Transcript PROKARYOTES
PROKARYOTES THEY ARE EVERYWHERE The Major Similarities Between the Two Types of Cells (Prokaryote and eukaryote) Are: • They both have DNA as their genetic material. • They are both membrane bound. • They both have ribosomes . • They have similar basic metabolism . • They are both amazingly diverse in forms. How Prokaryotes Differ from Eukaryotes • Smaller and lack membrane bound organelles • Have cell walls but composition is different from that of plants and fungi • Have simplier genomes – Differ in genetic replication – Protein synthesis – recombination Prokayotes Have a Tremendous Impact on the Earth • Small percentage cause diseases • Decomposers – Key to life-sustaining chemical cycles • Form symbiotic relationships – Mitochondria and Chlorophast may have evolved from such symbiosis Three Domains Two Kingdoms of Prokaryotes • Archaebacteria – Evolved from the earliest cells – Inhabit extreme environments • Eubacteria – Modern prokaryotes – More numerous Structure • Cocci (spheres) • Bacilli (rods) • Spirilla and spirochetes (helices) Prokaryotic Cell Wall • Major material is PEPTIDOGLYCAN – Modified sugar polymers cross-linked by short polypeptides – Exact composition varies among species – Some antibiotics work by preventing the formation of cross links thus preventing the formation of a functional cell wall Gram Stain – a Stain Used to Distinguish Two Groups of Bacteria • Gram-Positive – Have simple walls with large amounts of peptidoglycan – Stain blue • Gram-Negative – More complex with less amounts of peptidoglycan – Outer lipopolysaccharide containing membrane – Stain pink – Often pathogenic 50% of Bacteria Use One of Three Mechanism to Move 1. Flagella 2. Filaments 3. Gliding • Taxis – movement to or away from a stimulus. Stimuli may be: – Phototaxis – Chemotaxis – magnetotaxis Cellular and Genomic Organization • Infolding of the plasma membrane – cellular respiration in aerobic bacteria • Cyanobacteria have thylakoid membranes • Genome as 1/1000 as much DNA as that of a eukaryote • One double stranded, circular DNA • DNA concentrated in the nucleoid region • Contain plasmids • Ribosomes are smaller and have different proteins and RNA content from eukaryotes – This allows some antibiotics to block bacterial protein production will not adversely affecting the eukaryote proteins Prokaryotes Grow and Adapt Rapidly • • • • • Binary fission Transformation Conjugation Transduction Endospores Prokaryotes May Be Grouped According to How They Obtain Energy • Photoautotrophs – photosynthetic and use light for energy • Chemoautotrophs – need only CO2 as a source of carbon and obtain energy by oxidizing inorganic substances • Photohetrotrophs – use light to make ATP but must obtain carbon in organic form • Chemoheterotrophs- must consume organic material for both energy and carbon