Microbiology Exam 1 Study Guide: Cell Structure, Metabolism, Sterilization, and Transport Mechanisms

Microbial Cell Structure and Pigments

Photosynthetic Pigments in Bacteria

Photosynthetic pigments are specialized molecules that capture light energy for photosynthesis in bacteria. These pigments are typically found in cyanobacteria and other photosynthetic bacteria.

• Chlorophylls: Main pigment in cyanobacteria and plants.

• Bacteriochlorophylls: Found in purple and green bacteria.

• Carotenoids: Accessory pigments that protect against photooxidative damage.

Example: Cyanobacteria use chlorophyll a for oxygenic photosynthesis.

Prokaryotic and Eukaryotic Cell Structure

Key Features of Prokaryotic Cells

Prokaryotic cells, such as bacteria and archaea, differ from eukaryotic cells in several ways:

• No membrane-bound nucleus

• Lack of membrane-bound organelles

• Cell wall composition (peptidoglycan in bacteria)

• Smaller ribosomes (70S)

Example: Escherichia coli is a typical prokaryote.

Microbial Classification by Oxygen Requirement

Types of Microorganisms Based on Oxygen Use

Microorganisms are classified by their oxygen requirements:

• Obligate aerobes: Require oxygen for growth.

• Obligate anaerobes: Cannot tolerate oxygen.

• Facultative anaerobes: Can grow with or without oxygen.

• Microaerophiles: Require low levels of oxygen.

• Aerotolerant anaerobes: Do not use oxygen but tolerate its presence.

• Thermophiles: Thrive at high temperatures.

• Psychrophiles: Thrive at low temperatures.

• Mesophiles: Prefer moderate temperatures.

Example: Clostridium species are obligate anaerobes.

Microbial Growth and Death

Growth Phases and Death Point

Bacterial populations undergo distinct growth phases:

• Lag phase: Adaptation, no division.

• Log phase: Rapid cell division.

• Stationary phase: Nutrient depletion slows growth.

• Death phase: Cell death exceeds division.

Thermal death point is the lowest temperature at which all cells in a culture are killed in 10 minutes.

Microbial Control: Sterilization and Disinfection

Methods of Sterilization

Sterilization is the process of eliminating all forms of microbial life, including spores.

• Autoclave: Uses steam under pressure (typically 121°C, 15 psi, 15-20 min).

• Chemical agents: Ethylene oxide, glutaraldehyde.

• Filtration: Removes microbes from liquids and air.

Limitations of autoclave: Not suitable for heat-sensitive materials.

Disinfectants act by disrupting plasma membranes, denaturing proteins, or oxidizing cellular components.

Antiseptics and Disinfectants

Common Agents and Their Uses

• Triclosan: Used in surgical hand scrubs.

• Alcohols: Effective against bacteria and viruses.

• Quaternary ammonium compounds: Used for surface disinfection.

Example: Iodine is used for skin disinfection before surgery.

Microbial Metabolism and Energy Production

Types of Metabolism

• Chemotrophs: Obtain energy from chemical compounds.

• Phototrophs: Obtain energy from light.

• Chemoheterotrophs: Use organic compounds for energy and carbon.

• Photoheterotrophs: Use light for energy, organic compounds for carbon.

Example: Rhodobacter species are photoheterotrophs.

Microbial Transport Mechanisms

Cell Transport and Diffusion

Cells use various mechanisms to move substances across membranes:

• Facilitated diffusion: Movement via membrane proteins, no energy required.

• Active transport: Requires energy (ATP) to move substances against a gradient.

• Simple diffusion: Passive movement down a concentration gradient.

• Aquaporins: Channel proteins for water transport.

• Extracellular enzymes: Break down large molecules for transport.

Example: Glucose uptake in bacteria often uses facilitated diffusion.

Additional Info

• Cyanobacteria: Oxygenic photosynthetic bacteria, important for global carbon and nitrogen cycles.

• Gram-positive vs. Gram-negative bacteria: Differ in cell wall structure and response to antibiotics.

• Food preservation methods: Include canning, pasteurization, irradiation, and chemical preservatives.