Cell Structure and Function

Transcription

1 Cell Structure and Function

2 Cell Structure and Function Topics External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification

3 An Infectious Exam Patient with Tuberculosis Ziehl Neelson stain Mycobacterium tuberculosis its function is a factor of its structure Thick waxy outer covering Doesn t stain normally Grows slowly, resides in macrophages Drug sensitivity

4 The Prokaryotic cell So different from the cell you re used to studying! (Eukaryotic cells) No membrane bound organelles Unbound DNA instead of a membrane bound nucleus Cell wall made of peptidoglycan Smaller than a eukaryotic cell Nutrient entrance rate Surface to volume ratio

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6 Bacterial cell structure The prokaryotic cell from the inside out has 3 basic parts: Cytoplasm; fills the cell and houses the internal structures. The envelope which is a general term to refer to the cell wall and membrane. Accessories fun extras that not all bacteria have.

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8 Figure 3.2 Typical prokaryotic cell Inclusions Ribosome Cytoplasm Nucleoid Glycocalyx Cell wall Cytoplasmic membrane Flagellum

9 Cytoplasm Made of water and protein, metabolism occurs here. The nucleoid region Circular loop of naked DNA. Plasmids. Ribosomes Protein factories Different from our own Inclusions- other visible structures Storage granules vacuoles

10 The envelope The envelope serves as the cell boundary and discerning gateway. The envelope can have up 3 layers, depending on what type of cell it is. 1. Outer membrane 2. Cell wall 3. Cytoplasmic membrane

11 Cell wall Gram positive cell wall Thick peptidoglycan (PG) layer Acidic polysaccharides Teichoic acid and lipoteichoic acid Gram-negative cell wall Thin PG layer Outer membrane Lipid polysaccharide Porins

12 Gram-negative cell Contains all 3 layers Outer membrane is a bilayer. Lipopolysaccharide (LPS) layer toward the outside, and a phospholipid layer toward the inside, with proteins through out. Layer is attached to the cell wall by lipoproteins. Useful as protection Is a toxin to mammals

13 Gram positive cell Have teichoic acids sprinkled through out the cell wall, increases integrity of wall Cell wall is very thick compared to gram negative cells Does not have the LPS layer Does not have periplasm

14 Mycoplasma bacteria have no cell wall, which contributes to varied shapes. Fig Scanning electron micrograph of Mycoplasma pneumoniae

15 Periplasmic space, or periplasm- space between the outer membrane and the cytoplasmic membrane. Houses the cell wall as well as binding proteins and enzymes.

16 In general Cell wall a. made of unique material peptidoglycan (murein) b. Site of some antibiotic action (Penicillin stops cell wall formation) c. Cell wall is rigid & determines shape d. Cell wall is porous like a woven basket. Has great strength, but openings. e. Keeps cell from bursting under normal circumstances (turgor pressure) f. Reason for staining differences

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18 Structure of wall Glycan part (polysaccharide) made of long chains of two alternating sugars N-acetlyglucosamine (NAG) N-acetylmuramic acid (NAM) Encircle the cell like hoops on a barrel Held together or cross linked with the peptido part (protein) attached to NAM s only. Protein differs between bacterial species

19 Reason for staining differences

20 Cell Membrane Phospholipid bilayer (+ proteins) -Phosphate group (polar, water loving) -Fatty acids (nonpolar, water phobic) -Remember your integral proteins! receptor sites, enzymes, transport proteins. * no cholesterol in prokaryotic membranes Cell membrane is the site of chemiosmosis to make ATP

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22 Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer Head, which contains phosphate (hydrophilic) Tail (hydrophobic) Phospholipid Integral proteins Cytoplasm Phospholipid bilayer Integral protein Integral protein Peripheral protein

23 Bacterial Cytoplasmic Membranes Function Passive processes Diffusion Facilitated diffusion Osmosis 2012 Pearson Education Inc.

24 Figure 3.18 Passive processes of movement across a cytoplasmic membrane-overview Extracellular fluid Cytoplasm Diffusion through the phospholipid bilayer Facilitated diffusion through a nonspecific channel protein Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in the channel protein Osmosis, the diffusion of water through a specific channel protein or through the phospholipid bilayer

25 Bacterial Cytoplasmic Membranes Function Active processes Active transport Group translocation Substance chemically modified during transport 2012 Pearson Education Inc.

26 Pili and fimbriae Attachment Mating (Conjugation)

27 Accessory structures Appendages Pili and/or flagella Fimbriae Hair like appendages (not cilia) Protein projections that extend all the way from the membrane. Used for attachment, adhesins. S. mutans & teeth, or mucous membranes such as urethra.

28 Figure 3.10 Fimbriae Flagellum Fimbria

29 Pili Special type of fimbria Also known as conjugation pili Longer than other fimbriae but shorter than flagella Bacteria typically have only one or two per cell Mediate the transfer of DNA from one cell to another (conjugation) 2012 Pearson Education Inc.

30 Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another. Fig. 4.8 Three bacteria in the process of conjugating

31 Figure 3.11 Pili Conjugation pilus

32 Flagella Some bacteria don t move, others move with flagella. Structure is very different from eukaryotic flagella. Made of protein flagellin Propeller action vs. wavelike action No 9+2 micro tubular arrangement Prokaryotic Eukaryotic

33 Figure 3.6 Proximal structure of bacterial flagella-overview Filament Direction of rotation during run Rod Peptidoglycan layer (cell wall) Protein rings Cytoplasm Cytoplasmic membrane Filament Gram + Gram Basal body Outer protein rings Rod Integral protein Inner protein rings Integral protein Cytoplasm Outer membrane Peptidoglycan layer Cytoplasmic membrane Cell wall

34 Process of Movement (Run and Tumble method) 1. Taxis the movement of a bacterium toward or away from a particular stimulus. Toward (+), away ( ) Examples: Chemotaxis Aerotaxis Phototaxis

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36 Number/location of flagella are distinguishing characters 1. One flagella = monotrichous 2. Cluster at one end = lophotrichous 3. both ends = amphitrichous 4. Covering the cell = peritrichous

37 Glycocalyx Capsule Protects bacteria from immune cells Slime layer Enable attachment and aggregation of bacterial cells

38 Glycocalyx/Capsule/Slime layer Not on all bacterial cells but if present it s the outermost layer. Capsule tends to be thick, rigid and smooth. Slime layer is thinner & less rigid, globular *Extra layer guards against desiccation *Protects the cell from phagocytosis (S. pneumoniae) *Can be used as attachment such as in tooth decay bacteria (S. mutans)

39 Figure 3.5 Glycocalyces-overview Glycocalyx (capsule) Glycocalyx (slime layer)

40 The slime layer is associated with the formation of biofilms, which are typically found on teeth. Fig Biofilm

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42 During nutrient depleted conditions, some bacteria (vegetative cell) form into an endospore in order to survive. Fig Microscopic picture of an endospore formation

43 Survival Structures A. Endospores (sporogenesis) 1. Made when the environment goes bad 2. Endospore contains all the important parts of the cell. 3. Only made by certain bacteria (Bacillus and Clostridium) 4. Not reproduction!! No increase in # s 5. Autoclaving is the only way to destroy spores. 121 Celsius/15-20lbs. per square inch/15-20 min.

44 Figure 3.24 The formation of an endospore-overview Cell wall Cytoplasmic membrane DNA is replicated. DNA A cortex of calcium and dipicolinic acid is deposited between the membranes. Cortex Vegetative cell DNA aligns along the cell s long axis. Spore coat forms around endospore. Spore coat Cytoplasmic membrane invaginates to form forespore. Forespore Endospore matures: completion of spore coat and increase in resistance to heat and chemicals by unknown process. Outer spore coat Endospore Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell s DNA disintegrates. First membrane Second membrane Endospore is released from original cell. Outer spore coat

45 Clostridium tetani

46 Cell shapes Coccus Rod or bacillus Curved or spiral Cell arrangements Cell size

47 Cell arrangements Single cells found by themselves. Diplo - cells in pairs. Diplococcus, Diplobacillus Strepto cells in chains. Streptococcus, Streptobacillus Staphylo cells in grape like clusters. Staphylococcus

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50 Classification Phenotypic methods Molecular methods Taxonomic scheme Unique groups

51 Phenotypic methods Cell morphology -staining Biochemical test enzyme test

52 Molecular methods DNA sequence 16S RNA Protein sequence

53 The methods of classification have allowed bacteria to be grouped into different divisions and classes. Table 4.3 Major taxonomic groups of bacteria

54 An example of how medically important families and genera of bacterial are characterized. Table 4.4 Medically important families and genera of bacteria.