Microbiology Exam 1 Study Guide: Core Concepts and Processes

Microbiology Exam 1 Study Guide

Overview

This study guide outlines the key topics and concepts that will be covered on the first exam for a college-level Microbiology course. The exam will assess understanding of microbial diversity, structure, metabolism, energetics, and ecological roles, as well as the ability to apply biochemical and physiological principles to microbial systems.

Microbial Diversity and Classification

Importance of Microorganisms in Environmental Engineering

• Microorganisms play crucial roles in environmental engineering by facilitating processes such as soil nutrient cycling, biodegradation, bioremediation, and wastewater treatment.

• They are involved in metabolic diversity, including chemoautotrophy, photoautotrophy, and heterotrophy.

• Examples: Nitrosomonas in nitrification, Pseudomonas in pollutant degradation.

Classification of Microorganisms

• Microorganisms can be classified by carbon and energy source (e.g., autotrophs vs. heterotrophs, phototrophs vs. chemotrophs), cell structure (prokaryotes vs. eukaryotes), nucleic acid sequencing, cell shape, temperature requirements, oxygen requirements, and tolerance of extreme conditions.

• Major groups: Bacteria, Archaea, Viruses, Fungi, Protozoa, Algae.

• Example: Thermus aquaticus is a thermophilic bacterium used in PCR.

Prokaryotes vs. Eukaryotes

• Prokaryotes (Bacteria and Archaea) lack a membrane-bound nucleus and organelles, while eukaryotes (fungi, protozoa, algae) possess these structures.

• Prokaryotes typically have a single circular chromosome; eukaryotes have multiple linear chromosomes.

• Cell wall composition differs: peptidoglycan in bacteria, pseudopeptidoglycan in archaea, cellulose or chitin in eukaryotes.

Microbial Structure and Function

Cell Structure and Function

• Key components: cell wall, cell membrane, cytoplasm, nucleoid/nucleus, ribosomes, flagella, pili, capsules.

• Cell wall provides structural support and shape; cell membrane regulates transport; flagella enable motility.

• Differences in cell wall structure distinguish Gram-positive (thick peptidoglycan, teichoic acids) from Gram-negative (thin peptidoglycan, outer membrane with lipopolysaccharide) bacteria.

Genetic Variation and Evolution

• Microbial evolution is driven by mutations, random variation, adaptation, and selection.

• Genetic diversity enables survival in changing environments.

• Horizontal gene transfer (transformation, transduction, conjugation) accelerates adaptation.

Microbial Metabolism and Energetics

Redox Reactions and Energy Generation

• Microorganisms obtain energy through redox reactions (oxidation-reduction), transferring electrons from donors to acceptors.

• Key terms: oxidation (loss of electrons), reduction (gain of electrons).

• Energy yield depends on the difference in reduction potential ($\Delta E_0'$) between donor and acceptor.

• Formula: $\Delta G^0' = -nF\Delta E_0'$

• Example: Aerobic respiration uses O2 as the terminal electron acceptor; denitrification uses NO3-.

ATP and Energy Carriers

• ATP (adenosine triphosphate) is the universal energy currency of the cell.

• High-energy phosphate bonds in ATP store and release energy for cellular processes.

• Other carriers: NADH, NADPH, FADH2.

• ATP is produced via substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.

Electron Transport and Chemiosmosis

• Electron transport chains (ETC) transfer electrons through a series of carriers, generating a proton motive force (PMF) across membranes.

• PMF drives ATP synthase to produce ATP from ADP and inorganic phosphate.

• Reverse electron transport is used by some chemolithotrophs to generate reducing power (NADPH) for biosynthesis.

Microbial Growth and Survival

Adaptation to Environmental Stress

• Microorganisms adapt to harsh conditions (e.g., nutrient limitation, extreme pH, temperature, salinity) by forming spores, altering membrane composition, or producing stress proteins.

• Examples: Endospore formation in Bacillus and Clostridium.

Transport Mechanisms

• Cells transport compounds via diffusion, facilitated diffusion, active transport, and group translocation.

• Active transport requires energy (often from ATP or PMF).

• Example: Uptake of glucose via the phosphotransferase system (PTS).

Biochemical and Ecological Methods

Measuring Microbial Activity

• Methods include BOD (biochemical oxygen demand) tests, aggregate organic carbon measurements, and stoichiometric equations for metabolic processes.

• BOD measures the amount of oxygen consumed by microorganisms during the decomposition of organic matter.

• Formula for BOD calculation: $\text{BOD} = (\text{DO}_\text{initial} - \text{DO}_\text{final})$

• Limitations: BOD does not distinguish between different types of organic matter or microbial communities.

Stoichiometry of Microbial Processes

• Stoichiometric equations describe the balance of reactants and products in microbial metabolism.

• Example: Aerobic oxidation of glucose: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2 \rightarrow 6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O}$

• Stoichiometry is used to predict yields of biomass, energy, and byproducts.

Metabolic Pathways and Biogeochemical Cycles

Citric Acid Cycle (TCA Cycle)

• The citric acid cycle is central to both energy metabolism and biosynthesis.

• It oxidizes acetyl-CoA to CO2, generating NADH and FADH2 for the electron transport chain.

• Key intermediates are used for biosynthetic pathways.

TEAP Zones and Environmental Redox

• TEAP (Terminal Electron Accepting Process) zones refer to the stratification of electron acceptors in environments (e.g., O2, NO3-, Fe(III), SO42-, CO2).

• Microbial communities are structured according to available electron acceptors.

• Example: In sediments, aerobic respiration occurs near the surface, followed by denitrification, iron reduction, sulfate reduction, and methanogenesis at greater depths.

Summary Table: Gram-Positive vs. Gram-Negative Bacteria

Feature	Gram-Positive	Gram-Negative
Cell Wall	Thick peptidoglycan, teichoic acids	Thin peptidoglycan, outer membrane with LPS
Staining	Retains crystal violet (purple)	Counterstained (pink/red)
Periplasmic Space	Usually absent	Present
Examples	Bacillus, Staphylococcus	Escherichia coli, Pseudomonas

Additional info:

• Some content was inferred and expanded for academic completeness, such as detailed explanations of metabolic pathways, environmental adaptation, and the structure-function relationship in microbial cells.

• Specific equations and examples were added to clarify key biochemical and physiological processes relevant to the exam topics.