The Genetics of Microorganisms Chapter 8 The Genetics of Microorganisms

Figure 08.01: Fossil microbes. Geologic time Fossil evidence of early prokaryotes 3.8 BYA Archaea domains Microbial evolution Figure 08.01: Fossil microbes. Courtesy of Abigail Allwood, Geologist at NASA Jet Propulsion Laboratory

Time-Line of Life on Earth Figure 08.02: The appearance of life on Earth.

8.1 The Hereditary Molecule in All Organisms Is DNA Deciphering the structure of DNA Rosalind Franklin (tortoise) James Watson (the hare) working with Francis Crick Figured out that DNA is a double helix structure Figure MF08.01: Photo of Rosalind Franklin. © Vittorio Luzzati/Photo Researchers, Inc.

Figure 08.03: Genome Size Among the Bacteria and Archaea. Bacterial genome (complete set of genes) varies Figure 08.03: Genome Size Among the Bacteria and Archaea.

Bacterial and Archaeal DNA is organized within the nucleoid. The DNA usually 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 08.04A: DNA packing.

8.2 DNA Replication Occurs Before a Cell Divides Highly regulated process: Initiation Elongation Termination Leading strand and lagging strand Figure 08.05: Replication of Circular Chromosome in E. coli.

Semiconservative Replication of DNA Initiation starts at oriC DNA unwinds and strands separate with DNA helicase Takes place at replication fork Elongation DNA polymerase synthesizes new nucleotide strands of DNA on old template DNA polymerase only reads in the 3’ to 5’ direction for leading strand Lagging strand adds nucleotids with DNA ligase Termination codes for stop Figure 08.06: Replication Factory.

8.3 Gene Expression Produces RNA and Protein for Cell Function Central dogma identifies the flow of genetic material (DNA RNA protein). Transcription copies genetic information into complememtary RNA. Figure 08.07: The central dogma.

A Comparison of DNA and RNA Table 08.02: A Comparison of DNA and RNA.

Figure 08.11: The Transcription of the Three Types of RNA. 8.3 Protein Synthesis Types of RNA mRNA carries codon to ribosome tRNA carries anticodon and amino acid to ribosome rRNA together with proteins make up ribosomes Figure 08.11: The Transcription of the Three Types of RNA.

Figure 08.08: The Transcription Process During Elongation. Transcription - gene on DNA serves as a template for new mRNA molecules RNA polymerase reads the DNA template Promoter starts transcription Terminator ends it Figure 08.08: The Transcription Process During Elongation.

The Genetic Code is Degenerate The genetic code consists of 3 letter words. Code is redundant, more than one codon specifies a specific amino acid. Table 08.03: The Genetic Code Decoder.

Translation is the process of making the polypeptide at the ribosome. Chain initiation Chain elongation Chain termination/ release Figure 08.12A: Protein Synthesis in a Bacterial Cell.

Figure 08.16: A Concept Map for Protein Synthesis. Many antibiotics interfere with protein synthesis. Figure 08.16: A Concept Map for Protein Synthesis.

Gene expression can be controlled in several ways. An Operon consists of a regulatory gene, promoter, structural genes and a repressor In Negative feedback too much product serves as a repressor and turns off the gene Figure 08.14: The operon and negative control.

Transcription and translation are localized. Figure 08.15AB: The Localization of Transcription and Translation. Courtesy of Dr. Peter Lewis; School of Environmental and Life Sciences, University of Newcastle

8.4 Mutations Are Permanent Changes in a Cell’s DNA Mutations are the result of heritable changes in a genome Mutations can be spontaneous or induced. Physical mutations Chemical mutagens Figure 08.17: Ultraviolet Light and DNA.

The Effect of Chemical Mutagens Figure 08.18A: The Effect of Chemical Mutagens.

Categories and Results of Point Mutations Point mutations can affect protein structure and function. Base-pair substitutions silent mutation – no change due to redundancy missence mutation – wrong amino acid Nonsense mutation – stop codon Base-pair deletion or insertion Figure 08.19: Categories and Results of Point Mutations.

Figure 08.21AB: Transposon "jumping" and structure. Transposable genetic elements can cause mutations. Barbara McClintock discovered transposons in maize. Insertion sequences and transposons move from one DNA location to another. Figure 08.21AB: Transposon "jumping" and structure.

8.5 Techniques Exist for Identifying Mutants Plating techniques select for specific mutants or characteristics. The Ames test can identify potential mutagens. Mutagens cause revertants seen on medium lacking histidine Figure 08.24: Using the Ames test.

Figure 08.22: Negative Selection Identifies Auxotrophs. Negative selection is used to detect nutritional mutants that fail to grow on minimal media, when plated on complete nutritional medium Figure 08.22: Negative Selection Identifies Auxotrophs.

Figure 08.23: Positive Selection of Mutants. Positive Selection of Mutants shows resistant organisms growing on minimal medium Figure 08.23: Positive Selection of Mutants.