Bacterial Cell Structure and Function – Study Guide (Chapter 3)

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Living organisms share several fundamental characteristics that distinguish them from non-living matter.

Reproduction: The ability to produce offspring, either sexually or asexually.
Metabolism: The sum of all chemical reactions that occur within a cell, including catabolism and anabolism.
Responsiveness: The ability to sense and respond to environmental changes.
Growth: Increase in size and/or number of cells.

Cells are classified as either prokaryotic or eukaryotic based on their structural features.

Prokaryotic cells lack a true nucleus and membrane-bound organelles. Examples: Bacteria and Archaea.
Eukaryotic cells have a true nucleus and various membrane-bound organelles. Examples: Fungi, Protozoa, Plants, and Animals.

Bacteria possess various external structures that contribute to their survival and pathogenicity.

Glycocalyx: A viscous, gelatinous polymer external to the cell wall, composed of polysaccharide, polypeptide, or both.
Capsule: A well-organized, firmly attached glycocalyx. Functions include protection from phagocytosis and desiccation.
Slime layer: A loosely attached, unorganized glycocalyx. Aids in adherence to surfaces.
Biofilms: Communities of microorganisms attached to a surface, embedded in a self-produced matrix. Example: dental plaque.

Flagella are long, whip-like appendages that provide motility to many bacteria.

Flagellar arrangement: Monotrichous (single flagellum), lophotrichous (tuft at one end), amphitrichous (flagella at both ends), peritrichous (flagella all over).
Movement: Bacteria move by runs (straight movement) and tumbles (random changes in direction).
Taxic responses: Chemotaxis (movement toward/away from chemicals), phototaxis (light), magnetotaxis (magnetic fields).
Fimbriae: Short, hair-like structures for attachment.
Pili: Longer than fimbriae, involved in conjugation (DNA transfer).

The cell wall provides structural support and shape to bacterial cells.

Peptidoglycan: A polymer consisting of sugars and amino acids forming a mesh-like layer outside the plasma membrane.
Gram-positive bacteria: Thick peptidoglycan layer, teichoic acids present.
Gram-negative bacteria: Thin peptidoglycan layer, outer membrane with lipopolysaccharide (LPS).
Mycobacteria: Contain mycolic acid in their cell wall, making them acid-fast.

Peptidoglycan Structure:

Composed of repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked by peptide bridges.

Acid-fast stain is used to identify Mycobacteria due to their waxy cell wall.

Bacteria contain several internal structures essential for their survival and function.

Nucleoid: Region containing the bacterial chromosome (DNA), not membrane-bound.
Plasmids: Small, circular DNA molecules that replicate independently of the chromosome.
Ribosomes: Sites of protein synthesis. Bacterial ribosomes are 70S (composed of 50S and 30S subunits).
Inclusions: Reserve deposits of nutrients (e.g., glycogen, polyphosphate granules).
Endospores: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium) for survival under adverse conditions.

Endospores are specialized structures that allow bacteria to withstand extreme conditions.

Archaea are prokaryotes but differ significantly from bacteria in several aspects.

Cell wall composition: Archaea lack peptidoglycan; may have pseudopeptidoglycan or proteinaceous walls.
Membrane lipids: Ether-linked in Archaea, ester-linked in Bacteria.
Ribosomes: Archaea have 70S ribosomes but with different protein and rRNA composition.

Eukaryotic cells contain membrane-bound organelles and a true nucleus.

Nucleus: Contains genetic material (DNA) enclosed by a nuclear envelope.
Ribosomes: 80S (60S and 40S subunits), free or bound to endoplasmic reticulum.
Cytoskeleton: Network of protein filaments for cell shape and movement.

Staining is essential for visualizing and differentiating microorganisms under the microscope.

Gram stain: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink/red).
Acid-fast stain: Identifies acid-fast organisms like Mycobacterium.

Feature	Gram-Positive	Gram-Negative	Acid-Fast (Mycobacteria)
Peptidoglycan Layer	Thick	Thin	Thin, with mycolic acid
Teichoic Acids	Present	Absent	Absent
Outer Membrane	Absent	Present (with LPS)	Absent
Stain Color	Purple	Pink/Red	Red (with acid-fast stain)

Example of capsule function: Streptococcus pneumoniae uses its capsule to evade phagocytosis.
Example of endospore-forming bacteria: Bacillus anthracis (anthrax), Clostridium botulinum (botulism).
Example of acid-fast bacteria: Mycobacterium tuberculosis.

Some questions in the original file refer to specific textbook figures and tables (e.g., Table 3.1, Fig. 3.21). For detailed diagrams, refer to your course textbook.
Concept mapping is a useful study tool for visualizing relationships between cell structures and their functions.