Microbiology Chapter 8 Study Guide

Genetic Change in Bacteria

• Genetic changes can occur through transformation, mutation, conjugation, and transduction.
• Transformation involves uptake of "naked" DNA from the environment.
• Conjugation requires direct cell-to-cell contact and is a form of horizontal gene transfer.
• Transduction transfers bacterial DNA via bacteriophage.

UV-Induced DNA Damage

• UV light causes thymine dimers, where adjacent thymine bases on DNA strands covalently bond.

Structure of DNA

• DNA consists of two antiparallel nucleotide strands forming a double helix.
• The backbone is made of deoxyribose and phosphate groups, with hydrogen bonds between A-T and C-G pairs.

DNA Replication

• DNA replication occurs in one direction on the bacterial chromosome.
• DNA polymerase synthesizes the new strand, using RNA primers and adding nucleotides in the 5' to 3' direction.
• The leading strand is synthesized continuously, while the lagging strand forms Okazaki fragments.

Types of Enzymes and DNA Repair

• Inducible enzymes are produced in response to specific substrates.
• Repair processes may involve a race between endonuclease and methylase.
• Mutation is a permanent alteration in DNA sequence while mutagens are agents causing mutations.

Gene Definitions and Functions

• A gene is a nucleotide sequence that codes for a functional product.
• Genetics encompasses the study of gene information, expression, and replication.
• The genome contains all genetic information in a cell at any time.

Genotype vs. Phenotype

• Genotype refers to the organism's genetic makeup, while phenotype is the observable expression of genes.

Exons and Introns

• Exons are DNA regions coding for proteins, while introns are non-coding regions.

Central Dogma of Molecular Biology

• The flow of genetic information is described as DNA → RNA → Protein.

Protein Synthesis Process

• Transcription copies DNA into mRNA, which is then modified in eukaryotes before translation into proteins.

Gene Regulation

• Pre-transcriptional control includes repression (inhibiting expression) and induction (activating expression).
• Post-transcriptional control involves mechanisms such as riboswitches and microRNAs to regulate gene expression.

Mutation and Repair

• Mutations can have neutral, beneficial, or harmful effects and occur spontaneously at rates of 1 in 10^9 for base pairs.
• Mutation repair can involve several mechanisms depending on the type of mutation.

Selection Methods for Mutants

• Direct (positive) selection identifies mutants by their growth or appearance, while indirect (negative) selection identifies mutants that lack certain functions.

Plasmids and Transposons

• Plasmids can carry traits like antibiotic resistance and enzymes for unique compound metabolism.
• Transposons can move DNA segments within a genome and include sequences for cutting and resealing DNA.

Gene Transfer Mechanisms

• Vertical gene transfer involves inheritance between generations, while horizontal gene transfer occurs between cells of the same generation.
• Transformation, conjugation, and transduction are key mechanisms of horizontal gene transfer, each with unique processes.

Recombination in Bacteria

• Transformation involves uptake of naked DNA; conjugation requires direct contact; and transduction involves DNA transfer via bacteriophages.