Bacterial Structure and Function PDF

Shapes Are Used to Classify Bacillus: Rod shaped Coccus: Spherical (round) Bacterial Cell...

Shapes Are Used to Classify Bacillus: Rod shaped Coccus: Spherical (round) Bacterial Cell Vibrio: Comma Structure shaped with flagella and Function Spirillum: Spiral shape Spirochete: long spirilla with many tight coils 3 Size of Living Things 1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm 1mm = 1000 µm = 1000000nm 1 µm = 1000nm Cellular organism copies its genetic information then splits into two identical daughter cells 4  Overview of Why study bacterial cell prokaryotic cell. envelope? They are essential structures in bacteria. They are made of chemical components found nowhere else in nature. They may cause symptoms of disease in animals. They are the site of action of some of our most important antibiotics. 5 Bacterial envelope Profile of the bacterial cell envelope Bacterial envelope is a structure that completely surrounds the cell protoplast. (Almost) all bacteria have a cell membrane Protoplast: fungal, plant or Gram-positive cell membrane is a thick gram-positive bacterial cells homogeneous monolayer without a cell wall Gram-negative cell membrane is a thin heterogeneous multilayer  Gram stain Primary function of the bacterial cell Grams stain = a differential stain procedure, different results, + and envelope and membranes (-) To prevent rupture or osmotic lysis of the cell protoplast Lysis of a pair of dividing E. coli cells Prokaryotes - Cell Wall Chemical nature of bacterial cell wall Gram-Positive & Gram-Negative Gram- positive: 90% of cell Bacterial cell wall always wall is made contain murein, which is a up of Peptidoglycan type of peptidoglycan Chemical nature of murein accounts for the function of Gram- the bacterial cell wall negative: 5-10% of cell wall is made up of Murein is only found in the Peptidoglycan cell wall of bacteria E. coli peptidoglycan  Chemical nature of bacterial cell wall Chemical nature of bacterial cell wall Peptidoglycan is made up of 2 amino sugars N-acetyl-glucosamine = G N- acetylmuramic acid = M 4 amino acids L-alanine = L-ala D-glutamic acid = D-glu diaminopimelic acid = DAP D-alanine = D-ala Gram-negative murein. Murein is a polymer of the peptidoglycan subunit. The sugars form the glycan backbone (G- M-G-M-etc.) and the amino acids comprise the peptide side chains of the molecule. Chemical nature of bacterial cell membranes Monomers of peptidoglycan Units added to PG as a pair. NAM: N-acetyl muramic NAG: acid Gram-positive murein has a thicker glycan backbone and N-acetyl there are interpeptide bridges that join amino acid side chains glucosamine (NAG + lactic acid) together. 14  Gram-negative cell membranes include an outer Other characteristics of bacterial cell wall membrane Gram-positive cell membranes contain Outer membrane of Gram-negative has two important properties teichoic acids 1. It protects the cells from permeability by many substances including penicillin and lysozyme. 2. It is the location of lipopolysaccharide (endotoxin) which is toxic for animals. Teichoic acids are thought to stabilize the Gram positive cell membranes and may be used in adherence. Gram-negative cell membranes include an outer membrane Teichoic Acids Gram + only Glycerol, Phosphates, & Ribitol Attachment for some viruses (phages) Participate in flexibility to the cell wall Antigenic determinant: can stimulate an immune response following an infection. Teichoic acid and lipoteichoic Lipopolysaccharide (LPS) acid Found in Gr+ cell wall Endotoxin or Pyrogen – Fever causing – Toxin nomenclature Endo- part of bacteria Exo- excreted into environment Structure – Lipid A – Polysaccharide O Antigen of E. coli, Salmonella G- bacteria only – Alcohol/Acetone removes primary stain during gram’s 21 staining. Teichoic acid and lipoteichoic acid Lipopolysaccharide (LPS) Structure and Function Polymer of phosphate and ribitol or glycerol R: sugar or amino acid Lipoteichoic acid covalently attached to membrane lipids. Major contributor to negative charge of cell exterior. The lipopolysaccharide has three parts: lipid A, core polysaccharide and an O-specific side chain. Appears to function in Ca++ binding The lipid A component may act as an endotoxin, which, if released into the bloodstream, can lead to serious conditions such as fever and toxic shock. May be associated with adherence on The O-specific antigens are carbohydrate chains whose composition often varies between strains of the same species. Proteins incorporated smooth surface Strept mutans tooth decay into the outer membrane and penetrating its entire thickness form channels 22 that allow the passage of water and small molecules to enter the cell.  Correlation of the Gram stain with properties of bacterial cell walls Cell wall Exceptions Property Gram-positive Gram-negative Thickness of membranes thick (20-80 nm) thin (10 nm) Number of layers 1 2-3 Peptidoglycan >50% 10-20% (murein) content Teichoic acids in membranes present absent Protein/lipoprotein 0-3% >50% content Lipopolysaccharide 0 13 content When bacteria are treated with detergent: Sensitivity to penicillin sensitive resistant Protoplast: G+ Spheroplast: G- Sensitivity to lysozyme sensitive resistant L-forms Cell wall Exceptions Cell wall Exceptions Mycobacterium and relatives Gram-positive bacteria have only one cytoplasmic – Wall contains lots of waxy mycolic acids membrane, while gram-negative bacterium have two – Attached covalently to PG membranes: the cytoplasmic and the outer Mycoplasma: no cell wall membrane. Therefore, following the removal of the – Parasites of animals cell wall under the effect of certain conditions, like treatment with antibiotics, protoplasts have only one Archaea: no peptidoglycan membrane, while spheroplasts have two – Pseudomurein and other chemically different membranes. membranes materials (S layer) If protoplasts and spheroplasts grow and divide, they are called L-forms. Mycolic acids are unique long chain fatty acids Unlike mycoplasms, L-forms can revert to the found in the lipid‐rich cell walls of mycobacteria parental form on removal of the cell wall inhibitor 26  Bacterial Plasma Membrane Membrane structure and assembly Separates the cell from its environment. Limits the protoplast Thin and elastic , can be only seen with electron microscope The With the exception of mycoplasma , bacterial cytoplasmic membrane membrane lacks sterol. Phospholipid molecules oriented so that hydrophilic,water-loving bilayer is heads directed outward and hydrophobic ,water-hating tails directed formed by inward. Proteins embedded in two layers of lipids (lipid bilayer) phospholipid molecules FUNCTIONS: made up of Semi-permeable membrane Housing enzymes for cell wall, outer membrane synthesis, assembly and glycerol and secretion of extracytoplasmic and extracellular substances fatty acids Generation of ATP (Adenosine Triphosphate: energy-carrying molecules) Cell motility Mediation of chromosomal segregation during replication Bacterial cytoplasmic membrane Membrane structure and assembly Completely encloses the bacterial cell Phospholipids protoplast arrange themselves Composed of: spontaneously in water: lipid 60% protein “tails” inward; 40% phospholipid glycerol “heads” outward Arranged as a bilayer Section of a cytoplasmic membrane  Membrane structure and assembly Functions of the cytoplasmic membrane Osmotic or permeability barrier: the membrane is impermeable to molecules that The fluid mosaic model of a membrane are charged or greater than The proteins associate with both sides of the molecular membrane, or may imbed in the membrane, or pass through the membrane. weight of 100 Membrane structure and assembly Functions of the cytoplasmic membrane Proteins in the Location of cytoplasmic transport membrane have a systems: to variety of functions including transport import all the and energy needed transformations molecules that are charged or greater than molecular weight 100 by specific The cytoplasmic membrane of E. coli carrier proteins  Transport systems in bacteria Functions of the cytoplasmic membrane Specialized functions involving cell Does not require energy; for hydrophilic molecules wall synthesis, cell division and DNA Requires energy; for replication. some nutrients like amino acids, glucose Functions of the cytoplasmic membrane Cytoplasmic Constituents of Energy Bacterial Cells generation: location of the Cytoplasm electron Genetic material: chromosome and transport Plasmids (DNA) system (ETS) Ribosomes and the ATP synthesizing Inclusions enzyme ATPase The cytoplasm of bacterial cells is gel-like and contains the The Bacterial Chromosome or “Nucleoid” chromosome, ribosomes, various macromolecules and small molecules in water solution. The bacterial chromosome is one long, single molecule of double stranded, helical, supercoiled DNA. In most bacteria, the two ends of the double-stranded DNA covalently bond together to form both a physical and genetic circle. Bacterial DNA released from a “gently lysed” E. coli cell ribosomes DNA (chromosome) Small molecules present in a growing - DNA (deoxyribonucleic acid) is the genetic material of the cell. It is replicated and passed on to progeny cells. bacterial cell Molecules Approximate number of kinds - The bacterial genome is Amino acids, their precursors and derivatives 120 present in the cell within a complex structure, the nucleoid. The nucleoid contains the Nucleotides, their precursors and derivatives 100 genomic DNA, and molecules Fatty acids and their precursors 50 of RNA and proteins. The main proteins of the nucleoid are: Sugars, carbohydrates and their precursors or derivatives 250 RNA polymerase, quinones, porphyrins, vitamins, coenzymes and topoisomerases and histone- prosthetic groups and their precursors 300 like proteins. Ions (PO4, NH3, SO4, etc.) 20  Ribosome Structure and Composition Ribosome Function The prokaryotic ribosome (L) is 70S in size, being Ribosomes function is protein synthesis. Amino acids are composed of a 50S (large) subunit and a and 30S (small) assembled into proteins according to the genetic code on subunit. The eukaryotic ribosome (R) is 80S in size and is the surfaces of ribosomes during the process of translation. composed of a 60S and a 40S subunit. Ribosome Structure and Composition Some inclusions in Bacterial Cells Inclusion Composition Function Glycogen poly-glucose Reserve carbon and energy source Poly-betahydroxybutyric lipid Reserve carbon and acid (PHB) energy source Poly-phosphates polymers of PO4 Reserve phosphate, possibly high-energy PO4 Sulfur globules elemental S Reserve energy and or electrons Magnetosomes magnetite (iron oxide) Provide orientation in magnetic field Gas vesicles protein shells inflated with Provide buoyancy in gases aquatic environments Ribosomes are made of two subunits, a large subunit and a Parasporal crystals protein Produced by endospore- forming Bacilli - toxic to small subunit. Each subunit is made up of RNA and various insects proteins.  Some inclusions in Bacterial Cells Endospore formation is NOT a mechanism of reproduction. Rather it is a mechanism for survival in deleterious environments. During the process of spore formation, one vegetative cell develops into one endospore. The sequential steps of endospore formation in a Bacillus species. The process of endospore formation takes about six hours. Eventually the mature endospore is released from its “mother cell” as a free spore Free endospore Endospore within mother cell Bacterial Inclusions. A. PHB granules; b. a parasporal BT crystal in the sporangium of Vegetative cell Bacillus thuringiensis; c. carboxysomes in Anabaena viriabilis, showing their polyhedral shape; d. sulfur globules in the cytoplasm of Beggiatoa. Under favorable nutritional and environmental conditions, an Endospores are produced as intracellular structures within the cytoplasm endospore germinates into a vegetative cell. of certain bacteria, most notably Bacillus and Clostridium species. Endospore forming bacteria left to right: Clostridium botulinum, Bacillus brevis, Bacillus thuringiensis  Sporulation: the mechanism of spore formation Properties of Endospores Resting (dormant) cells - “cryptobiotic” i.e., show no signs of life…..primarily due to lack of water in the spore Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. Medically-important Properties of Endospores Endospore-forming Bacteria Bacillus anthracis causes anthrax Several unique Bacillus cereus causes food poisoning surface layers not Clostridium tetani causes tetanus found in vegetative cells: exosporium, Clostridium botulinum causes botulism spore coat, cortex, Clostridium perfringens causes food and core wall poisoning and gas gangrene Clostridium difficile causes antibiotic-induced diarrhea and pseudomembranous colitis  Flagella Properties of Endospores Bacteria that are motile have appendages called flagella Highly resistant to Attached by Basal Body heat (boiling), acids, bases, dyes ( don’t A bacteria can have one or many flagella stain) irradiation, disinfectants, antibiotics, etc. 59 Made of Flagellin Properties of Endospores Used for Classification Monotrichous: 1 flagella Lophotrichous: tuft at one end Amphitrichous: tuft at both ends Peritrichous: all around bacteria Parasporal crystal Endospore Spores and parasporal crystals produced by some bacteria are toxic to insects 60  Pili (fimbriae) Short protein appendages Smaller than flagella Adhere bacteria to surfaces(host epithelium) Used in conjugation for Exchange of genetic information 61 Plasmids Conjugation Extra-chromosomal circular DNA Bacterial conjugation is a way by which a bacterial cell transfers genetic material to another bacterial cell. The genetic material multiple copy number that is transferred through bacterial conjugation is a small plasmid, known as F-plasmid (F for fertility factor), that carries genetic information different from that which is already present coding in the chromosomes of the bacterial cell. In fact, the F- - pathogenesis factors plasmid can replicate in the cytoplasm separately from - antibiotic resistance factors the bacterial chromosome. Bacterial replication 64  Prokaryotes - Glycocalyx 2.Polysaccharides firmly attached Types of plasmid to the cell wall. Fertility-F-plasmids. They are capable of conjugation (transfer of genetic Capsules adhere to solid material between bacteria which are touching). surfaces and to nutrients in the environment. Resistance-(R)plasmids, which contain genes that can build a resistance against antibiotics or poisons and help bacteria produce pili. Adhesive power of capsules is a Col-plasmids, which contain genes that determine the production of major factor in the initiation of bacteriocins , proteins that can kill other bacteria. some bacterial diseases. Degradative plasmids, which enable the digestion of unusual substances, e.g., toluene or salicylic acid. Capsule also protect bacteria from being phagocytized by Virulence plasmids, which turn the bacterium into a pathogen (one cells of the hosts immune that causes disease). system. Capsule Glycocalyx – sugar coat irregular secretion of polysaccharides, capsule : tightly bound regular distribution – Protects and prevents from drying, also protects from phagocytes *Slime layer: thin secretion of polysaccharides, and often a significant component of “biofilms”