Microbiology Study Notes lab partner notes

Viral Replication

Lytic Cycle

The lytic cycle is a process by which bacteriophages (viruses that infect bacteria) replicate and ultimately destroy their host cell. This cycle is characterized by the rapid production of new viral particles and the lysis (breaking open) of the host cell.

• Attachment: The virus attaches to specific structures on the external surface of the host cell. This specificity is often determined by the phage's recognition of unique receptors.

• Entry: The viral genome enters the host cell, often facilitated by the breakdown of the peptidoglycan layer in bacteria, releasing lysosomal enzymes.

• Synthesis: The host cell's machinery is hijacked to synthesize viral components, replacing the host DNA with viral DNA.

• Assembly: Newly synthesized viral components are assembled into complete virions.

• Release: The host cell is lysed, releasing new virions to infect other cells.

Example: T4 bacteriophage infecting Escherichia coli.

Lysogenic Cycle

The lysogenic cycle involves the integration of the viral genome into the host cell's chromosome, where it can remain dormant for extended periods. The virus does not immediately destroy the host cell but can later enter the lytic cycle.

• Attachment: Virus attaches to the host cell.

• Entry: Viral genome enters the cell.

• Prophage Formation: Viral DNA integrates into the host chromosome, becoming a prophage.

• Replication: As the host cell replicates, the viral genome is also replicated.

• Induction: Environmental triggers can activate the prophage, causing it to exit the chromosome.

• Synthesis, Assembly, Release: The virus resumes the lytic cycle, producing new virions and lysing the cell.

Example: Lambda phage in Escherichia coli.

Endocytosis

Endocytosis is a process by which eukaryotic cells internalize substances, including viruses, by engulfing them in a membrane-bound vesicle. This is a common entry mechanism for animal viruses.

Microbial Morphology and Culture

Morphology

Morphology refers to the shape and structural characteristics of microorganisms. Common shapes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

Cultural Characteristics

Cultural characteristics describe how microorganisms grow in laboratory media, including colony shape, color, and texture.

Microbial Diversity and Cell Structure

Archaea

Archaea are extremophilic prokaryotes, often found in harsh environments such as hot springs, salt lakes, and deep-sea vents.

Bacterial Cytoplasmic Membrane

The bacterial cytoplasmic membrane does not provide shape to the cell; shape is determined by the cell wall, particularly the peptidoglycan layer.

Retroviridae

Retroviridae are viruses that use the enzyme reverse transcriptase to replicate their genome. This enzyme synthesizes DNA from an RNA template, a process seen in viruses like HIV.

• Example: HIV uses reverse transcriptase to convert its RNA genome into DNA, which integrates into the host genome.

$\text{RNA} \xrightarrow{\text{Reverse Transcriptase}} \text{DNA}$

Phage and Virons

Phage refers to a bacteriophage, a virus that infects bacteria. A phage genome is a small chromosomal piece. Virons are complete viral particles with the same genetic information, coding for similar functions.

Viral Enzymes

Viruses do not use their own enzymes for replication; they rely on the host cell's machinery.

Measurement

Bacteria and viruses are measured in nanometers. Viruses are generally smaller than bacteria.

Prions

Prions are infectious proteins that cause neurodegenerative diseases, such as Creutzfeldt-Jakob disease.

Glycocalyx

The glycocalyx is a sticky layer on the surface of bacterial cells, aiding in attachment and protection.

Algae

Algae are photosynthetic organisms that thrive in wet, moist environments.

Inclusion Bodies

Inclusion bodies are storage sites within cells for nutrients, waste, or other substances.

Endospores

Endospores are dormant, tough, and non-reproductive structures produced by some bacteria to survive environmental changes.

Microbial Relationships and Significance

Symbiotic Relationships

A symbiotic relationship is when organisms live together and benefit from each other. Examples include mutualism, commensalism, and parasitism.

Koch's Postulates

The major significance of Koch's postulates is the demonstration that microorganisms cause disease. These postulates are foundational in medical microbiology.

Biogenesis

Biogenesis is the principle that living organisms arise from pre-existing life, not from non-living matter.

Prokaryotic Ribosomes

Prokaryotic ribosomes are 70S, composed of 30S and 50S subunits.

$\text{70S} = \text{30S} + \text{50S}$

Summary Table: Key Microbial Terms

Term	Definition	Example/Application
Lytic Cycle	Viral replication that destroys host cell	T4 phage in E. coli
Lysogenic Cycle	Viral genome integrates into host chromosome	Lambda phage in E. coli
Archaea	Extremophilic prokaryotes	Thermophiles in hot springs
Retroviridae	Viruses with reverse transcriptase	HIV
Prion	Infectious protein	Creutzfeldt-Jakob disease
Glycocalyx	Attachment layer on bacteria	Streptococcus mutans
Endospore	Dormant survival structure	Bacillus anthracis

Additional info:

• Some points were expanded for academic clarity and completeness.

• Examples and definitions were added to make the notes self-contained.