Lecture Exam 2 Study Guide: Microbial Genetics, Recombinant DNA, Classification, and Eukaryotic Microbes

Chapter 8: Microbial Genetics

Nucleic Acids and Chromosomes

This section covers the structure and function of nucleic acids and the differences between prokaryotic and eukaryotic chromosomes.

• Nucleic acids are biomolecules (DNA and RNA) that store and transmit genetic information.

• Prokaryotic chromosomes are typically circular, lack histones, and are found in the nucleoid region, while eukaryotic chromosomes are linear, associated with histones, and located in the nucleus.

• Plasmids are small, circular DNA molecules found in prokaryotes that replicate independently of the chromosome.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA before cell division.

• Key enzymes: DNA polymerase, helicase, primase, ligase.

• Replication involves leading and lagging strands:

  • Leading strand: synthesized continuously in the 5' to 3' direction.

  • Lagging strand: synthesized discontinuously as Okazaki fragments.

• Prokaryotic DNA replication is typically bidirectional from a single origin; eukaryotes have multiple origins.

Transcription and Translation

Transcription is the synthesis of RNA from a DNA template; translation is the synthesis of proteins from mRNA.

• Transcription involves RNA polymerase creating mRNA, tRNA, and rRNA from DNA.

• Translation occurs at the ribosome, where mRNA codons are read to assemble amino acids into proteins.

• Key steps: initiation, elongation, termination.

• Genetic code is read in triplets (codons); each codon specifies an amino acid.

• Use of the genetic code/codon chart is essential for predicting amino acid sequences.

Gene Expression and Regulation

Gene expression is regulated to ensure proteins are produced only when needed.

• Operons (e.g., lac operon) are clusters of genes under control of a single promoter and operator, common in prokaryotes.

• Regulation can be positive (activators) or negative (repressors).

• Inducible operons (e.g., lac operon) are usually off but can be turned on; repressible operons (e.g., trp operon) are usually on but can be turned off.

Horizontal Gene Transfer

Horizontal gene transfer allows genetic material to move between organisms, contributing to genetic diversity.

• Transformation: uptake of naked DNA from the environment.

• Transduction: transfer of DNA by bacteriophages (viruses that infect bacteria).

• Conjugation: direct transfer of DNA via cell-to-cell contact, often involving plasmids (e.g., F factor in E. coli).

• Compare F+, F-, and Hfr cells in conjugation.

Transposons

Transposons are DNA sequences that can move from one location to another within the genome, causing mutations and gene rearrangements.

Chapter 9: Recombinant DNA Technology

Tools and Techniques

Recombinant DNA technology involves manipulating DNA to create new genetic combinations.

• Key tools: mutagens, reverse transcriptase, synthetic nucleic acids, restriction enzymes, vectors, gene libraries.

• Restriction enzymes cut DNA at specific sequences, allowing insertion of genes into vectors.

• Vectors (e.g., plasmids, viruses) carry foreign DNA into host cells.

Steps in Recombinant DNA Technology

• Isolate DNA of interest.

• Cut DNA with restriction enzymes.

• Insert DNA fragment into a vector.

• Introduce recombinant DNA into host cells (transformation, transduction, conjugation, or artificial methods like electroporation, protoplast fusion, and injection).

• Screen for successful recombinants (e.g., using selectable markers).

Applications

• Genomics: study of whole genomes.

• Production of vaccines and genetically engineered organisms (e.g., gene therapy, xenotransplants).

• Agricultural improvements (e.g., pest-resistant crops).

Chapter 10: Classification

Taxonomy and Domains of Life

Taxonomy is the science of classifying organisms. Modern classification uses genetic, biochemical, and morphological data.

• Three domains: Bacteria, Archaea, Eukarya.

• Major scientists: Carl Woese (proposed three-domain system).

• Classification methods: biochemical tests, serology, phage typing, nucleic acid analysis.

• Endospore formation is a key feature in some bacteria (e.g., Bacillus, Clostridium).

Comparing Domains

Feature	Bacteria	Archaea	Eukarya
Cell Type	Prokaryotic	Prokaryotic	Eukaryotic
Cell Wall	Peptidoglycan	No peptidoglycan	Varied (cellulose, chitin, none)
Membrane Lipids	Ester-linked	Ether-linked	Ester-linked
Examples	Escherichia coli	Halophiles, methanogens	Fungi, plants, animals

Chapter 12: Eukaryotic Microbes

Major Groups of Eukaryotic Microbes

This section reviews the characteristics of eukaryotic microorganisms, including protozoa, fungi, algae, helminths, and arthropod vectors.

• Protozoa: unicellular, motile, often aquatic; some cause diseases like malaria.

• Fungi: include yeasts and molds; can be dimorphic; reproduce sexually and asexually.

• Helminths: parasitic worms (e.g., platyhelminths, nematodes).

• Arthropods: insects and arachnids that can serve as disease vectors.

• Lichens: symbiotic associations between fungi and algae or cyanobacteria.

• Dinoflagellates: algae that can produce neurotoxins, causing paralytic shellfish poisoning.

Fungal Sexual Reproduction

• Plasmogamy: fusion of cytoplasm from two parent mycelia.

• Karyogamy: fusion of nuclei from the fused cells.

• Meiosis: production of haploid spores.

Transmission and Disease

• Mechanical and biological transmission of pathogens by insects.

• Protozoa and helminths can cause significant human diseases.

Key Characteristics for Identification

• Motility, cell structure, distribution, morphology, nutrition, and reproduction are important for classifying eukaryotic microbes.

Additional info: Some details, such as specific examples of operons, scientists, and disease-causing organisms, were inferred for completeness and clarity.