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Lecture 2: Functional Anatomy of Prokaryotic and Eukaryotic cells Edith Porter, M.D. 1.

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Presentation on theme: "Lecture 2: Functional Anatomy of Prokaryotic and Eukaryotic cells Edith Porter, M.D. 1."— Presentation transcript:

1 Lecture 2: Functional Anatomy of Prokaryotic and Eukaryotic cells Edith Porter, M.D. 1

2  Major characteristics of prokaryotic and eukaryotic cells  Prokaryotic cells  Size, shape arrangement  Structures external to cell wall  Cell wall  Structures internal to cell wall  Eukaryotic cells  Flagella and cilia  Cell wall and glycokalyx  Plasma membrane  Ribosomes and organelles  Evolution of eukaryotes 2

3 3  One circular chromosome, not in a membrane  No histones  No organelles  Peptidoglycan cell walls if Bacteria  Pseudomurein cell walls if Archaea  Binary fission  Paired chromosomes, in nuclear membrane  Histones  Organelles  Polysaccharide cell walls  Mitotic spindle

4  Typically fixed shape due to cell wall  Peptidoglycan (murein) in bacteria  Pseudomurein in archaea  Rod: bacillus (E.coli)  Coccus: round, spherical  Diplococci (N. meningitidis)  Streptococci (S. pyogenes)  Tetrades (Micrococci)  Sarcinae  Staphylococci (Staphylococcus epidermidis)  Spiral  Fixed: spirilla  Flexible: spirochetes (Treponema pallidum) 4

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8  Unusual  Star-shaped  Squares  Triangular  Pleomorphic  Within a population various shapes (Corynebacteria)  No fixed shape  Cellwall-less: Mycoplasma/Ureaplasma Shape is influenced by environmental conditions, age of culture, antibiotic pretreatment! 8

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10 10  Outer most layer  Outside cell wall  Usually sticky  Composed of mostly of carbohydrates, sometimes of protein  Capsule: neatly organized  Slime layer: unorganized and loose  Biofilm or extracellular polymeric substance (EPS)  Extracellular polysaccharide allows cell to attach  Capsules prevent phagocytosis

11  Generate movement  Protein structure  H-antigen (“Hauch”, used for typing)  Consists of 3 parts:  Filament: flagellin subunits (H-antigen), helical arranged  Hook  Basal body: anchors into the cell wall via rings, here movement is generated 11

12 12 In Gram-negative bacteriaIn Gram-positive bacteria

13  Peritrichous: Many around 13  Monotrichous : One only  Lophotrichous: Multiple at one end  Amphitrichous : At both ends

14 14  Also called endoflagella  In spirochetes (e.g., Treponema, Borrelia)  Anchored at one end of a cell and beneath an outer sheet  Rotation causes cell to move  Suited for movement in viscous surrounding

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16  Chemotaxis  Directed movement  In response to a chemical  Through a specific chemoreceptor on the cell  Movement to a chemical: chemical is a chemoattractant (e.g. sugar, amino acid)  Movement away from chemical: chemical is a chemorepellent (toxic substance) 16

17  Cell appendages in mostly gram-negative bacteria  Made out of protein subunits (pilin)  Thinner than flagella  Fimbria  a few – hundreds  Main function is attachment  Pili  typically 1 or 2 only and longer  DNA transfer: Specialized sex pili transfer plasmids during bacterial conjugation  Twitching motility and gliding motility 17

18 Figure

19  Peptidoglycan is major component  Cross linkage of peptides + sugars  Sugars: multiple layers of alternating N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG)  Peptides: tetrapeptide crosslink between NAM from different layers, D- and L- amino acids NAG NAM NAGNAM 19

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21  Gram-positive  Many layers of peptidoglycan  Additional components ▪ Teichoic acid, lipoteichoic acids  Periplasm in the space between cell membrane and peptidoglycan  Gram-negative  One or few layers of peptidoglycan  Additional outer membrane ▪ Mainly composed of lipopolysaccharide  Lipoproteins connect peptidoglycan with outer membrane  Periplasm between cell membrane and peptidoglycan and between peptidoglycan and outer membrane 21

22  Lipid A  the culprit for fever (endotoxin)  highly conserved  Core sugar  conserved  Sugar chain of varying length (O-antigen, “ohne Hauch”, used for typing) Lipid A Core 22

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25  Gram stain:  1 min Crystal violet  1 min Iodine  destain in alcohol  1 min safranin  2 types of staining: gram+ gram-  Gram+: thick PG  Gram-: thin PG, om 25

26 Table 4.1 None

27 ACID FAST CELL WALLS  Rich in mycolic acids  E.g. Mycobacterium spec  Hard to penetrate  Require heat for staining ARCHAEA  No peptidoglycan (murein)  Pseudomurein 27

28  Penicillin: inhibits transpeptidases  Lysozyme: breaks glycosidic bond between NAM and NAG  Autolysins: self destruction of peptidoglycan, important for cell divisions NAG NAM NAGNAM Penicillin Lysozyme 28

29  Also called inner membrane  Double phospholipid layer with proteins (often glycoproteins)  Lipids differ from eukaryotic cell membranes  No sterols (exception: Mycoplasma steal sterols from host)  Protection towards outside  Containment of cytoplasmic material  Selective uptake of molecules  Site of energy production in many species  Target of some antibiotics (e.g. polymyxin B) and disinfectants (e.g. alcohols) 29

30 Figure

31  ~80% water  Contains primarily proteins (enzymes), carbohydrates, lipids, inorgainc ions, many low molecular weight compounds  Thick, aqueous, semitransparent, and elastic 31 (from Slonczewski 2009)

32  Bacterial chromosome  Contains the essential genetic information  Circular double-stranded DNA Stabilized by histone-like proteins (not by histones)  No nuclear envelope!! 32

33  Small circular double-stranded DNA that can multiply independently  Not essential under normal physiological conditions  Contain additional genes often involved in pathogenesis  virulence factors  antibiotic resistance  toxic metal resistance  Copy number varies (a few – hundreds)  Can be exploited for recombinant protein production 33

34  70S ribosomes (30S + 50S subunit)  S = Svedberg unit (sedimentation rate upon centrifugation)  smaller than eukaryotic ribosome  sediment differently  Consist of proteins and ribosomal RNA  Site of protein synthesis  Contain 16S rRNA on 30S subunit Important for Classification and Identification! 34

35  Storage granules (lipids, carbohydrates, phosphate etc)  Caroxysomes (important for carbon dioxide fixation in photosynthesis)  Gas vesicles for bouyancy  Magnetosomes 35

36  Terminal  Subterminal  Central Spore Vegetative Form Sporulation Germination 36

37  Sporulation is a complex process  Triggered under unfavorable conditions  Very low water content  Spore is multilayered  Resistance through spore coat (protein layer)  Can survive thousands of years  Germination is triggered under favorable conditions  Clostridium spec., Bacillus spec. 37

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39 1. Which of the following is not a distinguishing characteristic of prokaryotic cells? a. They have a single, circular chromosome b. They lack membrane-enclosed organelles c. They have a cell wall containing peptidoglycan d. Their DNA is not associated with histones e. They lack a plasma membrane. 39

40 2. Which of the following is not true of fimbriae? a. They are composed of protein b. They may be used for attachment. c. They are composed of carbohydrates. d. They may be found on gram-negative cells. e. All of above is true. 40

41 Figure 4.22a 41

42  Typically larger (10 – 100  m)  Cell membrane contains sterols  Nucleus  Membrane-enclosed chromosomes  Linear DNA  Nucleolus: site of rRNA synthesis 42

43  Endoplasmatic reticulum  Protein modification  Golgi  Protein modification  Mitochondria  ATP production  Some eukaryotes do not have mitochondria, e.g. Giardia  Chloroplasts  Oxygenic photosynthesis  Peroxisomes  Oxidation Reactions 43

44 44 Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.  How did eukaryotes arise?  DNA similar to archaea’s  Mitochondrial, chloroplast DNA  Similar to bacterial DNA  Endosymbiont theory:  Mitochondria WERE bacteria  Chloroplasts WERE cyanobacteria  Infected or eaten by other species  Ended up living together inside ▪ Endo-sym-biosis

45  80S ribosomes (40S + 60S)  Bigger than prokaryotic ribosome  sediment differently  Consist of proteins and ribosomal RNA  Site of protein synthesis  Contain 18S rRNA subunit  Important for identification 45

46  Flagella  9+2 microtubili  Wave-type movement  Cytoskeleton  Cell Wall  No peptidoglycan!  Instead cellulose (algae) and chitin (fungi) 46

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48  Prokaryotes are cells without a nucleus.  Prokaryotes always have a cell membrane, a nucleoid and 70S ribosomes with 16S rRNA.  Eukaryotes always have a cell membrane, a nucleus, 80S ribosomes with 18S rRNA, and membrane-encoded organelles 48


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