Microbe Anatomy and Metabolism: Study Notes for Anatomy & Physiology

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Microbe Anatomy

Types of Microbes

Microbes are diverse microscopic organisms that include bacteria, archaea, fungi, protozoa, and algae. Understanding their classification is essential for studying their anatomy and physiology.

Bacteria: Prokaryotic cells lacking a nucleus; include cyanobacteria and other groups.
Archaea: Prokaryotic cells similar to bacteria but with distinct molecular features.
Eukarya: Eukaryotic cells with a nucleus; includes fungi, animals, plants, and protists.
Viruses: Acellular entities; not discussed in this section.

Key Point: Bacteria and Archaea are both prokaryotes, but differ in cell wall composition and membrane lipids. Example: Cyanobacteria are photosynthetic bacteria important in aquatic ecosystems.

Comparison of Microbial Domains

The three domains of life—Bacteria, Archaea, and Eukarya—can be compared based on cellular structure and genetic organization.

Feature	Bacteria	Archaea	Eukarya
Nucleus	No	No	Yes
Chromosome	Circular	Circular	Linear
Organelles	No	No	Yes
Ribosome Size	70S	70S	80S
Cell Wall	Peptidoglycan	Pseudopeptidoglycan	Cellulose/Chitin (if present)
Membrane Lipids	Ester-linked	Ether-linked	Ester-linked

Additional info: Archaea can have lipid monolayers and unique cell wall components.

Bacterial Cell Structure

Cell Surface Structures

Bacterial cells possess several surface structures that contribute to their function and pathogenicity.

Capsule: A rigid, firmly attached glycocalyx that increases virulence and protects against desiccation.
Slime Layer: A loosely attached, soft glycocalyx aiding in biofilm formation and surface attachment.
Cell Wall: Provides structural support; composed of peptidoglycan in bacteria.
Plasma Membrane: Selectively permeable barrier controlling entry and exit of substances.
Pili: Medium-length protein filaments used for motility, adhesion, and DNA transfer (conjugation).
Fimbriae: Short protein filaments for adhesion, often numerous on the cell surface.
Flagella: Long, whip-like structures enabling chemotaxis and motility; arrangement varies among species.

Example: Streptococcus pneumoniae uses its capsule to evade the host immune system.

Flagella Structure

Bacterial flagella are complex structures composed of three main parts:

Filament: Long, helical protein structure providing movement.
Hook: Connects the filament to the basal body.
Basal Body: Anchors the flagellum to the cell membrane and acts as a motor.

Key Point: Flagella arrangement (monotrichous, lophotrichous, peritrichous) affects bacterial motility.

Fimbriae and Pili

Fimbriae and pili are proteinaceous appendages found only in bacteria.

Fimbriae: Numerous, short filaments for adhesion to surfaces and biofilm formation.
Pili: Fewer, longer filaments for motility, adhesion, and horizontal gene transfer (conjugation).

Example: Neisseria gonorrhoeae uses pili for DNA exchange during conjugation.

Glycocalyx

The glycocalyx is a sugar/protein coating secreted by bacteria.

Capsule: Firmly attached, increases virulence.
Slime Layer: Loosely attached, aids in biofilm formation.
Functions: Prevents desiccation, promotes attachment, increases virulence.

Example: Streptococcus pneumoniae capsule is a key virulence factor.

Endospores

Endospores are highly resistant, dormant structures formed by some Gram-positive bacteria.

Function: Survival in harsh conditions (heat, desiccation, chemicals).
Not for reproduction: Endospore formation is a survival mechanism, not a reproductive process.
Life Cycle: Vegetative cell → endospore → vegetative cell.

Example: Bacillus anthracis forms endospores to survive in soil.

Bacterial Internal Structures

Cytoplasm and Genetic Material

The cytoplasm is the aqueous solution inside the plasma membrane containing essential cellular components.

Nucleoid: Region containing the bacterial chromosome (circular DNA).
Chromosome: Contains essential genes; larger than plasmids.
Plasmid: Optional, small circular DNA with non-essential genes; can confer antibiotic resistance.
Ribosomes: 70S ribosomes composed of 30S (small) and 50S (large) subunits; site of protein synthesis.

Additional info: Plasmids are important in genetic engineering and horizontal gene transfer.

Cell Inclusions

Bacteria store nutrients and resources in specialized inclusions.

Carbon Storage Polymers: Glycogen (sugar), poly-β-hydroxybutyric acid (PHB, lipid).
Metachromatic Granules: Inorganic phosphate reserves; used for identification (e.g., Corynebacterium diphtheriae).
Gas Vacuoles: Provide buoyancy in aquatic bacteria.
Magnetosomes: Magnetic particles that orient bacteria to Earth's magnetic field.

Example: Corynebacterium diphtheriae is identified by its metachromatic granules.

Microbe Metabolism

Enzymes and Metabolic Reactions

Metabolic reactions in microbes are catalyzed by enzymes, which lower activation energy and increase reaction rates.

Enzyme: Protein catalyst; not consumed in the reaction.
Substrate: Reactant(s) acted upon by the enzyme.
Activation Energy: Minimum energy required for a reaction to occur.
Enzyme Naming: Enzymes typically end in -ase (e.g., DNA polymerase).

Equation:

Enzyme Inhibition

Enzyme activity can be regulated by inhibitors, which are classified as competitive or non-competitive.

Competitive Inhibitor: Binds to the active site, blocking substrate binding; increasing substrate concentration can overcome inhibition.
Non-Competitive Inhibitor: Binds to an allosteric site, altering the active site shape; increasing substrate concentration does not overcome inhibition.

Type	Binding Site	Effect	Overcome by Substrate?
Competitive	Active Site	Blocks substrate	Yes
Non-Competitive	Allosteric Site	Alters active site	No

Additional info: Enzyme inhibitors are important in drug design and metabolic regulation.

ATP Production Pathways

Microbes generate ATP through various metabolic pathways, each with different energy yields.

Fermentation: Anaerobic process; yields 2 ATP per glucose.
Aerobic Respiration: Uses oxygen; yields up to ~38 ATP per glucose.
Anaerobic Respiration: Uses alternative electron acceptors; yields between 2 and 38 ATP per glucose.

Equation: Key Point: Aerobic respiration is the most efficient pathway for ATP production.

Summary Table: Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Chromosome	Circular	Linear
Organelles	Absent	Present
Ribosome Size	70S	80S
Cell Wall	Peptidoglycan (Bacteria), Pseudopeptidoglycan (Archaea)	Cellulose (Plants), Chitin (Fungi)

Additional info: This table highlights the principal differences between prokaryotic and eukaryotic cells relevant to microbe anatomy. ----------------------------------------