Microbiology: Lytic and Lysogenic Cycles

The Lytic Cycle

• The virus attaches to the host cell and injects its genetic material
• The viral genes are expressed, using host cell enzymes to create viral proteins
• New viral particles are assembled
• The host cell lyses (breaks open), releasing the new viral particles to infect more cells

The Lysogenic Cycle

• The virus injects its genetic material into the host cell
• The viral genes integrate into the host cell’s genome, becoming latent
• The viral genes are copied along with the host cell's DNA during reproduction, and spread through the infected cell's descendants, remaining inactive
• The virus may later enter the lytic cycle, due to certain environmental factors or chemical triggers

Requirements for Life

• Order: Organized structures
• Sensitivity/Response to Stimuli
• Reproduction
• Growth and Development
• Homeostasis (Maintaining a stable internal environment)
• Energy Processing
• Adaption/Evolution

Archaea

• Single celled microorganisms
• Possess unique biochemistry and genetic makeup compared to bacteria and eukaryotes
• Discovered in extreme environments like hot springs and salty lakes but can be found in more common environments
• Not restricted to extreme environments, as they are abundant in oceans, soils, in and on animals

Prokaryotes

• They are single-celled organisms that lack a nucleus or other membrane-bound organelles
• Two domains: Bacteria and Archaea

Energy Metabolism

• Phototrophs: Energy is derived from the sun (Photosynthesis evolved in bacteria)
• Lithotrophs: Energy is derived from inorganic compounds (example: metal ions)
• Organotrophs: Energy is derived from organic compounds (Organic compounds contain carbon)

Carbon Metabolism

• Autotrophs: Use inorganic carbon (CO2)
• Heterotrophs: Use organic carbon sources
• Inorganic means from non-living as opposed to organic which means from living or once living

Reproduction

• Bacteria and Archaea reproduce asexually through binary fission

Binary fission

• The cell grows in size
• The DNA replicates
• The cell divides into two identical daughter cells

Exchange of Genetic Information

• Transformation: Bacteria take up DNA from their environment
• Transduction: DNA is transferred from one bacteriumto another by a virus
• Conjugation: DNA is transferred directly from one bacterium to another through a pilus

Bacterial Classification

• Shapes:
  • Spherical: Cocci
  • Rod-shaped: Bacilli
  • Spiral or corkscrew-shaped: Spirilla
• Configurations:
  • Chains: “strepto-“ (e.g., streptococcus)
  • Clumps: “staphylo-“ (e.g., staphylococcus)
• Gram Stain: Based on the amount of peptidoglycan present in the cell wall.
  • Gram-positive bacteria: They have a thick peptidoglycan layer, stain purple
  • Gram-negative bacteria: They have a thin peptidoglycan layer, stain pink

The Cell Membrane

• All life requires a body, which a cell membrane provides.
• Functions:
  • Encloses the cell
  • Regulates the passage of molecules in and out of the cell
  • Maintains the cell's internal environment
  • Provides a surface for attachment of proteins and other molecules
  • Enables communication between the cell and its environment
• Unlike prokaryotes, eukaryotic cells also possess internal membranes that encase their organelles

Selective Permeability (Semipermeable Membranes)

• Only allows certain molecules or ions to pass through
• Some small molecules can freely pass through the membrane while others require specific transport proteins

Phospholipids

• The primary component of the cell membranes
• A phosphate head and two fatty acid chain tails

Phosphate Head

• Hydrophilic (water loving)
• Polar
• Water soluble

Fatty Acid Tails

• Hydrophobic (water repelling)
• Non-polar
• Water insoluble

Membrane Proteins

• Proteins are also found in the cell membrane.
• Carry out many different functions:
  • Transport of molecules in and out of the cell
  • Cell signaling
  • Enzymatic activity
  • Cell-cell recognition
  • Structural support
• Example: Proteins to transport glucose molecules in or out of the cell

Endosymbiotic Theory: Evidence

• Mitochondria and chloroplasts are the same size as bacteria
• Mitochondria and chloroplasts have their own DNA
• Mitochondria and chloroplasts divide independently of the cell

This quiz covers the essential concepts of the lytic and lysogenic cycles of viral reproduction, as well as the fundamental requirements for life. Dive into the fascinating world of microorganisms, specifically focusing on viruses and archaea. Test your knowledge of these processes and how they relate to the characteristics of living organisms.