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Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth)

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Presentation on theme: "Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth)"— Presentation transcript:

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2 Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia Section 12-1 Figure 12–2 Griffith’s Experiment

3 Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia Section 12-1 Figure 12–2 Griffith’s Experiment

4 Avery and DNA Oswald Avery repeated Griffith’s work in an effort to determine which molecule in the heat-killed bacteria was important for transformation. Avery treated an extract made from heat-killed bacteria with enzymes that destroyed proteins, lipids, carbohydrates, RNA, and other molecules. Transformation still occurred. Avery repeated the experiments with enzymes that destroyed DNA. Transformation did not occur. DNA was the transforming factor. Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

5 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

6 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 Section 12-1 Figure 12–4 Hershey-Chase Experiment

7 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 Section 12-1 Figure 12–4 Hershey-Chase Experiment

8 The Components and Structure of DNA How could DNA do the three critical things that genes were known to do? Genes had to carry information from one generation to the next. Genes had to put that information to work by determining the heritable characteristics of organisms. Genes had to be easily copied, because all of a cell’s genetic information is replicated every time a cell divides.

9 PurinesPyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose Figure 12–5 DNA Nucleotides Section 12-1

10 Percentage of Bases in Four Organisms Section 12-1 Source of DNAATGC Streptococcus Yeast Herring Human Streptococcus Yeast Herring Human Chargaff’s Rules states that [A] = [T] and [G] = [C] in any sample of DNA.

11 Discovering the Role of DNA Rosalind Franklin (1952) – studies the DNA molecule using X-ray diffraction. Works with Maurice Wilkins. James Watson and Francis Crick (1953) – develop the double-helix model of the structure of DNA. They along with Maurice Wilkins win the Nobel Prize for their discovery. Sydney Brenner (1960) – along with other scientists shows the existence of messenger RNA. Walter Gilbert, Allan Maxam, and Frederick Sanger (1977) – develop the Sanger method to sequence DNA. Human Genome Project (2000) – the entire human genome is sequenced.

12 Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Figure 12–7 Structure of DNA Section 12-1

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14 Chromosome E. coli bacterium Bases on the chromosome Prokaryotic Chromosome Structure Section 12-2

15 Figure Chromosome Structure of Eukaryotes Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2

16 Figure 12–11 DNA Replication Section 12-2 Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand During replication the new nucleotides are added to the 3’ end of the new DNA strand. The deoxyribose is at the 3’ end and the phosphate group is at the 5’ end.

17 PurinesPyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose Figure 12–5 DNA Nucleotides Section ’ 3’

18 RNA and Protein Synthesis Genes are coded DNA instructions that control the production of proteins within the cell. The first step in decoding the DNA instructions is to copy part of the nucleotide sequence from DNA into RNA = TRANSCRIPTION. In most cases, an RNA molecule is a copy of a single gene. Like DNA, RNA consists of a long chain of nucleotides. Each RNA nucleotide has a 5-carbon sugar, a phosphate group, and a nitrogen base. In most cells, the primary job of RNA is protein synthesis.

19 Comparison of RNA and DNA RNADNA Sugar - riboseSugar - deoxyribose Usually single-strandedUsually double-stranded Nucleotides: adenine, cytosine, guanine, uracil Nucleotides: adenine, cytosine, guanine, thymine

20 fromtoto make up Types of RNA Section 12-3 also calledwhich functions toalso called which functions to can be RNA Messenger RNA Ribosomal RNA Transfer RNA mRNA Carry instructions for making a protein rRNA Combine with proteins tRNA bring amino acids to ribosome during translation and protein synthesis DNARibosomeRibosomes transcription made during

21 Transcription RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence of RNA. This process is called transcription and produces mRNA. RNA polymerase is the enzyme that carries out transcription. RNA polymerase binds to DNA and separates the DNA strands. One of the strands is then used as a template for the new strand of RNA. RNA polymerase binds to regions of DNA called promoters which have specific base sequences that act as a signal for where to start transcription. Similar sequences in DNA signal to the RNA polymerase to stop transcription.

22 RNA DNA RNA polymerase Figure 12–14 Transcription Section 12-3 Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only)

23 RNA Editing Eukaryotic genes contain introns and exons. The introns do not code for proteins. Exons code for proteins. When mRNA is made, both the introns and exons are copied from the DNA. The introns are cut out while the mRNA is still in the nucleus. The exons are then spliced together to form the final mRNA. Some mRNA may be cut and spliced in different ways to produce different mRNA molecules. This allows for a single gene to produce different forms of mRNA. Intron sequences may be involved in regulation of expression of genes.

24 Gene Structure & Protein Synthesis

25 The Genetic Code Proteins are made by joining amino acids into long chains called polypeptides. There are 20 different amino acids. The properties of the protein are determined by the order of amino acids. The genetic code is read three letters at a time so that each “word” is three bases long. Each three letter “word” is a codon. A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide. There are 64 possible codons. Some amino acids can be specified by more than one codon. There is a start codon, AUG (methionine). There are three stop codons.

26 Figure 12–17 The Genetic Code Section 12-3

27 Figure 12–18 Translation Section 12-3 Anticodon

28 Figure 12–18 Translation (continued) Section 12-3

29 Substitution Insertion Deletion Gene Mutations Section 12-4 Substitution Insertion Deletion Insertions and deletions are frameshift mutations.

30 Deletion Duplication Inversion Translocation Figure 12–20 Chromosomal Mutations Section 12-4

31 Regulatory sites Promoter (RNA polymerase binding site) Start transcription DNA strand Stop transcription Typical Gene Structure Section 12-5


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