Bacterial Cell Walls and Flagella

Study Notes

Gram-negative cell walls are thin, containing a thin peptidoglycan layer (5-10%) adjacent to the cytoplasmic membrane.
Gram-positive cell walls are thick, with a peptidoglycan layer forming almost 95% of the cell.

Flagella are extracellular bacterial cell structures responsible for bacterial motility.
The arrangement of flagella about the bacterial cell is unique to the species observed.
Common forms of flagella include:
- Monotrichous
- Lophotrichous
- Amphitrichous
- Peritrichous

Lag phase: a period of slow growth when cells adapt to the high-nutrient environment and prepare for fast growth.
Log phase: rapid exponential growth.
Stationary phase: caused by depleted nutrients, cells reduce metabolic activity and consume non-essential cellular proteins.
Death phase: bacteria run out of nutrients and die.

Aerobes (aerobic bacteria): grow only in the presence of oxygen.
Anaerobes (anaerobic bacteria): grow only in the absence of oxygen.
Facultative anaerobes (facultative anaerobic bacteria): grow in environments with or without oxygen.

Some bacteria are pathogenic (disease-causing) to plants and animals.
Bacteria can cause diseases through consumption of contaminated food and water, inhalation, and sexually transmission.

Bacteria contain a well-developed cell structure responsible for many of their unique biological functions.
Components of bacterial cells:
- Cell wall: outer covering of the cell that protects the bacterial cell and gives it shape.
- Cell membrane: surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.
- Cytoplasm: a gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.
- Nucleoid region: area of the cytoplasm that contains the single bacterial DNA molecule.
- Ribosomes: cell structures responsible for protein production.
- Plasmids: small independent pieces of DNA that can be easily gained or lost by a bacterium and can be transferred between bacteria.
- Flagella: long, whip-like protrusions that aid in cellular locomotion.
- Endospores: bacterial survival structures that are highly resistant to many different types of chemical and environmental stresses.
- Fimbriae: protein tubes that extend out from the outer membrane, facilitating the attachment of a bacterium to a surface.
- Pili: similar in structure to fimbriae but are much longer and present on the bacterial cell in low numbers, involved in the process of bacterial conjugation.