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BLG 151 - Chapter 3 - Cell Structure and Function.docx

BLG 151 - Chapter 3 - Cell Structure and Function.docx -...

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Chapter 3 Cell Structure and Function 3.0 Bacterial Shapes, Arrangements and Sizes Shape: Arrangements: Name of Cocci Arrangements Name of Bacilli/ Spirochete Arrangements (Rigid helices) (Flexible helices) Two other shapes of bacteria are mycelium and pleomorphic: o mycelium – network of long, multinucleate filaments o pleomorphic – organisms that are variable in shape The size of bacteria varies from 0.3 μm to 600 x 80 μm. Why are bacteria so small? Bacteria are so small in size because their small size is necessary for sufficient nutrient uptake and protective mechanisms from predation. o Bacteria have limited organelles, so if they were to grow bigger, there would be empty space and this empty space would take up energy and lower the efficiency of their system 3.1 Bacterial Structure Inclusions – storage of carbon, phosphate, and other substances Gas vacuole – an inclusion that provides buoyancy for floating in aquatic environments Periplasmic space – In typical Gram-negative bacteria: contains hydrolytic enzymes and binding proteins for nutrient processing and uptake; in typical Gram-positive bacteria, may be smaller or absent Capsules and slime layers – resistance to phagocytosis, adherence to surfaces Fimbriae and pili – attachment to surfaces, bacterial conjugation and transformation, twitching and gliding motility Flagella – swimming and swarming motility
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Endospore – allows survival under harsh environmental conditions NOTE: not all bacterial cells have flagella and/or fimbriae 3.2 How We Study Cell Parts: Cell Envelope – Exploring the Cell Wall A cell wall is a rigid structure that lies just outside the cell plasma membrane and is composed of peptidoglycan (Murein) o The peptidoglycan structure consists of 2 alternating sugars: N -acetylglucosamine (NAG) and N - acetylmuramic acid (NAM) Cells that lose their cell wall can survive in isotonic environments – an environment having the same osmotic pressure as the plasma membrane (note: the plasma membrane evolves its osmotic pressure resistance) Cell walls differentiate two types of bacteria: 1. Gram-positive: stain purple; think peptidoglycan Composed of mainly peptidoglycan, but also contains teichoic acids , which are negatively charged. Teichoic acids help: Maintain the cell envelope Protect the cell envelope from environmental substances Bind to host cells Some gram-positive bacteria also have a layer of proteins on the surface of peptidoglycan: S-layer and capsule Gram-positive bacteria also have smaller periplasmic space (space between plasma membrane and cell wall) than gram-negative bacteria 2. Gram-negative: stain pink or red; thin peptidoglycan and outer membrane More complex than Gram-positive Does not have teichoic acids Consist of a thin layer of peptidoglycan enclosed by an inner and outer membrane, whereby the outer membrane is composed of lipids, lipoproteins,
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