Bacteria
Prokaryotes Single-celled organisms that do not have organelles Commonly referred to as bacteria 3 shapes: Rod shaped (bacillus) Sphere shaped (coccus) Spiral shape (spirillum) Divided into two domains: Domain Archaea Domain Bacteria
Domain Archaea Found in many places, including extreme environments (salt lakes & hot springs) Structurally different from Bacteria Some similar to eukaryotes; others unique among living organisms
Domain Bacteria Most prokaryotes belong to this domain Found everywhere One square inch of skin contains an average of 100,000 bacteria
Bacterial Structure Bacterial DNA is a single chromosome called a nucleoid Extra loops of DNA are called plasmids Have cell walls made of a protein-carbohydrate compound called peptidoglycan Gram-positive bacteria have thick layers of peptidoglycan & no outer membranes Gram-negative bacteria have thin layers of peptidoglycan & outer membranes
Gram-Positive Bacteria Gram stain contains a purple and a pink dye Purple dye is applied first The thick peptidoglycan layer of Gram-positive bacteria will absorb the purple dye, causing it to look purple after its been stained
Gram-Negative Bacteria Does not have a thick layer of peptidoglycan Outer membranes will not trap the purple dye, but will absorb the pink dye, causing it to look pink when stained Outer membranes make them better able to resist host defenses & medicines
Obtaining Energy & Nutrients Bacteria can be placed into 3 groups based on how they get energy & nutrients: Photoautotrophs—get energy from sunlight through photosynthesis Chemoautotrophs—get energy from inorganic sources; can make their own amino acids & proteins in the presence of hydrogen-rich chemicals Heterotrophs—get their energy from other organisms
Reproduction & Adaptation Binary Fission—asexual reproduction used by bacteria to create 2 identical cells from 1 original cell Genetic Recombination—3 ways for bacteria to form new genetic combinations: Conjugation—when 2 bacteria exchange genetic material
Reproduction & Adaptation, cont. Transformation—when bacteria pick up DNA fragments from their environments Transduction—when genetic material (plasmid) is transferred by a virus Plasmids have resistance to antibiotics Endospore Formation—when bacteria form thick-walled structures that surround their DNA & some of their cytoplasm Can survive harsh conditions & lay dormant for hundreds of years before being revived