Bacterial & Archaeal Genetics | Chapter 9 – Brock Biology of Microorganisms (16th) скачать в хорошем качестве

Bacterial & Archaeal Genetics | Chapter 9 – Brock Biology of Microorganisms (16th)

Chapter 9 explores the genetic systems of Bacteria and Archaea, including how genetic variation arises through mutation and how DNA is exchanged via horizontal gene transfer mechanisms such as transformation, transduction, and conjugation. It also highlights modern discoveries like CRISPR-based immunity, transposable elements, and the use of gene transfer tools in research and biotechnology. ✅ Mutations and Genetic Variability 🔸 A mutation is a heritable change in DNA sequence 🔸 Mutants differ from the wild type; not all genotype changes alter phenotype 🔸 Spontaneous mutations: errors during DNA replication 🔸 Induced mutations: caused by chemicals, radiation, or biological agents 🔸 Types of mutations:  🔸 Point mutations (missense, nonsense, silent)  🔸 Frameshifts (insertion or deletion)  🔸 Transitions vs. transversions  🔸 Reversions: restore original phenotype (same-site or second-site)  🔸 Suppressor mutations: counteract primary mutation 🔸 Mutagenesis methods include base analogs, alkylating agents, UV radiation, and ionizing radiation 🔸 Cells have repair systems like the SOS response (error-prone but rescue mechanisms) ✅ Genetic Recombination and DNA Repair 🔸 Homologous recombination requires sequence similarity 🔸 Mediated by RecA protein and involves strand invasion and heteroduplex formation 🔸 Recombination produces genetic diversity and stabilizes foreign DNA 🔸 Complementation: wild-type gene introduced into mutant restores function 🔸 Partial diploid / merodiploid: cells carry duplicate gene copies ✅ Transformation (DNA Uptake) 🔸 Cells acquire free DNA from the environment 🔸 Requires competence, which can be natural or induced (e.g., electroporation) 🔸 Pili may mediate DNA uptake 🔸 DNA often degraded to single strand before entry 🔸 Stable integration requires homologous recombination via RecA ✅ Transduction (Phage-Mediated Transfer) 🔸 DNA transferred via bacteriophages 🔸 Generalized transduction: any gene may be transferred (lytic cycle error) 🔸 Specialized transduction: specific genes transferred when prophage excises incorrectly 🔸 Phage conversion: prophage alters host phenotype 🔸 Gene Transfer Agents (GTAs): virus-like elements packaging host DNA for exchange ✅ Conjugation (Plasmid-Mediated Transfer) 🔸 Requires cell-to-cell contact via conjugative pilus 🔸 F plasmid in E. coli encodes conjugation machinery 🔸 F+ cells (with plasmid) donate to F– cells (without plasmid) 🔸 Involves rolling circle replication: one strand transferred while replication occurs in both donor and recipient ✅ Hfr Strains and Chromosome Transfer 🔸 Hfr cells: F plasmid integrated into chromosome 🔸 Can transfer chromosomal genes during conjugation 🔸 Recipient remains F– unless entire F plasmid transfers (rare) 🔸 F′ plasmids carry chromosomal genes due to improper excision 🔸 Allows high-frequency gene transfer and mapping of chromosomal genes ✅ Gene Transfer in Archaea 🔸 Mechanisms include transformation, conjugation, and rare transduction 🔸 Conjugation may involve aggregation, pili, membrane vesicles, or nanotubes 🔸 Selectable markers differ from Bacteria due to unique envelope features ✅ Mobile DNA and Transposable Elements 🔸 Insertion sequences (IS elements): simplest, carry only transposase 🔸 Transposons: larger, carry additional genes (e.g., antibiotic resistance) 🔸 Transposition can be:  🔸 Conservative: excision and reinsertion  🔸 Replicative: creates a new copy 🔸 Used in mutagenesis and gene discovery 📘 Read full blog summaries for every chapter: https://lastminutelecture.com 📘 Have a book recommendation? Submit your suggestion here: https://forms.gle/y7vQQ6WHoNgKeJmh8 Thank you for being a part of our little Last Minute Lecture family! ⚠️ Disclaimer: These summaries are created for educational and entertainment purposes only. They provide transformative commentary and paraphrased overviews to help students understand key ideas from the referenced textbooks. Last Minute Lecture is not affiliated with, sponsored by, or endorsed by any textbook publisher or author. All textbook titles, names, and cover images—when shown—are used under nominative fair use solely for identification of the work being discussed. Some portions of the writing and narration are generated with AI-assisted tools to enhance accessibility and consistency. While every effort has been made to ensure accuracy, these materials are intended to supplement—not replace—official course readings, lectures, or professional study resources. Always refer to the original textbook and instructor guidance for complete and authoritative information.