BIOL 2210 Midterm Exam I: Microbiology Core Concepts and Applications

Section 1: The Microbial World and You

Spontaneous Generation and Pasteur's Experiment

Understanding the origin of microorganisms and the refutation of spontaneous generation is foundational in microbiology.

• Spontaneous Generation: The hypothesis that living organisms arise from nonliving matter.

• Pasteur's Experiment: Demonstrated that bacteria grow only when media is contaminated with bacteria, disproving spontaneous generation.

• Key Point: Only media that had been in contact with bacteria showed growth.

• Example: Pasteur's swan-neck flask experiment prevented airborne microbes from contaminating sterile broth.

Chemical Principles

Covalent Bonds and Molecular Interactions

Chemical bonds are essential for molecular structure and function in biological systems.

• Covalent Bond: A bond formed by the sharing of electrons between atoms.

• Resonance: Occurs when electrons are delocalized over two or more atoms, stabilizing the molecule.

• Hydrogen Bond: A weak bond between a hydrogen atom and an electronegative atom (e.g., N or O).

• Example: Hydrogen bonds are critical in water's properties and in stabilizing DNA structure.

Water and Its Properties

Water's polarity and hydrogen bonding make it a universal solvent and influence biological processes.

• Hydrogen Bonding: Water molecules stick together due to hydrogen bonds, resulting in high surface tension.

• Example: Water beads on a surface due to cohesion from hydrogen bonding.

Observing Microorganisms Through a Microscope

Microscopy Techniques

Microscopy is vital for visualizing microorganisms and understanding their structure.

• Types of Microscopes:

  • Transmission Electron Microscope (TEM): Used for viewing internal structures of thin specimens.

  • Scanning Electron Microscope (SEM): Used for viewing surface structures.

  • Dark Field Microscopy: Views specimens with light reflected off the specimen, enhancing contrast.

  • Bright Field Microscopy: Standard light microscopy for stained or naturally pigmented specimens.

• Hydrogen Bond Donor: In a molecule, the N-H bond can serve as a hydrogen bond donor.

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Cell Structure and Membranes

Cell membranes are composed of phospholipids, proteins, and other molecules that regulate transport and cellular integrity.

• Phospholipid Bilayer: Consists of hydrophilic heads and hydrophobic fatty acid tails.

• Fatty Acid Component: The hydrophobic region of the membrane, represented by the tails in diagrams.

• Capsules and Slime Layers: External structures that protect bacteria and aid in adherence, but do not build flagella.

Transport Proteins and Endosymbiosis

Transport proteins facilitate movement of molecules across membranes, and endosymbiosis explains the origin of some organelles.

• Porins: Proteins that form channels in the outer membrane of Gram-negative bacteria.

• Endosymbiosis: Theory that mitochondria and chloroplasts originated from engulfed prokaryotes.

Microbial Metabolism

Enzyme Function and Inhibition

Enzymes catalyze biochemical reactions, and their activity can be regulated by inhibitors.

• Competitive Inhibitor: Molecule that binds to the active site of an enzyme, blocking substrate binding.

• Condensation Reaction: A chemical reaction where two molecules combine with the loss of a small molecule (often water).

• Example: Formation of peptide bonds during protein synthesis.

Phosphorylation Mechanisms

Phosphorylation is a key process in energy transfer and metabolic regulation.

• Phosphorylation: Addition of a phosphate group to a molecule, often regulating activity or enabling energy transfer.

• Phosphorylation in Bacteria: Used to create a proton gradient and regulate ATP synthesis.

• Equation: $\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

Microbial Growth

Culture Media and Growth Conditions

Microbial growth depends on nutrient availability and environmental conditions.

• Defined and Selective Media: Media with known chemical composition and selective agents to favor growth of specific microbes.

• Continuous Culture: Maintains cells in exponential growth phase, useful for industrial and research applications.

• Example: Chemostat used for continuous culture.

Environmental Adaptations

Microorganisms adapt to various environments through specialized mechanisms.

• Osmotic Pressure: Bacteria regulate internal solute concentration to survive in hypotonic or hypertonic environments.

• Storage Granules: Bacteria store nutrients such as glycogen or polyphosphate for later use.

Microbial Genetics and Biotechnology

RNA and Protein Synthesis

Genetic information is stored in DNA and expressed through RNA and protein synthesis.

• RNA Viruses: Some viruses have RNA genomes and do not encode a protein coat.

• Gene Expression: Involves transcription of DNA to RNA and translation of RNA to protein.

Control of Microbial Growth

Staining and Identification

Differential staining techniques help identify and classify microorganisms.

• Gram Stain: Differentiates bacteria based on cell wall composition.

• Acid-Fast Stain: Identifies bacteria with mycolic acid in their cell walls, such as Mycobacterium.

Tables

Ingredients for a Biological Medium

The following table lists the components of a defined medium used for microbial growth.

Component	Amount
K2HPO4	6 grams
KH2PO4	3 grams
NaCl	0.5 grams
MgSO4	0.1 grams
Glucose	1 gram
Yeast extract (vitamins)	1 mg/liter

Additional info:

• Some questions reference advanced topics such as the proton motive force (PMF), endosymbiosis, and specialized transport proteins, which are covered in chapters on cell structure, metabolism, and genetics.

• Questions on microscopy and staining techniques align with chapters on observing microorganisms and microbial growth control.

• Comparisons between prokaryotic and eukaryotic cells, as well as environmental adaptations, are central to understanding microbial diversity and physiology.