Porkaryotic Cell Structure and Function

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Processes of Life. GrowthReproductionResponsivenessMetabolism. Prokaryotic Cells. Comparing Prokaryotic and Eukaryotic CellsProkaryote comes from the Greek words for prenucleus.Eukaryote comes from the Greek words for true nucleus.. ProkaryoteOne circular chromosome, not in a membraneNo histo

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Porkaryotic Cell Structure and Function

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1. Chapter 4 Porkaryotic Cell Structure and Function

2. Processes of Life Growth Reproduction Responsiveness Metabolism

3. Prokaryotic Cells Comparing Prokaryotic and Eukaryotic Cells Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for true nucleus.

4. Comparing Prokaryotes and Eukaryotes

5. Comparing Prokaryotes and Eukaryotes

6. Average size: 0.2 -1.0 µm ? 2 - 8 µm .5 µm 2 µm Basic shapes: Cocci – round Bacilli – rod Spiral

7. Arrangements

8. Arrangements

9. Arrangements

10. External Structures of Prokaryotic Cells Glycocalyces Flagella Fimbriae and pili

11. Glycocalyces Gelatinous, sticky substance surrounding the outside of the cell Composed of polysaccharides, polypeptides, or both Two types Capsule Slime layer

12. Capsule Composed of organized repeating units of organic chemicals Firmly attached to cell surface Protects cells from drying out May prevent bacteria from being recognized and destroyed by host

13. Slime Layer Loosely attached to cell surface Water soluble Protects cells from drying out Sticky layer that allows prokaryotes to attach to surfaces

14. Flagella Are responsible for movement Have long structures that extend beyond cell surface Not all prokaryotes have flagella Filament capable of rotating 360ş

15. Arrangements of Bacterial Flagella Peritrichous: distributed throughout the surface of the bacterium

16. Arrangements of Bacterial Flagella Monotrichous: a single flagella at one end.

17. Arrangements of Bacterial Flagella Lophotrichous: many flagella located at one end of the bacterium.

18. Function of Bacterial Flagella Rotation propels bacterium through environment Rotation can be clockwise or counterclockwise; reversible Bacteria move in response to stimuli (taxis) Runs – movements of cell in single direction for some time due to counterclockwise flagellar rotation; increase with favorable stimuli (positive chemotaxis, positive phototaxis) Tumbles – abrupt, random, changes in direction due to clockwise flagellar rotation; increase with unfavorable stimuli (negative chemotaxis, negative phototaxis)

19. Function of Bacterial Flagella

20. Fimbriae and Pili Nonmotile extensions Fimbriae Sticky, proteinaceous, bristlelike projections Used by bacteria to adhere to one another, to hosts, and to substances in environment May be hundreds per cell and are shorter than flagella Serve an important function in biofilms

21. Pili Long hollow tubules Longer than fimbriae but shorter than flagella Bacteria typically only have one or two per cell Join two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation)

22. Prokaryotic Cell Wall Provides structure and shape and protects cell from osmotic forces (cell bursting from excess water uptake). Assists some cells in attaching to other cells or in eluding antimicrobial drugs Animal cells do not have; can target cell wall of bacteria with antibiotics

23. Bacterial Cell Wall Most have cell wall composed of peptidoglycan; a few lack a cell wall entirely. Peptidoglycan composed of sugars, NAG, and NAM Chains of NAG and NAM attached to other chains by tetrapeptide crossbridges Bridges may be covalently bonded to one another Bridges may be held together by short connecting chains of amino acids

24. Peptidoglycan Polymer of disaccharide N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)

25. Peptidoglycan NAG and NAM are linked by polypeptides

26. Gram-Positive Cell Wall Relatively thick layer of peptidoglycan Contains unique polyalcohols called teichoic acids Some covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane Polysaccharides provide antigenic variation Acid-fast bacteria contain up to 60% mycolic acid helps cells survive desiccation (drying out). Example: Mycobacterium tuberculosis – causative agent of TB

27. Gram-positive Cell Wall

28. Gram-Negative Cell Walls Have only a thin layer of peptidoglycan. Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

29. Union of lipid with sugar Also known as endotoxin Lipid portion known as lipid A Dead cells release lipid A when cell wall disintegrates May trigger fever, vasodilation, inflammation, shock, and blood clotting Can be released when antimicrobial drugs kill bacteria LPS

30. Periplasmic Space Located between outer membrane and cell membrane Contains peptidoglycan and periplasm Contains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport

31. Prokaryotic Cytoplasmic Membrane Referred to as phospholipid bilayer; composed of lipids and associated proteins Approximately half the membrane is composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channels Integral proteins Peripheral proteins Glycoproteins

32. Phospholipid Bilayer of Cytoplasmic Membrane

33. Cytoplasmic Membrane Function Controls passage of substances into and out of the cell; selectively permeable Functions in energy storage Harvests light energy in photosynthetic prokaryotes

34. Control of Substances Across Cytoplasmic Membrane Naturally impermeable to most substances Proteins allow substances to cross membrane Occurs by passive or active processes Maintains a concentration gradient and electrical gradient Chemicals concentrated on one side of the membrane or the other Voltage exists across the membrane

35. Passive Processes of Transport Diffusion: movement of small, non-polar molecules into and out of the cell. Facilitated diffusion: movement of ions or polar molecules into and out of the cell with the aid of a transport protein. Osmosis: movement of water into and out of the cell based on the solutes present in the surrounding solution. Isotonic solution Hypertonic solution Hypotonic solution

36. Effects of Solutions on Organisms

37. Overview of Passive Transport

38. Active Processes of Transport Active Transport Utilizes permease proteins and expends energy (typically in the form of ATP)

39. Cytoplasm of Prokaryotes Cytosol – liquid portion of cytoplasm Inclusions – may include reserve deposits of chemicals Ribosomes – sites of protein synthesis Cytoskeleton – plays a role in forming the cell’s basic shape Some bacterial cells produce dormant form called endospore. Protective structure that allows some bacteria to survive adverse conditions.

40. Endospores Tough, outer coat protects from extreme conditions; Dormant, non-reproductive form of bacteria. Very few bacteria can form endospores.

41. Chapter 4: Case Study #1 - Massive Tissue Death in a Diabetic Patient   On 23 November 1997, a 52-year old male diabetic entered the hospital with massive necrosis of the tissue of the foot (Figure 1), as well a large bubble within the tissue. A patient background demonstrated a history of high blood sugar due to poor diet and lack of insulin administration. This resulted in arteriosclerosis (blockage of blood vessels) within the patient. Bacteria were cultured from the foot. Bacteria grew only under anaerobic conditions and produced endospores. A gram stain revealed the presence of a gram positive cell wall.   Questions: 1. Describe a gram positive cell wall.   2. Describe the structure and function of an endospore.   3. Is an endospore a reproductive structure? Explain.

42. Chapter 4: Case Study #2 – No chips and dip for me, thanks…. A multi-state outbreak of bloody diarrhea with at least 30 culture-confirmed cases in California, Oregon, and Washington was linked to eating a nationally distributed five-layer dip. The onset of symptoms occurred between 10 and 23 January 2000. The implicated product was manufactured by Senor Felix’s Mexican Foods (Baldwin Par, CA). The dip consisted of layers of beans, salsa, guacamole, nacho cheese, and sour cream. The dip was made without the addition of food preservatives. The cause of this outbreak was revealed to be Enterohemorrhagic E. coli (E. coli O157:H7). This is a gram-negative organism causes bloody diarrhea and no fever. EHEC can cause hemolytic-uremic syndrome and sudden kidney failure. It uses bacterial fimbriae, is moderately-invasive and possesses a phage-encoded Shiga toxin that can elicit an intense inflammatory response (Wiki). It also possesses an endotoxin that illicit further inflammation of the colon. The flagella of E. coli have a peritrichous arrangement. E. coli and related bacteria possess the ability to transfer DNA, which allows genetic material to spread horizontally through an existing population. Questions: 1. Describe the structure of a gram negative cell wall in detail. 2. What is an endotoxin and where is it found? Do both gram negative and gram positive organisms produce endotoxins? Explain. 3. What is the function of fimbriae? 4. What is the function of a flagella? Describe a peritrichous arrangement. 5. What structure allows a bacterium to transfer DNA from one cell to another?

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