassengale 33
Base-Pairings • Purines only pair with Pyrimidines • Three hydrogen bonds required to bond Guanine & Cytosine 3 H-bonds G copyright cmassengale C 34
Question: • If there is 30% Adenine, Adenine how much Cytosine is present? copyright cmassengale 35
DNA Replication 36
Replication Facts • DNA has to be copied before a cell divides • DNA is copied during the S or synthesis phase of interphase • New cells will need identical DNA strands 37
DNA REPLICATION • Semi-conservative = each one of the parent DNA strands is passed to the daugher DNA + one new strand for each • Semi-conservative DNA (30 secs) SNEAK PREVIEW: DNA REPLICATION PLAYERS (enzyme review)
Synthesis Phase (S phase) • When: S phase during interphase of the cell cycle • Where: Nucleus of eukaryotes S DNA replication takes place in the S phase G 1 interphase G 2 Mitosis copyright cmassengale -prophase -metaphase -anaphase -telophase 39
DNA Helicase • The enzyme is unwinding the chain and breaking the H-bonds between the complementary base pairs (A-T, G-C).
How Fast? • Prokaryotic DNA polymerase can work at about 1000 bases per second. • Eukaryotic DNA polymerase can work at about 50 bases per second.
Proofreading New DNA • DNA polymerase initially makes about 1 in 10, 000 base pairing errors • Enzymes proofread and correct these mistakes • The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors copyright cmassengale 42
RNA Replication
Steps of DNA Replication 1. Helicase breaks Hydrogen bonds separating the strands of DNA. 2. DNA Polymerase grabs free floating nucleotides to pair with complementary pairs. 3. Creating a semiconservative strand of DNA.
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