Prokaryotes

1. Prokaryotes Chapter 23

2. Features of Prokaryotes Cellular organisms In one of two domains: Archaea and Eubacteria Generally smaller than eukaryotes Most are unicellular, some form colonies or filaments No membrane-enclosed organelles Ribosomes are located in the cytoplasm In some – the inner plasma membrane is extensively folded inward to provide reaction sites Most have a cell wall

3. Shapes of Prokayrotes • Cocci– spherical • Single cells • Groups of two: diplococci • Long chains: streptococci • Clumps: staphylococci • Bacilli– rod-shaped • In single rods or long chains • Spiral: • Spirochete – flexible spiral • Spirillum – rigid spiral • Vibrio – spirillum shaped like a comma

4. Bacterial Shapes

5. Cell Wall Provides shape and stability Allows the cell to inhabit hypotonic surroundings without bursting Does not help in hypertonic solutions – most bacteria do not grow well in foods preserved with high sugar or salt content In eubacteria the cell wall contains peptioglycan

6. Gram staining • Gram-positive bacteria: • Appear blue or violet • Cell walls with a very thick layer of peptidoglycan • Disease causing gram-positive bacteria are easily killed by penicillin which interferes with peptidoglycan production • Gram-negative bacteria: • Appear red or pink • Cell walls have two layers: a thin peptidoglycan layer and a thick outer membrane

7. Other bacterial structures • Capsule– a slime layer that surrounds the cell wall in some species • May provide pathogenic bacteria protection • May also allow some bacteria to attach to surfaces (e.g.: to cause dental plaque) • Pili– short, hair-like projections of protein which allow bacteria to adhere to each other or other surfaces • Flagella– longer projections found in mobile bacteria

8. Bacterial structures

9. Prokaryote DNA In cytoplasm, not surrounded by a membrane In most, a singular circular chromosome Most bacteria also contain smaller circular plasmidswhich may contain genes that code for enzymes, genetic exchange, or antibiotic resistance

10. Bacterial DNA

11. Bacterial Reproduction • Asexual: • Binary fission – DNA replication followed by a transverse wall separating the two new cells • Budding– a bulge forms and matures, eventually separating from the original cell • Fragmentation– walls develop within a single cell which then separates into several different cells • Genetic exchange: • Transformation– fragments of DNA released by one cell are picked up by another • Transduction– a phage (form of a virus) carries bacterial DNA from one to another • Conjugation– two different bacterial cells exchange genetic material

12. Bacterial Reproduction

13. Endospore Formation Some bacterial form dormant, extremely durable cells in response to unfavorable environmental conditions Tetanus, gas gangrene, anthrax can all form endospores

14. Prokaryotic Metabolism • Heterotrophs– most bacteria obtain energy from surroundings: • Chemoheterotrophs– decomposers and pathogens • Photoheterotrophs– get carbon from other organisms but have chlorophyll to trap sunlight energy • Autotrophs– manufacture their own organic molecules • Photoautotrophs– use photosynthesis • Chemoautotrophs– use chemosynthesis

15. Prokaryote Classification • Archaea: • No peptidoglycan in cell walls • Many live in extremely harsh environments: no oxygen, high salt, or high temperatures • Eubacteria: • Peptidoglycan in cell walls • Widely distributed and better known

16. Ecological Significance • Decomposers • Recycle chemical nutrients necessary for life • Especially important in the nitrogen cycle • Pathogens • Exotoxins- poisons produced by the bacteria that cause the damage • Endotoxins– components of the cell walls that affect the host only when released from the dead bacteria • Food production • Microbial fermentation – yogurt, pickles, olives, sauerkraut, vinegar, soy sauce • Antibiotic production • Genetic engineering • Bioremediation