Chapter 8 Microbial Genetics 8.1 Prokaryotic DNA • Geologic time • Fossil evidence • Archaea domains • Microbial evolution FIGURE 1: Fossil microbes Courtesy of Abigail Allwood, Geologist at NASA Jet Propulsion Laboratory Time-Line of Life on Earth FIGURE 2: The appearance of life on Earth 8.1 DNA and Chromosomes History: The Tortoise and the Hare • Deciphering the structure of DNA • Rosalind Franklin (tortoise) • James Watson (the hare) working with Francis Crick FIGURE MF01: Photo of Rosalind Franklin © Vittorio Luzzati/Photo Researchers, Inc. • Bacterial and Archaeal DNA is organized within the nucleoid. • The DNA exists as a single, circular chromosome. • DNA within a chromosome is highly compacted. • Many microbial cells also contain plasmids. • Plasmids carry nonessential but often useful information. FIGURE 4a: DNA packing 8.2 DNA Replication • Highly regulated process: • Initiation • Elongation • Termination • Leading strand and lagging strand Figure 05: Replication of Circular Chromosome in E. coli. 8.3 Protein Synthesis • Central dogma identifies the flow of genetic material (DNA RNA protein). • Transcription copies genetic information into RNA. FIGURE 7: The central dogma 8.3 Protein Synthesis • Types of RNA • mRNA • tRNA • rRNA Figure 11: The Transcription of the Three Types of RNA. A Comparison of DNA and RNA Figure T02: A Comparison of DNA and RNA. The Transcription Process • Transcription - gene DNA serves as a template for new mRNA molecules Figure 08: The Transcription Process. The Genetic Code is Degenerate • The genetic code consists of 3 letter words. • More than one codon specifies a specific amino acid. Figure T03: The Genetic Code Decoder. Translation is the process of making the polypeptide at the ribosome. • Chain initiation • Chain elongation • Chain termination/ release Figure 12A: Protein Synthesis in a Bacterial Cell. Concept Map for Protein Synthesis Figure 16: A Concept Map for Protein Synthesis. • Many antibiotics interfere with protein synthesis. • Proteins synthesis can be controlled in several ways. • Transcription and translation are compartmentalized. Protein synthesis can be controlled in several ways. FIGURE 14: The operon and negative control 8.4 Mutations – as a result of heritable, permanent changes in the DNA • Mutations can be spontaneous or induced. • Physical mutations • Chemical mutagens Figure 17: Ultraviolet Light and DNA The Effect of Chemical Mutagens Figure 18A: The Effect of Chemical Mutagens. Categories and Results of Point Mutations • Point mutations are a result of spontaneous or induced mutations. • Base-pair substitutions • Base-pair deletion or insertion Figure 19: Categories and Results of Point Mutations. • Repair mechanisms attempt to correct mistakes or damage in the DNA. • Cells have the ability to repair damaged DNA. • Mismatch repair • Excision repair FIGURE 21: Excision repair mechanism FIGURE 20: Mismatch repair mechanisms • Transposable genetic elements can cause mutations. • Barbara McClintock discovered transposons in maize. • Insertion sequences and transposons move from one DNA location to another. FIGURE 22: Transposon "jumping" and structure 8.5 Identifying Mutants – an organism carrying a mutation • Plating techniques select for specific mutants or characteristics. • The Ames test can identify potential mutagens. FIGURE 25: Using the Ames test Positive Selection of Mutants Figure 24: Positive Selection of Mutants.