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Online Counseling Resource YCMOU ELearning Drive…

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1 Online Counseling Resource YCMOU ELearning Drive…
14-Apr-17 Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – , India © 2006, YCMOU. All Rights Reserved.

2 OC-SEP041-CP01-02 Introduction
14-Apr-17 OC-SEP041-CP01-02 Introduction Programmes and Courses SEP – SBT041 – Unit 01 SEP – SBI041 – Unit 01 SEP – SGS041 – Unit 01 © 2006, YCMOU. All Rights Reserved.

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14-Apr-17 Credits Academic Inputs by Mrs. Rasika Bhore M.sc (Microbiology) © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

4 How to Use This Resource
14-Apr-17 How to Use This Resource Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling. Discussion about students difficulties or tutorial with assignments should follow the lecture for about minutes. Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student. Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam. Appear several times, for all the Self-Tests, available for this course. Student can use handouts for last minutes preparation just before end exam. © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

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14-Apr-17 Learning Objectives After studying this module, you should be able to: Discuss the various forms of bacteria. Describe special features of bacteria like capsules, cell wall & cell membrane. © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

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Introduction The peptidoglycan cell wall confers shape on bacterial cell wall. Different shapes differentiate the groups of bacteria. Bacterial envelope can have as many as three layers. Moving from the outside toward inside we encounter an outer membrane, a cell wall & a cytoplasmic membrane. The three major groups of bacteria i.e. gram positive, gram negative & mycoplasma’s differ with respect to the number of layers that comprise their envelope. © 2007, YCMOU. All Rights Reserved.

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Forms of Bacteria Bacteria exist in different shapes according to which they are classified into following groups: Cocci Bacilli Spirilla Vibrios © 2007, YCMOU. All Rights Reserved.

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Cocci Singularly called as coccus. Spherical or round in shape. These bacteria when occur singly called micrococci, in pairs called diplococci, in groups of four tetracocci, in cubical arrangement of eight or more sarcinae, in irregular clumps staphylococci & in bead like chain streptococci. Examples are staphylococcus aureus, Diplococcus pneumoniae . © 2007, YCMOU. All Rights Reserved.

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Bacilli They are rod like bacteria. They generally occur singly, but may occasionally found in pairs (diplobacilli) or chains ( streptobacilli). Examples are Corynebacterium diphtheriae, Mycobacterium leprae, Clostridium tetani etc. © 2007, YCMOU. All Rights Reserved.

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Spirilla These are also called spirochetes. These are spiral shaped & motile bacteria. Examples are Treponema pallidum. © 2007, YCMOU. All Rights Reserved.

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Vibrios These are comma shaped or bent-rod like bacteria. E.g. Vibrio cholerae Vibrios © 2007, YCMOU. All Rights Reserved.

12 A Typical Bacterial Cell
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The Cell Envelope The cell envelope is a descriptive term for the several layers of material that enclose the protoplasm of the cell. The cell protoplasm (cytoplasm) is surrounded by the plasma membrane, a cell wall and a capsule. All cells have a membrane, which is the essential and definitive characteristic of a "cell". Almost all prokaryotes have a cell wall to prevent damage to the underlying protoplast. Outside the cell wall, foremost as a surface structure, may be a polysaccharide capsule or glycocalyx. © 2007, YCMOU. All Rights Reserved.

14 Capsules & Slime Layers
Most prokaryotes contain some sort of a polysaccharide layer outside of the cell wall polymer generally referred as capsule. A true capsule (shown in figure) is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is a called a slime layer or a biofilm. A type of capsule found in bacteria called a glycocalyx, a tangled polysaccharide films that may certainly present on the surfaces of bacterial cells, but which cannot be detected visually. © 2007, YCMOU. All Rights Reserved.

15 Chemical Composition of Capsules
Bacterium Capsule composition Structural subunits Gram-positive Bacteria Bacillus anthracis polypeptide (polyglutamic acid) D-glutamic acid Bacillus megaterium polypeptide and polysaccharide D-glutamic acid, amino sugars, sugars Streptococcus mutans polysaccharide (dextran) glucose Streptococcus pneumoniae polysaccharides sugars, amino sugars, uronic acids Streptococcus pyogenes polysaccharide (hyaluronic acid) N-acetyl-glucosamine and glucuronic acid Gram-negative Bacteria Acetobacter xylinum (cellulose) glucose Escherichia coli polysaccharide (colonic acid) glucose, galactose, fucose glucuronic acid Pseudomonas aeruginosa mannuronic acid Azotobacter vinelandii glucuronic acid Agrobacterium tumefaciens (glucan) glucose © 2007, YCMOU. All Rights Reserved.

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Functions of Capsules Capsules, slime layers, and glycocalyx often mediate adherence of cells to surfaces. Protect bacterial cells from engulfment by predatory protozoa or white blood cells (phagocytes), or from attack by antimicrobial agents of plant or animal origin. Capsules in certain soil bacteria protect cells from perennial effects of drying or desiccation. Capsular materials (e.g. dextrans) when overproduced, act as reservoir of carbohydrate for subsequent metabolism. © 2007, YCMOU. All Rights Reserved.

17 Cell Wall Is A Special Structure……
cell walls of bacteria deserve special attention for several reasons: They are an essential structure for viability. They are composed of unique components found nowhere else in nature. They are one of the most important sites for attack by antibiotics. They provide ligands for adherence and receptor sites for drugs or viruses. They cause symptoms of disease in animals. They provide for immunological distinction and immunological variation among strains of bacteria. © 2007, YCMOU. All Rights Reserved.

18 © 2007, YCMOU. All Rights Reserved.
Structure of Cell Wall Most prokaryotes have a rigid cell wall. It protects the cell protoplast from mechanical damage and from osmotic rupture. Cell wall made of porous, rigid material murein that has high tensile strength & is the ubiquitous component of bacterial cell walls. Murein is a unique type of peptidoglycan, a polymer of disaccharides (glycan) cross-linked by short chains of amino acids (peptide). All Bacterial peptidoglycans contain N-acetylmuramic acid, which is the definitive component of murein. The cell walls of Archaea composed of peptidoglycan molecules, but never do they contain murein which distinguishes them from other bacteria. © 2007, YCMOU. All Rights Reserved.

19 Gram Positive Cell Wall
In the Gram-positive Bacteria (that retain the purple crystal violet dye in Gram-staining), the cell wall consists of several layers of peptidoglycan. Running perpendicular to the peptidoglycan sheets is a group of molecules called teichoic acids which are unique to the Gram-positive cell wall. © 2007, YCMOU. All Rights Reserved.

20 Peptidoglycan Sheet of Staphylococcus aureus
G = N-acetyl-glucosamine M = N-acetyl-muramic acid L-ala = L-alanine D-ala = D-alanine D-glu = D-glutamic acid L-lys = L-lysine. © 2007, YCMOU. All Rights Reserved.

21 © 2007, YCMOU. All Rights Reserved.
Teichoic Acids Teichoic acids are linear polymers of polyglycerol or polyribitol substituted with phosphates and a few amino acids and sugars. They are occasionally anchored to the plasma membrane (called lipoteichoic acid, LTA). They are essential to viability of Gram-positive bacteria in the wild. They provide a channel of regularly-oriented negative charges for threading positively charged substances through the complicated peptidoglycan network. They are in some way involved in the regulation and assembly of muramic acid subunits on the outside of the plasma membrane. There are instances, particularly in the streptococci, wherein teichoic acids have been implicated in the adherence of the bacteria to tissue surfaces. © 2007, YCMOU. All Rights Reserved.

22 Gram Negative Cell Wall
In the Gram-negative Bacteria (which do not retain the crystal violet), the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin), which is toxic to animals. In Gram-negative bacteria the outer membrane is usually thought of as part of the cell wall. © 2007, YCMOU. All Rights Reserved.

23 Gram Negative Cell Wall
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24 Outer Membrane of Gram Negative Bacteria
outer membrane, is a discrete lipid bilayered structure intercalated with proteins on the outside of the peptidoglycan sheet. The inner face of the outer membrane is composed of phospholipids. It serves as a permeability barrier. © 2007, YCMOU. All Rights Reserved.

25 LPS (lipopolysaccharide)
The outer face of the outer membrane is mainly formed by a different type of amphiphilic molecule which is composed of lipopolysaccharide (LPS). Outer membrane proteins usually traverse the membrane and in one case, anchor the outer membrane to the underlying peptidoglycan sheet. The LPS molecule that constitutes the outer face of the outer membrane is composed of a hydrophobic region, called Lipid A, that is attached to a hydrophilic linear polysaccharide region, consisting of the core polysaccharide and the O-specific polysaccharide. © 2007, YCMOU. All Rights Reserved.

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Arrangement of LPS The Lipid A head of the molecule inserts into the interior of the membrane, and the polysaccharide tail of the molecule faces the aqueous environment. Where the tail of the molecule inserts into the head there is an accumulation of negative charges such that a magnesium cation is chelated between adjacent LPS molecules. This provides the lateral stability for the outer membrane. © 2007, YCMOU. All Rights Reserved.

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Toxicity of LPS Endotoxins or LPS may play a role in infection by any Gram-negative bacterium, are toxic to animals. When injected in small amounts endotoxin activates macrophages to produce pyrogens, activates the complement cascade causing inflammation, and activates blood factors resulting in intravascular coagulation and hemorrhage. The toxic component of endotoxin (LPS) is Lipid A. The O-specific polysaccharide may provide ligands for bacterial attachment and confer some resistance to phagocytosis. Variation in the exact sugar content of the O polysaccharide accounts for multiple antigenic types (serotypes), thus they nonetheless contribute to virulence of Gram-negative bacteria. © 2007, YCMOU. All Rights Reserved.

28 Cell Wall Proteins of E.coli
In E.coli, about 400,00 copies of the Braun lipoprotein anchors the outer membrane to peptidoglycan (murein) sheet. A group of trimeric proteins called porins form pores of a fixed diameter through the lipid bilayer of the membrane. Porins are designed to allow passage of nutrients through the barrier of the outer membrane, but to exclude passage of harmful & hydrophobic substances (such as bile salts) from the environment. The omp C and omp F porins in E. coli allow passage of hydrophilic molecules up to mw of about 750 daltons. The ubiquitous omp A protein in the outer membrane of E. coli may function in uptake of specific ions, but it is also a receptor for the F pilus and an attachment site for bacterial viruses. © 2007, YCMOU. All Rights Reserved.

29 Comparison of Two Cell Types
Property  Gram-positive Gram-negative Thickness of wall  thick (20-80 nm) thin (10 nm) Number of layers  2 Peptidoglycan (murein) content  >50% 10-20% Teichoic acids in wall present absent Lipid and lipoprotein content  0-3% 58% Protein content  9% Lipopolysaccharide content  13% Sensitivity to Penicillin G  yes no (1) Sensitivity to lysozyme no (2) © 2007, YCMOU. All Rights Reserved.

30 © 2007, YCMOU. All Rights Reserved.
S- layers of Cell Wall S-layer crystalline proteins form the outermost cell envelope component of a broad spectrum of bacteria and archaea.  S-layers are composed of a protein or glycoprotein (Mw kDa) and exhibit either oblique, square or hexagonal lattice symmetry. S-layers are generally 5 to 10 nm thick and show pores of identical size (diameter nm) and morphology. Isolated S-layer proteins have the intrinsic property to recrystallize on a surfaces including silicon, metals and polymers, and to interfaces such as planar lipid films and liposomes. The well defined arrangement of functional groups on S-layer lattices allows the binding of molecules and particles in defined regular arrays. © 2007, YCMOU. All Rights Reserved.

31 © 2007, YCMOU. All Rights Reserved.
Functions of S-Layers The S-layer may protect bacteria from harmful enzymes or changes in pH. It may contribute to virulence by protecting the bacterium against complement attack and phagocytosis. It is thought to protect E. coli from attack by the predatory bacterium, Bdellovibrio. S-layer can function as an adhesin, enabling the bacterium to adhere to host cell membranes and environmental surfaces in order to colonize. © 2007, YCMOU. All Rights Reserved.

32 Cell Wall Less Forms A few bacteria are able to live or exist without a cell wall. The mycoplasmas are a group of bacteria that lack a cell wall. E.g. Mycobacterium tuberculosis, M. Leprae etc. They have sterol-like molecules incorporated into their membranes and they are usually inhabitants of osmotically-protected environments. Sometimes, under the pressure of antibiotic therapy, pathogenic bacteria can revert to cell wall-less forms (called spheroplasts or protoplasts) and persist or survive in osmotically-protected tissues. When the antibiotic is withdrawn from therapy the organisms may regrow their cell walls and reinfect unprotected tissues.

33 Cell Membrane/Plasma Membrane
The plasma membrane, also called the cytoplasmic membrane, is the most dynamic structure of a prokaryotic cell. Its main function is a s a selective permeability barrier that regulates the passage of substances into and out of the cell. The plasma membrane is the definitive structure of a cell that sequesters the molecules of life in a unit, separating it from the environment. The bacterial membrane allows passage of water and uncharged molecules up to mw of about 100 daltons, but does not allow passage of larger molecules or any charged substances except by means special membrane transport processes and transport systems. © 2007, YCMOU. All Rights Reserved.

34 Structure of Plasma Membrane
Bacterial membranes are composed of 40 % phospholipid and 60 % protein. The phospholipids are amphoteric molecules with a polar hydrophilic glycerol "head" attached via an ester bond to two nonpolar hydrophobic fatty acid tails, which naturally form a bilayer in aqueous environments. Various structural and enzymatic proteins are dispersed within a bilayer which carry out most membrane functions. © 2007, YCMOU. All Rights Reserved.

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Fluid Mosaic Model Some membrane proteins are located and function on one or another side of the membrane. Most proteins are partly inserted into the membrane, or possibly even traverse the membrane as channels from the outside to the inside. The arrangement of proteins and lipids to form a membrane is called the fluid mosaic model. © 2007, YCMOU. All Rights Reserved.

36 Functions of Plasma Membrane
Osmotic or permeability barrier. Location of transport systems for specific solutes (nutrients and ions). Energy generating functions, involving respiratory and photosynthetic electron transport systems, establishment of proton motive force, and transmembranous, ATP-synthesizing ATPase. Synthesis of membrane lipids. Synthesis of murein (cell wall peptidoglycan). Assembly and secretion of extracytoplasmic proteins. Coordination of DNA replication and segregation with septum formation and cell division. Chemotaxis. Location of specialized enzyme system. © 2007, YCMOU. All Rights Reserved.

37 What We Learn…………. True capsule is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is a called a slime layer or a biofilm. Capsules play an important role in attachment & prevention of bacteria from phagocytosis. Gram positive bacterial cell wall consists of several layers of peptidoglycan & teichoic acid is a special feature. Gram negative bacterial cell wall consists of a single layer of peptidoglycan & a unique component LPS is present. Mycoplasmas are cell wall lack forms. Proteins & lipids constitutes a Fluid Mosaic Model of bacterial cell membrane.

38 Critical Thinking Questions
14-Apr-17 Critical Thinking Questions Gram positive & gram negative bacteria both produces toxins. Who's toxin is more powerful, how? Plasma membrane act as a permeability barrier & do not allow the large molecular weight substances to pass through. How these nutrients enter inside the membrane? © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

39 Tips For Critical Thinking Questions
Gram positive bacteria produce exotoxins which has high potency. It is an enzyme which interferes ADP-ribosylation. Cell membrane has special transport systems which can pass the large nutrients & ions through the membrane. These are facilitated diffusion, active transport & group translocation.

40 © 2007, YCMOU. All Rights Reserved.
14-Apr-17 Study Tips Book Title: Microbiology Author: Robert Bauman Book Title: Introduction to Microbiology Author: John L. Ingraham Book Title: Cell Biology Author: S.Chand Publication © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

41 © 2007, YCMOU. All Rights Reserved.
14-Apr-17 Acknowledgement Structures & functions of prokaryotes © 2007, YCMOU. All Rights Reserved. © 2006, YCMOU. All Rights Reserved.

42 End of the Presentation
14-Apr-17 End of the Presentation Thank You! © 2006, YCMOU. All Rights Reserved.


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