Microbial Diversity: Prokaryotes, Eukaryotes, and Viruses

Study Guide - Smart Notes

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Binary Fission: The most common method of asexual reproduction in prokaryotes. The cell duplicates its DNA, elongates, and divides into two genetically identical daughter cells.
Budding: A process where a new organism develops from an outgrowth or bud due to cell division at one particular site. The bud detaches to form a new organism.

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 are more similar to eukaryotes than bacteria.
Habitat: Many archaea are extremophiles, while bacteria are found in diverse environments.

Definition: Microorganisms that thrive in extreme environmental conditions (e.g., high temperature, salinity, acidity, or pressure).
Types:
- 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).

Mycobacterium: Known for their waxy cell walls containing mycolic acid, making them resistant to desiccation and antibiotics. Includes pathogens like M. tuberculosis.
Cyanobacteria: Photosynthetic bacteria that produce oxygen; important for Earth's early atmosphere and as primary producers in aquatic environments.
Clostridium and Bacillus: Both genera form endospores, allowing survival in harsh conditions. Clostridium includes obligate anaerobes (e.g., C. botulinum), while Bacillus includes aerobes (e.g., B. anthracis).
Alphaproteobacteria (Nitrifying Bacteria): Important in the nitrogen cycle; convert ammonia to nitrite or nitrate, supporting plant growth.

Be prepared to describe one prokaryote, its group, and unique features (e.g., Mycobacterium for its acid-fast cell wall).

Haploid (n): Cells with one set of chromosomes (e.g., gametes).
Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells).
Ploidy Number: The number of sets of chromosomes in a cell.
Mitosis: Cell division producing two genetically identical diploid cells; used for growth and repair (asexual/somatic).
Meiosis: Cell division producing four genetically unique haploid cells; used for sexual reproduction (gametes). Ploidy number halves.

Algae may alternate between haploid (gametophyte) and diploid (sporophyte) stages, each capable of independent existence.

Binary Fission: One cell divides into two.
Multiple Fission (Schizogony): The nucleus divides several times before the cell splits into many daughter cells (common in some protozoa).

Be prepared to describe one eukaryote, its group, and unique features (e.g., Plasmodium for its complex life cycle).

Definition: Unicellular, eukaryotic organisms, often motile and lacking cell walls.
Alveolates: A group of protozoans with membrane-bound sacs (alveoli) beneath the cell membrane; includes ciliates, dinoflagellates, and apicomplexans.

Feature	Prokaryotes	Eukaryotes
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Cell Wall	Usually present (peptidoglycan in bacteria)	Varies (cellulose in plants, chitin in fungi)
Size	Small (1-10 μm)	Larger (10-100 μm)

Non-living: Viruses are not considered living because they lack cellular structure, metabolism, and cannot reproduce independently.
Obligate Intracellular Parasites: Require host cells to replicate.

Capsid: Protein shell enclosing the viral genome.
Nucleic Acid: Can be DNA or RNA, single- or double-stranded.
Envelope: Some viruses have a lipid membrane derived from the host cell; contains viral proteins for host specificity.

The envelope is acquired from the host cell's plasma membrane or internal membranes during viral budding.

Viruses may have +ssDNA, -ssDNA, +ssRNA, -ssRNA, dsDNA, or dsRNA genomes.
+ssRNA and dsDNA viruses: Their replication is most similar to host cell processes.
Genome Processing: In eukaryotic cells, DNA viruses typically replicate in the nucleus; RNA viruses often replicate in the cytoplasm.

Viroid: Infectious RNA molecules lacking a protein coat; cause diseases in plants.
Prion: Infectious proteins that cause neurodegenerative diseases by inducing abnormal folding of normal proteins (e.g., Creutzfeldt-Jakob disease).

Step	Lytic Cycle	Lysogenic Cycle
1	Attachment	Attachment
2	Entry	Entry
3	Destruction of host DNA	Integration of viral genome into host DNA (prophage)
4	Synthesis of viral components	Latent phase (host cell divides with viral DNA)
5	Assembly	Induction (prophage exits host genome)
6	Release (lysis of host cell)	Lytic cycle resumes

Lytic Cycle: Virus replicates and lyses the host cell, releasing new virions.
Lysogenic Cycle: Viral genome integrates into host DNA and can remain dormant before entering the lytic cycle.

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

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