CH 19 - Chapter 19 The Diversity of Prokaryotes and Viruses...

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Chapter 19 The Diversity of Prokaryotes and Viruses
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19.1 Which Organisms Are Members of the Domains Archaea and Bacteria? Earth’s first organisms were prokaryotes, single- celled microbes that lacked organelles Prokaryotes are still abundant, forming two of life’s three domains 1. Bacteria 2. Archaea
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Bacteria and Archaea are fundamentally different Similarities between Bacteria and Archaea They are both prokaryotic They are both single-celled organisms Differences between Bacteria and Archaea Bacteria have peptidoglycan in their cell walls; Archaea don’t There are also differences in the plasma membrane composition, ribosomes, and RNA polymerases between the two domains Differences in transcription and translation also exist between the two
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Classification of prokaryotes within each domain is difficult Prokaryotes are very and structurally simple Prokaryotes do not have many anatomical differences that can be used to differentiate them Features used in prokaryotic classification are: 1. shape 2. means of locomotion 3. pigments 4. nutrient requirements 5. colony appearance 6. gram staining characteristics 7. nucleotide sequences
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Prokaryotes differ in shape and structure Both bacteria and archaea are very small, ranging from 0.2 to 10 micrometers in diameter Prokaryotes have three common shapes 1. Spherical (cocci) 2. Rod-like (bacilli) 3. Corkscrew-shaped (spirilli) Fig. 19-1
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Spherical (cocci) Spherical (cocci) Rod-shaped (bacilli) Corkscrew-shaped (spirilli)
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19.2 How Do Prokaryotes Survive and Reproduce? Some prokaryotes are motile – Flagella are the primary means of locomotion –found singly, in pairs, as a tuft at one end of the cell, or scattered over the entire cell surface –In bacteria, a “wheel-and-axle” arrangement anchors the flagellum within the cell wall and plasma membrane, enabling the flagellum to rotate rapidly Fig. 19-2
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Many bacteria form films on surfaces Some bacteria secrete sticky layers of polysaccharide or protein slime Communities of slime-secreting bacteria are called biofilms ; dental plaque is a biofilm Bacteria embedded in biofilms are protected from disinfectants and antibiotics Can cause tooth decay Fig. 19-3
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Protective endospores allow some bacteria to withstand adverse conditions Endospores form inside some bacteria under extreme environmental conditions – Endospores are thickly-wrapped particles of genetic material and a few enzymes – Endospores are resistant to extremes –Survival in boiling water –Stable and long-live (>250 million years) –Ideal bio-terror agent (e.g. anthrax spores) – When a hospitable environment is found, metabolism resumes and the endospore develops into a fully functioning bacterium
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Spores Protect Some Bacteria Fig. 19-4
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Prokaryotes are specialized for specific habits – Each species is specialized for certain environmental conditions and usually cannot survive outside a narrow range around those conditions
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