The Microbial World
Jan 19, 2016
The Microbial World
Tree of Life
• Phylogeny based on 16S ribosomal DNA.
• Three domains of living organisms
• Borderline entities– Viruses
– Viroids
– Prions
Characteristics of Living Organisms
• Metabolism
• Growth
• Reproduction
Characteristics of Cells
• Cell membrane separates cell from outside
• DNA as genetic material
• Ribosomes
• Basic structural macromolecules
• Regulate flow of materials in and out
• Reproduce and are the result of reproduction
• Require energy
Types of Cells
• Prokaryotes
• Eukaryotes
Generally eukaryotic cells are morphologically complex and biochemically simple; prokaryotic cells are morphologically simple and biochemically complex
Prokaryotic Cell (Minimal)
• No “true” nucleus
• No internal membrane bound organelles
Prokaryotic Cell (Maximal)
• Inclusions• External
structures for attachment, genetic exchange, and movement
Prokaryotic Cell Wall
• Unique chemical composition
• Protects cell from osmotic lysis
• Two major types– Gram positive– Gram negative
Gram Negative Cell Walls
Gram Positive Cell Walls
Structures Exterior to the Wall
Glycocalyx/Capsule
• Extracellular polymer
• Important in attachment to surfaces - biofilms
• Protects against phagocytosis
Biofilm Formation
Pili
• Short hairlike appendages projecting from the bacterial cell surface
• Composed of protein• Function:
– Attachment
– Transfer of DNA
Flagella
• Long protein (flagellin) appendage
• Motility• Structure and function
like a propeller• Arrangement of flagella
sometimes used in taxonomy/identification of bacteria
Cell Membrane
• Fluid Mosaic Model
• Phospholipid bilayer with embedded proteins
• Regulates transport of substances into and out of the cell
Membrane Transport
• Diffusion
• Passive/Facilitated Transport
• Group Translocation
• Active Transport
Internal Structures
Nucleoid• Bacterial chromosome• Single circular piece of DNA• No associated histones
Plasmids• Extrachromosomal small piece of DNA
• Independent of chromosome
• Code of ancillary functions– Antibiotic resistance– Metal resistance– Catabolic pathways
• Self-replicating
• Used in genetic engineering
Ribosomes• Combinations of protein and RNA
• Essential structures
• Function– Protein synthesis– Expression of genetic information
• Size differs between prokaryotes and eukaryotes
• Prokaryotes: 70S
Inclusions
• Magnetosomes• Poly-hydroxybutyrate• Sulfur granules• Glycogen• Polyphosphate granules