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Typical Prokaryotic Cell. Prokaryotic Cell Structures.

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Presentation on theme: "Typical Prokaryotic Cell. Prokaryotic Cell Structures."— Presentation transcript:

1 Typical Prokaryotic Cell

2 Prokaryotic Cell Structures

3 Functions of Cell Membrane  1. Selective barrier (selectively permeable)  2. Secretes exoenzymes  amylases  lipases  peptidases

4 Functions of Cell Membrane  3. E.T.S. is located here  4. Enzymes for cell wall synthesis  5. If photosynthesis, enzymes are located on membranous structures called thylakoids  6. Mesosomes - invagination of cell membrane attached to DNA (Binary Fission)?

5 Cytoplasmic Membrane  Movement across membrane for many substances is controlled by membrane proteins.  Escherichia coli has >200 membrane proteins.  Many of these proteins are involved in transport across membranes.  Others of these proteins allow a bacterium to sense its surrounding environments (e.g., as in chemotaxis).  Movement is via:  Simple Diffusion (including osmosis)  Facilitated Diffusion (with concentration gradient & no energy expended)  Active Transport (against concentration gradient & energy expended)

6 Simple Diffusion - Osmosis

7 Cytoplasmic Membrane

8 Protein-Mediated Transport

9 Active Transport

10 The Prokaryotic Cell Wall Determines cell shape. Prevents osmotic lysis. In some cases recognized by host immune system. Target for antibiotics. Part of cell envelope. In Bacteria, composed of Peptidoglycan.

11 Cell Wall  Main structural component - Peptidoglycan  Peptidoglycan  repeating dissacharide units  polypeptides

12 Gram-Pos vs. Gram-Neg

13 Budowa mureiny


15 Gram-Positive Cell Envelope


17 Gram-Negative Cell Envelope cell wall endotoxin

18 Gram-Negative Cell Envelope Periplasm: Site of preliminary nutrient degradation. LPS: Protection from antibiotics such as penicillin plus against certain toxins.

19 Lipopolysaccharide (LPS) Lipid A = Endotoxin Carbohydrate has negative charge and provides protection against some antibiotics & some toxins (e.g., detergents).


21 Mycoplasma lack Cell Walls Note: Pleomorphic Mycoplasma pneumoniae causes “Walking Pneumonia”

22 Prokaryotic Cell Structure  Glycocalyx - term to describe substances that surround bacterial cells  1. Capsule  if substance is organized and firmly attached to cell wall  2. Slime Layer  if substance is unorganized and loosely attached to cell wall

23 Function of Capsule 1. Contribute to Virulence of bacteria by preventing phagocytosis by WBC’s A. Streptococcus pneumoniae B. Bacillus anthracis

24 Functions of Capsules  2. Prevents drying out or dessication  3. Allows bacteria to adhere to various surfaces  Streptococcus mutans - enamel on teeth to cause dental carries  Klebseilla pneumoniae - attaches to respiratory tract

25 Glycocalyx Protection (e.g., Streptococcus pneumoniae from phagocytosis) Attachment (e.g., Streptococcus mutans causing dental plaques)

26 Capsule Staining Capsules are more regular and gelatinous. Slime Layers are less regular and more diffuse.

27 Flagellar Arrangements also “atrichous” e.g., E. coli Polar Flagellum

28 Chemotaxis Also Phototaxis, etc.

29 Fimbriae (a kind of pilli) Tips are Adhesins, used to adhere, e.g., to animal tissues

30 Motility  Almost all Spiral bacteria are motile  About 1/2 of Bacilli are motile  Almost all Cocci are non-motile

31 Axial Filament - found only in spirochetes (flexible spirals) Treponema pallidum

32 Fimbriae  Filamentous appendages that are shorter, straighter and more numerous that flagella  found mostly in Gram (-) Bacteria  used for attachment not motility

33 E. coli (pathogenic)

34 Nuclear area (nucleoid)  1 circular chromosome (ccDNA)  attached to a mesosome  segragation of DNA during Binary Fission

35 Plasmids  Small circular, extra-chromosomal pieces of DNA  5 to 100 genes  Code for auxiliary metabolic functions:  antibiotic resistance  penicillase  production of toxins  E. coli 0157:H7

36 Ribosomes - protein synthesis  Prokaryotic Ribosome  70 S  50 S  30 S  Eukaryotic Ribosomes  80 S  60 S  40 S

37 Selective Toxicity  Some antibiotics are aimed at the 70 S ribosomes of bacterial cells  Streptomycin, Neomycin, Erythromycin and Tetracycline work by inhibiting protein synthesis by disrupting the 70 S ribosome

38 Endospores - formed under periods of environmental stress  Only found in Gram (+) Bacteria  Bacillus  Bacillus cereus  Bacillus anthracis  Clostridium  Clostridium tetani  Clostridium botulinum  Clostridium perfringens

39 Endospores  Extremely resistant to heat, cold, chemicals, lack of water, etc.  Most vegetative bacterial cells are killed at temps. above 70 C (160 F)  Endospores can survive boiling water for several hours (some for as long as 20 hours)

40 Endospores  Spores can remain viable for weeks, months, years  Thermoactinomyces vulgaris  spores found in Minnesota were 7,500 years old and still germinated

41 Endospores Form inside of vegetative cells (hence “endo”). Highly resistant to heat, U.V., desiccation, etc. Characteristic of many soil bacteria, e.g., Bacillus spp. & Clostridium spp.

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