Cell Biology Quiz: Bacterial Structures and Functions

Microbes

• Microbiology is the study of microbes, organisms too small to be seen with the naked eye.
• Microbes include bacteria, viruses, fungi, and protozoa.
• Infectious diseases are a major cause of death worldwide, with microbes being responsible for approximately 26% of global deaths (15 million per year).

Importance of Microbes

• Microbes are crucial for a variety of processes, including wastewater treatment, food production (e.g., brewing, baking, dairy), and medicine (e.g., antibiotics, amino acids, insulin, HGH).
• They also play a vital role in agriculture by enhancing soil fertility and plant growth, and combating pests.
• Understanding microbes is essential in fighting infectious diseases, developing treatments, and managing outbreaks.

Koch's Postulates

• A particular microorganism causes a specific disease.
• The causative microorganism must be present in every case of the disease, but absent from healthy organisms.
• The suspected microorganism must be isolated and grown in a pure culture.
• The cultured microorganism should cause the disease when introduced into a healthy host.
• The same microorganism must then be isolated again from the diseased host.

Microbiology Today

• Chemotherapy/antibiotics must be selectively toxic to the microbe, with minimal side effects on the host.
• Immunology involves vaccine development to prevent infectious diseases.
• Basic biology provides fundamental knowledge of micro organisms (e.g., metabolism and genetics).
• Genetic engineering and genomics are used to synthesize human proteins and develop gene therapies.

Types of Microscopy

• Electron microscopes have greater resolving power than light microscopes.
• Electron microscopes use beams of electrons, not light.
• Light microscopes use electromagnetic lenses.
• Samples for transmission electron microscopy (TEM) are held in a vacuum and the method views internal structures.
• Samples for scanning electron microscopy (SEM) are also held in a vacuum and the method views the surfaces of microbes.

Staining

• Simple stains make bacteria visible under microscopes, usually with a basic dye.
• Differential stains (e.g., Gram stain, Acid-fast stain) distinguish between different groups of bacteria based on differences in their cell wall structures.
• Special stains highlight specific cell structures (e.g., flagella, endospores).

Culturing Microorganisms

• Culturing microbes is needed to isolate pure cultures from mixed cultures, to study and isolate individual types.
• Different microbes have different nutritional needs for growth and culturing.
• Culture media can be liquid (broth) or solid (containing agar) and can be either defined or complex.

Media Types – Special Culture Media

• Enriched media supplement basal media with additional growth factors to enable growth of specific bacterial species.
• Differential media contain chemical indicators to visually distinguish between different species.
• Selective media contain substances that inhibit the growth of unwanted bacteria, promoting the growth of a specific group.

Bacterial Envelopes

• Mycobacterial envelopes, like that of Mycobacterium tuberculosis, offer a physical barrier to drugs.
• The outer membrane in Gram-negative bacteria, containing lipopolysaccharides, serves to protect the bacteria.
• The Gram-positive envelope has a thicker peptidoglycan cell wall.

Bacterial External Structures

• Pili are hairlike appendages that are used for attachment to other cells or surfaces.
• Flagella are corkscrew-shaped appendages that are used for motility.
• Capsules are substances on the outermost layer of the bacterial cell that enhance virulence factors.

Endospores

• Endospores are tough, dormant structures produced by some bacteria.
• Endospores can resist extreme heat, dehydration, chemicals, and radiation.

Archaea

• Archaea are prokaryotic organisms that evolved separately from bacteria.
• Although similar in structure to bacteria, some have unique biochemical features.

Extremophiles

• Thermophiles flourish in high-temperature environments.
• Methanogens thrive in anaerobic conditions (no oxygen).
• Halophiles survive in extremely salty environments.

Viral Taxonomy

• Viruses are classified based on their nucleic acid type (DNA or RNA), replication strategy, and morphology.

Viral Gene Expression

• Viruses utilize host cell machinery to replicate and produce components for new viruses.
• RNA viruses have diverse mechanisms depending on their type of RNA.

Viral Diseases

• Common viral diseases include AIDS/HIV, hepatitis (A-E), rabies, and influenza.
• Examples of other viral illnesses are chicken pox, EBV-associated cancers, and pneumonia.
• Viral diseases often have high mutability, which makes creating a vaccine for many a challenge (e.g., influenza).

Viral Transmission

• HIV transmission can occur via sexual contact, blood exposure, and from mother to child.

Bacterial Classification

• Traditional characteristics like morphology (shape & arrangement), biochemical tests (e.g., metabolism), physiological characteristics (e.g., temperature ranges), and serological tests (using antibodies) are used.
• Modern characteristics like comparing gene sequences (genetic material) are crucial for detailed bacterial classification.

Microbial Growth

• Microbial growth follows characteristic phases: lag, exponential, stationary, and death.
• Growth can be described through understanding doubling time and other factors.
• Microbes need various amounts and types of nutrients and other conditions to thrive.

Microbial Genetics

• DNA is the genetic material in cells and has vital functions in replication, transcription, and translation.
• Bacterial genetics differs from eukaryotic genetics in that the DNA is not encased in a nuclear membrane, plasmids are common, and additional genetic material may be present in their cells.
• Genes in bacteria usually grouped together into operons.
• Mutations occur in DNA and certain mutants are useful for experiments.

Genetic Exchange Among Bacteria

• Transformation, conjugation, and transduction are three common processes used by bacteria to acquire and exchange genetic information.
• Genetic diversity is crucial for bacteria to acquire necessary adaptations.

Microbial Metabolism

• Metabolism is the sum of all biochemical reactions and includes both catabolic and anabolic pathways.
• Microbes can be classified according to how they obtain energy and carbon from their environments (e.g., chemoheterotrophs, photoheterotrophs).

Microbial Genetics Methods

• Techniques for testing mutations, and selecting and obtaining mutants for study are discussed.