Cell Structure and Function PDF

Chapter 4/5 Cell Structure and Function Cell Structure and Function • Topics – External Structures – Cell Envelope – Internal Structures – Cell Shapes, Arrangement, and Sizes – Classification An Infectious Exam • Patient with Tuberculosis – Ziehl Neelson stain – Mycobacterium tuberculosis its f...

Chapter 4/5 Cell Structure and Function Cell Structure and Function • Topics – External Structures – Cell Envelope – Internal Structures – Cell Shapes, Arrangement, and Sizes – Classification 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 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 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. Figure 3.2 Typical prokaryotic cell Inclusions Ribosome Cytoplasm Flagellum Nucleoid Glycocalyx Cell wall Cytoplasmic membrane 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 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 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 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 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 Mycoplasma bacteria have no cell wall, which contributes to varied shapes. Fig. 4.15 Scanning electron micrograph of Mycoplasma pneumoniae • Periplasmic space, or periplasm- space between the outer membrane and the cytoplasmic membrane. Houses the cell wall as well as binding proteins and enzymes. Cell wall In general 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 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 Reason for staining differences 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 Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer Head, which contains phosphate (hydrophilic) Phospholipid Tail (hydrophobic) Integral proteins Cytoplasm Integral protein Phospholipid bilayer Peripheral protein Integral protein Bacterial Cytoplasmic Membranes • Function – Passive processes • Diffusion • Facilitated diffusion • Osmosis © 2012 Pearson Education Inc. 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 Osmosis, through a permease specific for one chemical; binding of substrate causes shape change in the channel protein the diffusion of water through a specific channel protein or through the phospholipid bilayer Bacterial Cytoplasmic Membranes • Function – Active processes • Active transport – Group translocation • Substance chemically modified during transport © 2012 Pearson Education Inc. Pili and fimbriae • Attachment • Mating (Conjugation) 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. Figure 3.10 Fimbriae Flagellum Fimbria • 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. 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 Figure 3.11 Pili Conjugation pilus • 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 Figure 3.6 Proximal structure of bacterial flagella-overview Filament Direction of rotation during run Rod Peptidoglycan layer (cell wall) Protein rings Cytoplasmic membrane Cytoplasm Filament Gram + Outer protein rings Rod Gram − Basal body Outer membrane Peptidoglycan layer Integral protein Inner protein rings Integral protein Cytoplasm Cytoplasmic membrane Cell wall 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 Number/location of flagella are distinguishing characters 1. One flagella = monotrichous 2. Cluster at one end = lophotrichous 3. Flagella @ both ends = amphitrichous 4. Covering the cell = peritrichous Glycocalyx • Capsule – Protects bacteria from immune cells • Slime layer – Enable attachment and aggregation of bacterial cells 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) Figure 3.5 Glycocalyces-overview Glycocalyx (capsule) Glycocalyx (slime layer) The slime layer is associated with the formation of biofilms, which are typically found on teeth. Fig. 4.11 Biofilm During nutrient depleted conditions, some bacteria (vegetative cell) form into an endospore in order to survive. Fig. 4.21 Microscopic picture of an endospore formation • 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. 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 Spore coat forms around endospore. DNA aligns along the cell’s long axis. Cytoplasmic membrane invaginates to form forespore. Forespore Endospore matures: completion of spore coat and increase in resistance to heat and chemicals by unknown process. Endospore is released from original cell. Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell’s DNA disintegrates. First membrane Second membrane Spore coat Outer spore coat Endospore Outer spore coat Clostridium tetani Cell shapes • • • • • Coccus Rod or bacillus Curved or spiral Cell arrangements Cell size • 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 Classification • • • • Phenotypic methods Molecular methods Taxonomic scheme Unique groups Phenotypic methods • Cell morphology -staining • Biochemical test – enzyme test Molecular methods • DNA sequence • 16S RNA • Protein sequence The methods of classification have allowed bacteria to be grouped into different divisions and classes. Table 4.3 Major taxonomic groups of bacteria An example of how medically important families and genera of bacterial are characterized. Table 4.4 Medically important families and genera of bacteria.