Morton Hall 4

Dr. Bradley Toler, a microbiologist from the Center for Marine Science, introduces the topic of cell structures.
Discusses his focus on archaea, particularly their impact on the nitrogen cycle, and the environments in which they are found.
Highlights the importance of the Dockett Center for Marine Science and suggests students visit.

Focus on:
- General concepts of cell biology for microbes
- Exterior cell structures, especially the cell membrane and cell wall
Mentioned key concepts about microbial size and microscopy to contextualize studies.

Microbes are the most dominant organisms on Earth, often too small to see without microscopy.
Comparisons are made:
- Visible objects range from grains of salt to human eggs.
- Examples of sizes include:
  - E. coli and mitochondria at micrometer scale to ribosomes and atoms at nanoscale.
Size range of different organisms:
- Bacteria and archaea: 0.1 microns to over 700 microns.
- Eukaryotic (animal) cells: 10-200 microns.
Benefits of smaller size:
- Higher surface area to volume ratio, facilitating nutrient uptake and survival in low-nutrient environments.

All cells share common features:
- Information storage (DNA/RNA)
- Structures (membranes, walls)
- Ribosomes for protein synthesis.
Eukaryotes possess a nucleus; prokaryotes have a nucleoid region.

Focus on:
- Cell membrane
- Cell wall (discussed later)
Key functions of these structures:
- Protect the cell
- Maintain shape and allow interactions with the environment.

Microbial shapes include:
- Coccus (spherical)
- Bacillus (rod-shaped)
- Spirillum (spiral)
- Variants and groupings of cells (e.g., streptococcus, staphylococcus).
Importance of morphology in diagnosis and understanding ecological community roles.

Emphasizes the importance of surface area:
- As cell size increases, surface to volume ratio decreases, impacting nutrient absorption efficiency.
Exercise analogy using a Rubik's cube to visualize how reducing size increases ratio.

Prokaryotes (bacteria and archaea) are uniquely structured:
- Information organized as a nucleoid without membrane-bound organelles.
- Ribosomes are key for protein assembly, with important implications for taxonomy and genetics.

All prokaryotic cells have a cytoplasmic membrane that acts as a barrier.
Structure includes:
- Phospholipid bilayer (polar head and hydrophobic tails)
- Proteins embedded for transport and signaling.
Differences between bacterial, archaeal, and eukaryotic membranes:
- Ester-linked phospholipids in bacteria versus ether-linked phospholipids in archaea.
- Some archaea have monolayer membranes for extreme environments.

Cells utilize transport proteins to move substances since diffusion alone is insufficient:
- Includes uniporters, antiporters, and symporters.
- Active transport such as simple transport and ABC transport mechanisms discussed.

Membranes are vulnerable to:
- Thermal stress and osmotic shocks (hypotonic vs. hypertonic environments).
- Chemical agents like detergents that destabilize the lipid bilayer.

Not all microbes have a cell wall, but for those that do, it provides:
- Protection against environmental stress and osmotic lysis.
- Structural rigidity primarily from peptidoglycan (glycan chains cross-linked with peptides).

Composed of:
- N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
- Unique linkages and forms (D and L amino acids), impacting antibiotic susceptibility.

Enzymes such as lysozyme target peptidoglycan, found in human tears and saliva.
Antibiotics like penicillin inhibit cell wall synthesis; effectiveness noted due to absence of peptidoglycan in human cells.
Resistance mechanisms evolving in microbes complicate treatment strategies.