Microbiology Study Guide: Prokaryotes, Eukaryotes, and Viruses (Chapters 11–13)

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Prokaryotes reproduce asexually, meaning offspring are genetically identical to the parent. The main methods include:

Binary Fission: The most common method. The cell duplicates its DNA, elongates, and divides into two identical daughter cells.
Budding: A small outgrowth (bud) forms on the parent cell, enlarges, and eventually detaches to become a new cell.

Example: Caulobacter species reproduce by budding, while most bacteria use binary fission.

Cell Wall Composition: Bacteria often have peptidoglycan in their cell walls; archaea do not.
Membrane Lipids: Archaea have ether-linked lipids; bacteria have ester-linked lipids.
Genetic Machinery: Archaeal transcription and translation are more similar to eukaryotes than to bacteria.
Habitat: Archaea are often extremophiles, while bacteria are found in diverse environments.

Extremophiles are organisms that thrive in extreme environments. These include:

Most extremophiles are archaea.

Mycobacterium: Has a waxy cell wall (mycolic acids), making it resistant to desiccation and antibiotics. Includes pathogens like M. tuberculosis.
Cyanobacteria: Photosynthetic bacteria that produce oxygen; important for Earth's early atmosphere.
Clostridium and Bacillus: Both genera form endospores, allowing survival in harsh conditions. Clostridium includes pathogens like C. botulinum.
Alphaproteobacteria (Nitrifying Bacteria): Convert ammonia to nitrite and nitrate, playing a key role in the nitrogen cycle.

Example: Bacillus anthracis causes anthrax and forms highly resistant endospores.

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 chromosome sets in a cell.
Mitosis: Produces two genetically identical diploid cells; used for growth and repair (asexual/somatic).
Meiosis: Produces four genetically unique haploid cells; used for sexual reproduction (gametes).

Ploidy Changes: Mitosis maintains ploidy; meiosis halves it.

Many algae alternate between haploid (gametophyte) and diploid (sporophyte) generations, a process called alternation of generations.

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 (e.g., Plasmodium).

Protozoans: 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.

Example: Paramecium (a ciliate) is an alveolate protozoan.

Prokaryotes: No nucleus, usually single circular chromosome, no membrane-bound organelles.
Eukaryotes: True nucleus, multiple linear chromosomes, membrane-bound organelles (e.g., mitochondria, ER).

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

Can be +ssRNA, -ssRNA, dsDNA, dsRNA, or ssDNA.
+ssRNA and dsDNA viruses have genome types most similar to host cell genetic material.
DNA viruses typically replicate in the nucleus; RNA viruses often replicate in the cytoplasm.

Viroid: Infectious RNA molecule lacking a protein coat; causes plant diseases.
Prion: Infectious protein that causes neurodegenerative diseases by inducing misfolding of normal proteins (e.g., Creutzfeldt-Jakob disease).

Step	Lytic Cycle	Lysogenic Cycle
1	Attachment	Attachment
2	Entry	Entry
3	Destruction of host DNA	Viral genome integrates into host DNA (prophage)
4	Synthesis of viral components	Prophage is replicated with host DNA
5	Assembly of virions	Can enter lytic cycle later
6	Release (lysis of host cell)	Host cell survives until induction

Lytic Cycle: Virus replicates and destroys host cell. Lysogenic Cycle: Viral genome integrates into host genome and can remain latent.

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

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