Microbial Genetics

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.

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

Figure 11: The Transcription of the Three Types of 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.

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.

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

9.1 Genetic Recombination in Prokaryotes Genetic information in prokaryotes can be transferred vertically and horizontally. Vertical gene transfer (VGT) is the transfer of genetic material from parent cell to daughter cell. Horizontal gene transfer (HGT) is the transfer of DNA from a donor cell to a recipient cell. FIGURE 2: Gene transfer mechanisms

Transformation is the uptake and expression of DNA in a recipient cell. By integration of a new DNA fragment, the recipient has gained some ability it previously lacked. Transformation was first described by Frederick Griffith in 1928.

Figure 03: The Transformation Experiments of Griffith

FIGURE 9.4: Transformation In a Gram-Positive Cell Competence is the ability of a recipient cell to take up DNA from the environment. It may give the recipient the ability to be more pathogenic. FIGURE 9.4: Transformation In a Gram-Positive Cell

FIGURE 9.5: Bacterial conjugation in E. coli Conjugation involves cell-to-cell contact for horizontal gene transfer. In conjugation, a donor cell (F+) transfers DNA directly to the recipient (F-). The donor cell forms a conjugation pilus to make contact with the recipient. FIGURE 9.5: Bacterial conjugation in E. coli © Dr. Dennis Kunkel/Visuals Unlimited

Conjugation also can transfer chromosomal DNA. High frequency of replication (Hfr) strains can donate chromosomal genes rather than just the F plasmid. The F factor attaches to the chromosome using an insertion sequence. FIGURE 6b: Conjugation

FIGURE 7: Bacteriophage replicative cycles Conjugation is usually interrupted before the entire chromosome is transferred. The recipient remains F- (called a recombinant F-). If an integrated F plasmid breaks from the chromosome, taking a fragment of chromosomal DNA, it is called an F' plasmid. FIGURE 7: Bacteriophage replicative cycles

9.2 Genetic Engineering and Biotechnology Genetic engineering was born from genetic recombination. Genetic engineering involves changing the genetic material in an organism to alter its traits or products. Biotechnology is the commercial and industrial products derived from genetic engineering. A recombinant DNA molecule contains DNA fragments spliced together from 2 or more organisms.

Figure 11: FDA Approvals of New Pharmaceutical Products. Data from: Biotechnology Information Institute (http://www.biopharma.com/approvals_2008.html)

Genetic engineering has many commercial and practical applications. The genes responsible for producing human insulin can be cloned into bacteria. Bacteria could be genetically engineered to: break down toxic wastes. produce antibiotics. Figure MI09B: The Sequence of Steps to Engineer the Insulin Gene into Escherichia coli Cells.

Figure 13: The Ti Plasmid as a Vector in Plant Genetic Plants have been engineered using microbial genes for: herbicidal activity. viral resistance. Cows produce more milk when injected with bovine growth hormone produced by engineered bacteria. Figure 13: The Ti Plasmid as a Vector in Plant Genetic Engineering.

Figure 12: Developing New Products Using Genetic Engineering.

Figure 15: Microorganism Genomes Sequenced. 9.3 Microbial Genomics Many microbial genomes have been sequenced. Hundreds of microbial genomes have been sequenced since the first in 1995, many of which are pathogens. Segments of the human genome may have “microbial ancestors.” As many as 200 of the 25,000 human genes are essentially identical to those of Bacteria. They were passed down from early ancestors of humans. Figure 15: Microorganism Genomes Sequenced.

It can help us identify microbes that cannot be cultured in the lab. Microbial genomics will advance our understanding of the microbial world. Knowing genomes of bacteria that cause food-borne diseases can help us: develop detection methods. make food safer. It can help us identify microbes that cannot be cultured in the lab. Environmental genomics helps us understand how microbial communities function. Biosensing will improve.