Microbiology Study Guide: Prokaryotes, Eukaryotes, Viruses, and Laboratory Techniques

Prokaryotic Cell Structures & Functions

Asexual Reproduction Methods

Asexual reproduction in prokaryotes allows for rapid population growth without the need for genetic recombination. The two main methods are:

• Binary Fission: The most common form of asexual reproduction in bacteria and archaea. The cell duplicates its DNA, elongates, and divides into two identical daughter cells.

• Budding: A process where a new cell develops from a protrusion (bud) on the parent cell, eventually detaching to become a separate organism. This is less common in prokaryotes.

Example: Escherichia coli reproduces by binary fission.

Archaea vs Bacteria: General Differences

Archaea and bacteria are both prokaryotes, but they differ in several fundamental ways:

• Cell Wall Composition: Bacteria have peptidoglycan in their cell walls; archaea do not.

• Membrane Lipids: Archaea have ether-linked lipids; bacteria have ester-linked lipids.

• Genetic Machinery: Archaea's transcription and translation processes are more similar to eukaryotes than to bacteria.

• Habitat: Archaea often inhabit extreme environments; bacteria are found in a wide range of environments.

Extremophile Terminology

Extremophiles are organisms that thrive in extreme environmental conditions. Types include:

• Thermophiles: Prefer high temperatures (e.g., hot springs).

• Halophiles: Thrive in high salt concentrations (e.g., salt lakes).

• Acidophiles: Grow in acidic environments.

• Barophiles: Live under high pressure (e.g., deep ocean).

Example: Many archaea are extremophiles, such as Halobacterium (halophile).

Specific Bacteria of Interest

• Mycobacterium: Notable for their waxy cell wall (mycolic acids), making them resistant to desiccation and many antibiotics. Mycobacterium tuberculosis causes tuberculosis.

• Cyanobacteria: Photosynthetic bacteria, important for oxygen production and nitrogen fixation. Sometimes called "blue-green algae."

• Clostridium/Bacillus: Both genera form endospores, allowing survival in harsh conditions. Clostridium botulinum produces botulinum toxin; Bacillus anthracis causes anthrax.

• Alphaproteobacteria (Nitrifying Bacteria): Important in nitrogen cycling; convert ammonia to nitrite and nitrate. Example: Rhizobium forms symbiotic relationships with plants.

Example: Cyanobacteria are unique for their ability to fix atmospheric nitrogen and produce oxygen via photosynthesis.

Eukaryotic Cell Structures & Functions

Mitosis and Meiosis

Mitosis and meiosis are processes of cell division in eukaryotes, differing in their outcomes and roles:

• Mitosis: Division of somatic (body) cells. Produces two genetically identical diploid cells. Ploidy number remains the same.

• Meiosis: Division of gametes (sex cells). Produces four genetically unique haploid cells. Ploidy number halves.

Definitions:

• Haploid (n): One set of chromosomes.

• Diploid (2n): Two sets of chromosomes.

• Ploidy Number: The number of sets of chromosomes in a cell.

Example: Human somatic cells are diploid; gametes are haploid.

Alternation of Generations in Algae

Some algae exhibit alternation of generations, where they alternate between haploid and diploid life stages:

• Sporophyte: Diploid stage that produces haploid spores via meiosis.

• Gametophyte: Haploid stage that produces gametes via mitosis.

Example: Green algae (Ulva) show alternation of generations.

Binary Fission vs Multiple Fission (Schizogony)

• Binary Fission: One cell divides into two.

• Multiple Fission (Schizogony): One cell divides into many daughter cells simultaneously. Common in protozoans like Plasmodium.

Protozoans and Their Morphology

Protozoans are unicellular eukaryotes with diverse morphologies. They are characterized by:

• Motility: Move using flagella, cilia, or pseudopodia.

• Alveolates: A group of protozoans with membrane-bound sacs (alveoli) under their cell membrane. Includes ciliates, dinoflagellates, and apicomplexans.

Example: Paramecium (a ciliate) is an alveolate.

General Difference Between Prokaryotes and Eukaryotes

• Prokaryotes: No nucleus, no membrane-bound organelles, usually smaller.

• Eukaryotes: Have a nucleus and membrane-bound organelles, usually larger.

Viruses, Viroids, & Prions

Key Characteristics of Viruses

Viruses are acellular entities that require a host cell for replication. They are not considered living because:

• They do not carry out metabolism.

• They cannot reproduce independently.

• They lack cellular structure.

Morphology of Viruses

• Capsid: Protein shell surrounding the nucleic acid.

• Nucleic Acid: Can be DNA or RNA, single or double stranded.

• Envelope: Some viruses have a lipid envelope derived from the host cell membrane. Proteins on the envelope determine host specificity.

Viral Genomes

Viruses have diverse genome types:

• +/-ssDNA (single-stranded DNA)

• +/-ssRNA (single-stranded RNA)

• dsDNA (double-stranded DNA)

• dsRNA (double-stranded RNA)

+ssRNA and dsDNA viruses replicate similarly to host cell processes. DNA processing occurs in the nucleus; RNA processing occurs in the cytoplasm of eukaryotic cells.

Viroids and Prions

• Viroid: Infectious RNA molecule without a protein coat; affects plants.

• Prion: Infectious protein; causes neurodegenerative diseases in animals (e.g., mad cow disease).

Lytic vs Lysogenic Cycle

The lytic cycle results in destruction of the host cell, while the lysogenic cycle allows viral genome integration and latency.

• Lytic Cycle Steps (in order):

  1. Attachment

  2. Penetration

  3. Biosynthesis

  4. Maturation

  5. Release

• Lysogenic Cycle: Viral genome integrates into host genome, remains latent until triggered.

Viruses and Cancer

Some viruses can cause cancer by integrating their genome into host DNA, disrupting normal cell regulation (e.g., HPV and cervical cancer).

Virus Culturing in Lab

Viruses are cultured using living cells, such as bacterial lawns (for bacteriophages), animal cell cultures, or embryonated eggs.

Laboratory Techniques

Blood Agar and Hemolysis

Blood agar is used to test for hemolysis, the breakdown of red blood cells by bacterial enzymes. Hemolysis types:

Type	Appearance	Description
Alpha	Greenish	Partial hemolysis
Beta	Clear zone	Complete hemolysis
Gamma	No change	No hemolysis

The streak-stab technique is used to test for anaerobic hemolysis.

Catalase and Oxidase Tests

• Catalase Test: Detects the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen. Positive result: bubbles form when peroxide is added.

• Oxidase Test: Detects cytochrome c oxidase. Positive result: color change on test strip.

pGLO Plasmid Experiment

Plasmids are small, circular DNA molecules in bacteria. The pGLO plasmid contains:

• GFP gene: Encodes green fluorescent protein.

• Arabinose gene: Turns on GFP expression in presence of arabinose.

• Ampicillin resistance gene: Allows growth in presence of ampicillin.

Plate results:

Plate	Plasmid	Growth	Glow
LB	-pGLO	Yes	No
LB/AMP	-pGLO	No	No
LB/AMP	+pGLO	Yes	No
LB/AMP/ARA	+pGLO	Yes	Yes

Arabinose is required to activate GFP expression; ampicillin resistance allows growth in ampicillin.

ELISA

ELISA (Enzyme-Linked Immunosorbent Assay) is used to detect the presence of antigens or antibodies in a sample. The acronym stands for Enzyme-Linked Immunosorbent Assay.

Example: ELISA is commonly used for HIV testing.

Additional info: Academic context was added to clarify definitions, examples, and laboratory procedures for completeness.