Architechture of microbial cell

It explains about cell organelles....

1. By :- Vikas C J ARCHITECTURE OF MICROBIAL CELL

2. Contents Introduction Classification of bacteria Structure of bacteria Conclusion Reference

3. Cells Smallest living unit Most are microscopic

4. Cell size: Dimensions of most bacterial cells: Diameter : 0.2 to 2.0 m m. Human red blood cell is about 7.5-10 m m in diameter. Length : 2 to 8 m m. Some cyanobacteria are up to 60 m m long. Bacterial cells have large surface to volume ratios. Therefore all parts of the cell: Are close to the surface. Can be quickly reached by nutrients

5. Cell Types Prokaryotic Eukaryotic

6. Distinguishing Features of Prokaryotic Cells: 1. DNA is: Not enclosed within a nuclear membrane . A single circular chromosome. Not associated with histone proteins. 2. Lack membrane-enclosed organelles like mitochondria, chloroplasts, Golgi, etc. 3. Cell walls usually contain peptidoglycan , a complex polysaccharide. 4. Divide by binary fission

7. Distinguishing Features of Eukaryotic Cells: 1. DNA is: Enclosed within a nuclear membrane . Several linear chromosomes. Associated with histones and other proteins. 2. Have membrane-enclosed organelles like mitochondria, chloroplasts, Golgi, endoplasmic reticulum, etc. 3. Divide by mitosis.

8. Differences between Prokaryotes and Eukaryotes Prokaryotes Eukaryotes Cell size 0.2-2 um in diameter 10-100 um in diameter Nucleus Absent Present Membranous Organelles Absent Present Cell Wall Chemically complex When present, simple Ribosomes Smaller (70S) Larger (80S) in cell 70S in organelles DNA Single circular Multiple linear chromosome chromosomes (histones) Cell Division Binary fission Mitosis Cytoskeleton Absent Present

9. Structure of Prokaryotes

10. BACTERIA Micrscopic Unicellular , organisms  belonging to Kingdom monera  that possess a prokaryotic cell structure, which means their DNA (usually circular) can be found throughout the  cytoplasm rather than within a membrane-bound nucleus. They reproduce by fission or by forming spores. They can practically live everywhere. They can inhabit all kinds of environment, such as in soil, acidic hot springs, radioactive waste, seawater, deep in the Earth's crust, in stratosphere, .

11. The electronic microscope studies have revealed that the ultra structure of bacterial cell possesses the following structure Capsule or slim layer Cell wall Plasma membrane Flagella and fibriae and pilus Cytoplasm which includes ribosomes , mesosomes , fat vacuoles , inclusion bodies and nucleoides .

12. CAPSULE Certain bacteria like diplococcus and pneumococcal are externally covered by a layer of that layer is called capsule . Glycocalyx - Polysaccharide on external surface Forms an envelope around the cell wall and can be observed under light microscope. Chemically capsules are made up of proteins, polysaccharide and lipids The bacterial capsule is species specific and can be used for immunological detections. amount these polymers vary with bacterial species. It is sticky in nature ,secreted by the cell which gets firmly attached to the cell wall. If the substances are unorganized and loosely attached to cell wall, - slime layer. Many gram positive and gram negative bacteria have a regular structured layer called an S-layer on their surface. These are very common among Archea . where they may be the only wall structure outside the plasma membrane.

13. Functions of Capsule Prevent attachment of bacteiophages . Prevents bacterial cell against desiccation. Survive in natural environment –sticky property. Prevents from phagocytosis . It may protect the cell against ion and ph fluctuation.

14. CELL WALL A typical bacterial cell possesses a rigid structure called cell wall that lies outside the plasma membrane It is about 10 -25 nm thick and accounts for about 20 -30% of the dry weight of the cell It is responsible for maintaining the shape of the bacterium and prevents the cell from osmotic lysise The chemical subsatance that comfers rigidity to the cell wall is peptidoglycon. it is a strong polymer found only in prokaryotes. peptidoglycon is a polymer of N-acetyl glucosomine and N- acetyle muramic acid .

15. Bacteria are classified into gram positive and gram negative depending on the nature of the cell wall Gram’s positive bacteria will have thick peptidoglycon layer where as gram negative bacteria are having thin peptidoglycon layer. Gram positive bacteria also contains teichoic acid which is absent in gram negative bacteria.

16. Gram negative bacteria contain an outer membrane that surrounds the peptidoglycon layer which is made up of lipopoly saccharides . The important function of this outer membrane is to serve as protective barrier and prevents or slows the entry of toxic substance that might kill or injure the bacteria. In addition this membrane is anchored to the peptidoglucon by Braun’s lipoprotein.

17. PLASMA MEMBRANE The contents of the bacterial cell with in the boundries of the cell wall form the protoplast. It consists of outer plasma membrane, cytoplasm , and nucleoids . The plasma membrane of bacterial cell is similar to that of eukaryotic cell. The most widely accepted current model for membrane structure is the fluid mosaic model of Singer and Nicolson. According this membrane structurally is a lipid bilayer consisting of two types of proteins peripheral proteins are loosely connected to the membrane and can be easily removed and make 20-30% of the total membrane proteins. about 70-80% of the membrane protein are integral proteins , they are not easily extracted from membrane

18. Functions of plasma membrane Organic and inorganic nutrients are transported through plasma membrane. Consists of enzymes of biosynthetic pathways. The inner membrane invaginates to form mesosomes . It has selective permiability .

19. PILI or FIMBRIAE Many gram positive bacteria have short five hairy appendages that are thinner than flagella and not involved in motility, they are usually called fimbriae Although a cell may be covered by 1000’s of fimbriae , they are visible only under electron microscope due to their small size. They seem to be slendour tubes composed of helically arranged proteins subunits and are about 3-10nm in diameter and upto several micrometer long. Atleast some types of fimbriae attach bacteria to solid surfaces such as rocks in streams and host tissue.

20. Flagella About half of all known bacteria are motile, most use flagella. Long, thin, helical appendages. A bacterium may have one or several flagella, which can be in the following arrangements: Monotrichous : Single polar flagellum at one end. Amphitrichous : Two polar flagella, one at each end. Lophotrichous : Two or more flagella at one or both ends. Peritrichous : Many flagella over entire cell surface.

21. Monotrichous ; Lophotrichous Amphitrichous Peritrichous

22. Flagella have three basic parts 1. Filament: Outermost region. Contains globular protein flagellin . Not covered by a sheath like eucaryotic filaments. 2. Hook: Wider segment that anchors filament to basal body. 3. Basal Body: Complex structure with a central rod surrounded by a set of rings. Gram negative bacteria have 2 pairs of rings. Gram positive bacteria only have one pair of rings.

23. Cytoskeleton These are Filaments & fibers Made of 3 fiber types Microfilaments Microtubules Intermediate filaments 3 functions: mechanical support anchor organelles help move substances

24. VIRUSES WHAT ARE VIRUSES???? Viruses are considered to be the smallest ‘living units’. Viruses may be defined as acellular , Sub microscopic entity consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the host cells using host metabolic machinery. Exsists in both living and non-living form.

25. Morphology of viruses Shape Morphology of viruses Shape Viruses has different shapes such as Spheroid (adenovirus) Elongated (potato viruses) Coiled (beet yellow virus) Bullet shaped (rabies virus) Filamentous ( bacteriophage )

26. Typical structure of virus

27. Capsid Protein coat surrounding nucleic acid Composed of capsomeres The arrangement is characteristic for a particular virus Single protein type Several protein types

28. Envelope Covers capsid in some viruses Combination of Lipids Proteins Carbohydrates It is about 10-15µm thick Can be derived from host cells plasma membrane Spikes Carbohydrate – protein complexes Project from envelope Attachment mechanism Means of identification Hemagglutination Clumping of RBC’s

29. Based on symmetry of capsule or shape Polyhedral viruses Helical viruses Complex viruses Based on presence or absence of envelop Naked capsid viruses Enveloped viruses

30. Polyhedral Capsids are many sided They are of 3 types Terahedral – 4 sides Octahedral – 8 sides Icosahedral – 20 triangular faces and 12 corners In icosahedral capsids are made of many subunits called capsomeres . Ex: adenovirus, herpes virus, etc.

31. Helical Capsid and nucleic acid are helically coiled. Ex: TMV, mumps viurs , influenza virus, Rabies, Ebola, etc

32. Complex Capsid is attached with additional structures Ex: vaccinia virus, phages of T-even series Bacteriophages - Capsid is polyhedral in shape where as sheath is helical

33. Conclusion

34. Reference Dr.R.C Dubey and Dr.D.K Maheshwari . A text book of microbiology. https://scholar.google.co.in/scholar?q=architecture+of+microbial+cell https://www.google.co.in/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=characteristics+of+anaerobes

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