Bacterial Cell Structure and Function PDF

Bacterial cell Small microorganisms with a simple form of cellular organization described as prokaryotic cells. -Do not contain a membrane – bound nucleus. -Their hereditary material is suspended in a portion of cytoplasm called Nucleoid or Nuclear region ( no nuclear membrane)....

Bacterial cell Small microorganisms with a simple form of cellular organization described as prokaryotic cells. -Do not contain a membrane – bound nucleus. -Their hereditary material is suspended in a portion of cytoplasm called Nucleoid or Nuclear region ( no nuclear membrane). -They are also devoid of mitochondria and other membrane bound organelles.  Bacteria are among the most widely distributed forms of life They are found in air , water , food, and soil etc. They are also found in the external and internal bodies of the human and animals and plants Bacterial morphology Bacteria are differentiated into major categories based on: Microscopic observation of their morphological features such as shape , size , arrangement and staining characteristics Most bacteria range in size from 0.2- 1.2 m in width and 0.4 -14 um in length  Bacterial shapes and arrangement : A)Cocci : are spherical organisms with a wide variety of arrangements e.g.: 1 Diplococci ; pairs of cells. 2Irregular grape – like clusters , e.g: staphylococci. 3 Chains of four or more e.g. Streptococci B- Bacilli : are rod – shaped organisms C- Spiral bacteria Bacterial Structure and function  Glycocalyx (Capsules, Cell Envelope Slime layers) Cell Wall Cell Membrane Ribosomes, Granules, Prokaryotic Cytoplasm Nucleoid/Chromosom Cell e (Plasmids) Flagella, Appendages Pili/Fimbriae 9 Pili (pl), pilus (s) – Only found in gram negative bacteria – hollow, hair like structures of protein larger and more sparse than fimbriae. – allow bacteria to attach to other cells (organ of attachment). – sex pilus:- transfer genetic material from one bacterial cell to another (conjugation). fimbriae (pl) fimbria (s) – Adhesion to cells and surfaces – Responsible for biofilms. function in adhesion to other cells and surfaces 12  Conjugation 13 joins bacterial cells for DNA transfer (conjugation)  Bacterial Flagella Provide motility Much longer than cell 14  It is thread like appendages Organ of locomotion and made of protein subunit called flagellin. Have 3 morphological parts a)Filament – long, thin, helical structure composed of proteins b) Hook (universal joint) A short curved structure Wider region at the base of flagella Acts as universal joint b/n the motor in the basal structure and the flagellum c) Basal body A system of rings and rods imbedded in the cell envelope In gram negative bacteria, has two sets of rings  L rings  P rings Attached to the outer membrane of cell envelope  S rings Attached to cytoplasmic membrane  M rings 17  In gram positive, has one set of rings  S rings Attached to cytoplasmic membrane  M rings Comprise the motor apparatus =are the flagellar powerhouse for activating the filament Rings anchors the flagella to CM and in some cases to the cell wall as well.  Importance of Flagella Are not essential for survival of the cell Attachment to surfaces (epithelial tissue) Motility as a virulence factor Diagnostic value and Identification antigenic nature Are highly antigenic (H antigens), and some of the immune responses to infection are directed against these proteins.  arrangement  glycocalyx Coating of bacteria, external to the cell wall, made of sugars and/or proteins (Bacillus) 2 types 1. capsule - highly organized, tightly attached 2. slime layer - loosely organized and attached non uniform in density and thickness functions – Attachment to other bacteria or host tissues – inhibits killing by white blood cells and detergents – Receptor – Some produce biofilm that protects from antibiotics and host defense( tooth plaques, S. mutans) – Capsule, slime-unnecessary for growth but need for survival  Cell wall Thick and relatively rigid layer next to CM. Components are unique to bacteria Contain strong activator of immune response Structural components and their function used for classification crucial for growth and division Supports and protect the fragile cytoplasmic membrane and the contents it encloses Compounds that interfere with synthesis are lethal and include many antibiotics Gets special attention 1. They are an essential structure for viability 2. They are composed of unique components found nowhere else in nature. 3. It is one of the most important sites for attack by antibiotics. 4. They provide ligands for adherence and receptor sites for drugs or viruses. 5. They cause symptoms of disease (toxic). 6. They provide for immunological distinction and immunological variation among strains of bacteria e.g.,LPS, M protein, TA,  Grouping based on cell wall composition 1. Gram positive cells (e.g. Bacillus subtilis) 2. Gram negative cells (e.g. E. coli) 3. Bacteria with chemically unique cell walls (e.g. Mycobaceterium tuberculosis) 4. Bacteria without cell walls (e.g. Mycoplasma)  Rigidity of cell wall is due to the presence of peptidoglycan Peptidoglycan Back bone of the cell wall (gives rigidity) Made of rope like linear polysaccharides cross links by peptides Made of 1. Two amino sugars:- a. N-acetyl glucose amine b. N-acetyl muramic acid 2. Peptides L-alanine D-alanine D- glutamic acid 24 Figure. Assembly of the peptidoglycan 25  No. of the tetrapeptide side chain and degree of the peptide cross-bridges vary from species to species The tetrapeptide of all species, however, have certain important features in common. Most have L-alanine at position 1 D-glutamate at position 2 D-alanine at position 4 Position 3 is the most variable one Most gram negative bacteria have diaminopimelic acid Most gram positive bacteria usually have L-lysine at position 3; however, some may have DAP or another amino acid. Muramic acid, D-amino acids, diaminopimelic acid not synthesized by mammals  Cell wall of Gram positive bacteria Thick peptidoglycan Peptidoglycan contain TA, LTA, M proteins, C polysaccharide LTA anchored to the cell membrane TA and LTA antigenic (classification) -used as attachment organ (virulent factor) - Initiate host response  Cell wall of gram negative Structurally more complex Contain thin peptidoglycan Contain outer membrane No TA/LTA Contain wide periplasmic space containing:- -variety of hydrolytic enzyme which are used for metabolism/virulence factors (phosphatase, Beta lactamase, lipase, protease, collagenase etc.,) -Transport proteins, binding proteins Outer membrane contains -Lipopolysacchrides (LPS)- Endotoxin -Powerful stimulator of immune response [activate B cells, macrophages, dendric cells and cause release of high amount of cytokines(IL-1,IL-2, TNF-) which cause fever-shock] - Contain structural proteins, receptors  Gram negative cell wall Lipopolysaccharide Porin proteins Outer membrane Periplasmic space Peptidoglycan Cytoplasmic membrane Cytoplasm 32 32 080506 Möllby Lipopolysaccharide = endotoxin O-antigen Core poly- saccharid e Lipid A is anchored in outer mem- brane (OM) 33 33 LPS Made of Lipid A, Core polysaccharide and O antigen Lipid A is the toxic part and essential for bacterial viability LPS is used to classify bacteria Lipid A is similar for all gram negative bacteria. The core is same for species of bacteria The O antigens distinguishes serotypes (strains) Lipooligosaccharide which is present in Niesseria spps, lack O antigen portion of LPS 34  The acid fast cell wall Resemble Gram positive cell wall Acid-fast bacteria have a cell wall with a relatively impermeable cell wall containing a waxy lipid called mycolic acid. Mycolic acids confer resistance to Desiccation  Most antibiotics  Phagocytosis  Contributes to pathogenicity Lipoarabinomannan Complex cell wall structure of Mycobacteria  Cell wall deficient forms L- forms ( Lister Institute where discovered) – Bacteria loses cell wall during the life cycle Result of a mutation in cell wall forming genes Induced by treating with lysozyme or penicillin which disrupts the cell wall – Protoplast- G + bacterium with no cellwall, only a cell membrane Fragile, easily lysed – Spheroplast- G – bacterium loses peptidoglycan, but has outer membrane Less fragile but weakened.  Cytoplasmi c membrane Lipid bilayer Semipermeable barrier Contains: Structural proteins Transport proteins Electron transport system (respiration) Enzymes Ion pumps Flagellum anchor site of DNA synthesis 39 39 080506 Möllby  Chromosome single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid  Ribosomes made of 60% ribosomal RNA & 40% protein consist of 2 subunits: large & small ⮩ 70’S procaryotic differ from eucaryotic ribosomes in size & number of proteins site of protein synthesis Target of some drugs  Inclusions, granules intracellular storage bodies vary in size, number & content bacterial cell can use them when environmental sources are depleted Examples: glycogen, poly- - hydroxybutyrate, gas vesicles for floating, sulfur and polyphosphate granules  plasmids Plasmids carry the genes for production of :- Antibiotic resistance, which is mediated by a variety of enzymes Resistance to heavy metals such as mercury (the active component of some antiseptics, Resistance to ultraviolet light, Pili (fimbriae), which mediate the adherence of bacteria to epithelial cells Toxins (Exotoxins, including several enterotoxins). 43  Endospores Resting, dormant cells produced by some G+ genera: Clostridium, Bacillus & Sporosarcina Have a 2-phase life cycle – vegetative cell & endospore sporulation -formation of endospores germination- return to vegetative growth hardiest of all life forms withstand extremes in heat, drying, freezing, radiation & chemicals not a means reproduction of 44  endospores resistance linked to high levels of calcium & dipicolinic acid dehydrated, metabolically inactive thick coat pressurized steam at 121oC for 20-30 minutes will destroy. Locations of Endospores 47 Figure 11.8b Spore is used for classification a. position can be central, sub terminal or terminal b. Shape can be spherical or oval central or sub terminal spores: Clostricium welchii, Clostridium sporogenes oval and terminal spores: Clostridium tertium spherical and terminal spores: Clostridium tetani 48