Chapter 8 micro

McGraw Hill Education

  • Fourth Edition Microbiology Fundamentals: A Clinical Approach by Marjorie Kelly Cowan and Heidi Smith.

  • Extensive COVID-19 content included.

Chapter 8: Microbial Genetics and Engineering

Introduction to Genetics and Genes

  • Genetics: Study of inheritance (heredity) of living things, covering:

    • Transmission of biological traits from parent to offspring.

    • Expression and variation of traits.

    • Structure and function of genetic material.

  • Genome: Total genetic material of an organism, including chromosomes, plasmids, and/or RNA.

The Nature of Genetic Material

  • Chromosomes: Discrete cellular structures made of DNA.

    • Eukaryotic Chromosomes:

      • DNA is wound around histones.

      • Located in the nucleus.

      • Can be diploid (in pairs) or haploid (single).

      • Linear appearance.

    • Bacterial Chromosomes:

      • Typically circular and single.

      • Packaged with proteins similar to histones.

Genes

  • Defined as recipes for proteins.

  • Three categories of genes:

    • Structural Genes: Code for proteins.

    • RNA Machinery Genes: Code for RNA involved in protein production.

    • Regulatory Genes: Control gene expression.

  • Genotype: Organism's genetic makeup.

  • Phenotype: Expression of traits influenced by genotype and environment.

The DNA Molecule

  • Nucleotides: Basic DNA unit, consisting of:

    • Phosphate.

    • Deoxyribose sugar.

    • Nitrogenous bases.

  • Nucleotides form sugar-phosphate backbone of DNA strands.

  • Bases are held together by hydrogen bonds.

Helix Structure

  • Antiparallel Arrangement: One helix side runs 5’ to 3’, the other runs 3’ to 5’.

  • Base Pairing Rules:

    • Adenine (A) pairs with Thymine (T).

    • Guanine (G) pairs with Cytosine (C).

DNA Replication

  • Semiconservative Replication:

    • Parent strand unwinds via DNA helicase.

    • New strands form through complementary base pairing with DNA polymerase.

    • DNA ligase seals breaks in the sugar-phosphate backbone.

    • Resulting DNA molecule is half old, half new.

Enzymes in DNA Replication

  • Helicase: Unzips DNA helix.

  • Primase: Synthesizes an RNA primer.

  • DNA Polymerase III: Adds bases and proofs the chain.

  • DNA Polymerase I: Removes primers, closes gaps, and repairs mismatches.

  • Ligase: Final binding of nicks in DNA.

  • Topoisomerases I and II: Manage supercoiling and untangling.

Gene Expression

  • Information Flow: DNA → RNA → Protein.

  • Transcription: DNA template used to make mRNA.

  • Translation: mRNA directs amino acid sequence; assisted by rRNA and tRNA.

RNA Structure

  • RNA: Ribonucleic acid, single-stranded, with ribose sugar and uracil instead of thymine.

  • Three major types of RNA:

    • Messenger RNA (mRNA): Carries genetic information.

    • Transfer RNA (tRNA): Brings amino acids.

    • Ribosomal RNA (rRNA): Component of ribosomes.

Regulatory RNAs

  • Include micro RNAs, anti-sense RNAs, riboswitches, and small interfering RNAs.

  • Ribozymes: Remove unneeded RNA sequences.

Transcription Process

  • Regulated by primers, proteins, and regulatory RNAs.

  • Complementary RNA synthesized from DNA template.

  • RNA polymerase unwinds and unzips DNA.

Translation Process

  • Ribosomes: Made of protein and rRNA, varying in size between prokaryotes and eukaryotes.

  • Translation requires tRNA for amino acids; anticodon pairs with mRNA codon.

  • Ribosomes assemble amino acids into proteins.

The Master Genetic Code

  • Codon: Three nucleotide groups dictating amino acid addition; 64 triplet codes for 20 amino acids.

Eukaryotic vs. Bacterial Transcription and Translation

  • Eukaryotic mRNA processes one gene at a time; transcription and process occur in the nucleus.

Genetic Regulation of Protein Synthesis

  • Control mechanisms active only when genes are needed.

  • Found in bacteria, archaea, and eukaryotes through mechanisms such as operons, antisense RNAs, and micro RNAs.

The Lactose Operon

  • Model system for genetic induction control; features:

    • Regulator: Gene coding for protein to repress operon.

    • Control Locus: Contains promoter for RNA polymerase and operator as on/off switch.

Phase Variation

  • Bestows phenotypic changes via environmental influence, relevant to traits affecting bacterial envelope or pathogenicity.

Mutations

  • Original source of genetic variation; caused by replication errors, transposons, and mutagens.

  • Includes beneficial, harmful, or neutral changes; can be inherited.

Horizontal Gene Transfer

  • DNA transfer acquiring new genes, common in bacteria and fungi.

  • Plasmids: Circular DNA replicating independently, carrying useful traits.

  • Chromosomal Fragments: Integrated into chromosomes for replication.

DNA Recombination Events

  • Genetic recombination in bacteria increases variation by:

    • Conjugation: Transfer via direct connection.

    • Transformation: DNA absorption into the microbe's genome.

    • Transduction: Bacteriophage carries DNA from donor to recipient.

Transposons

  • Jumping genes capable of relocating within the genome, influencing gene expression.

Recombinant DNA Technology

  • Combines genetic material from different organisms; involves gene identification, cloning, excising, and insertion into vectors.

Polymerase Chain Reaction

  • Rapidly amplifies DNA without culturing, increasing amounts from few copies to billions in hours.

Enzymes in DNA Splicing

  • Restriction Endonucleases: Recognize and cleave foreign DNA, aiding biotechnological applications.

Analysis of DNA

  • Gel Electrophoresis: Produces readable DNA patterns, creating genetic fingerprints, and identifying genetic sequences.

Applications of Recombinant DNA Technology

  • Mass production of proteins, hormones, enzymes, and vaccines via genetic engineering.

Genetic Techniques to Treat Disease

  • Gene Therapy: Delivers functional gene copies into defective cells using retrovirus vectors.

  • CRISPR: Cuts and splices DNA to introduce desired genes.

Learning Outcomes

  • Define genome and gene; differentiate between genotype and phenotype; summarize bacterial DNA replication; describe transcription and protein synthesis; outline relationships among DNA, RNA, and proteins; explain recombinant organism characteristics; describe horizontal gene transfer methods; define mutation with examples; outline gene cloning processes; and name two disease treatment techniques.