Ultrastructure of Bacteria BY: FATIMA KHAN 1ST SEMESTER ROLL NO :22 DEPT. OF BIOTECHNOLOGY PATNA WOMEN’S COLLEGE Introduction of Bacterial cells . Bacteria are unicellular organisms belonging to the prokaryotic group where the organisms lack a few organelles and a true nucleus. Bacteria are microscopic, single-celled organisms that exist in their millions, in every environment, both inside and outside other organisms. Some bacteria are harmful, but most serve a useful purpose. They support many forms of life, both plant and animal, and they are used in industrial and medicinal processes. Ultra structure of Bacteria EXTERNAL STRUCTURES Pili / Fimbriae ⚫ Numerous, short, thin,proteinaceous fibers which protrude from the surface. ⚫ Allow cells to attach to surfaces or other cells. ⚫ Besides the attachment pili, some species produce conjugation pili that establish contact between appropriate cells facilitating transfer of genetic material. Flagella ⚫ Long,hair-like appendage composed of protein and responsible for locomotion ⚫ Each flagellum is composed of a helical filament, hook and basal body. ⚫ The hollow helical filament is composed of long, rigid strands of protein, while the hook attaches the filament to a basal body anchored in the cell membrane Bacterial types based on number and arrangement of flagella Type Characteristic Monotrichous Lophotrichous Amphitrichous A single polar flagellum eg: Vibrio cholerae A cluster of polar flagella eg: Spirillum Flagella at both the ends either singly or in cluster Eg: Aquaspirillum Two or more flagella at one end of bacterial cell eg: Pseudomonas Cell surface evenly surrounded by several lateral flagella eg: E.coli Cells devoid of flagella eg: Lactobacillus Cephalotrichous Peritrichous Atrichous e Glycocalyx ⚫ A viscous polysaccharide material covering the bacterial cells to assist in attachment to a surface and impart resistance to desiccation. ⚫ The layer can be thick and covalently bound to the cell in which case it is known as capsule. ⚫ Thinner, diffuse polysaccharides are referred to as slime layer. Bacterial Cell W all ⚫ Bacterial cell wall is made up of peptidoglycan ⚫ Peptidoglycan consists of chains of disaccharides (glycan strands) cross-linked by peptide bridges. ⚫ Each disaccharide (also called murein), is composed of two monosaccharides, N - acetyl glucosam ine (N A G) and N - acetyl muramic acid (NAM). Structure of Cell wall Cell membrane ⚫ 5 nm thick ⚫ 40% phospholipid and 60% protein ⚫ Fluid in nature and the dynamic model of membrane structure is called the fluid mosaic model. ⚫ i.e.,cell membrane consists of a phospholipid bilayer in which are embedded integral membrane proteins. Cytoplasm ⚫ Cell membrane encloses the cytoplasm. ⚫ It is the compartment within which most growth and metabolism occur. ⚫ Cytoplasm consists of the cytosol, a semifluid mass of proteins, aminoacids, sugars, nucleotides, salts, vitamins and ions all dissolved in water . ⚫ several bacterial sub structures, each with a specific function. Nucleoid ⚫ The chromosome region in a prokaryotic cell appears as a diffuse mass termed the nucleoid. ⚫ The nucleoid does not contain a covering membrane. ⚫ It represents a central subcompartment in the cytoplasm ⚫ Usually there is a single chromosome per cell ⚫ The nucleoid contains the cell’s essential genetic information. ⚫ Most cells have one copy of each gene,and hence the cells are genetically haploid. D Plasmid ⚫ Besides a nucleoid, many prokaryotic cells also contain smaller molecules of circular D N A called plasmids. ⚫ Plasmids contain nonessential genetic information. ⚫ These are extrachromosomal D N A molecule and have about a tenth the size of a prokaryotic chromosome. ⚫ These stable D N A molecules exist as closed loops containing 5 to 100 genes. ⚫ There can be one or more plasmids in a cell and these may contain similar or different genes. Chemical Composition Function External Structures Pili Protein Attachment to surfaces Genetic Transfer Flagella Protein Motility Glycocalyx Polysaccharides Buffer to environment Attachment to surfaces Structure Cell Envelope Cell Wall Gram positives: thick peptidoglycan + teichoic acid Cell protection Shape determination Prevents cell lysis Gram negatives: little peptidoglycan and an outer membrane Cell Membrane Protein Phospholipid Cell Boundary Transport into / out of cell Site of enzymatic reactions e Chemical Composition Function DNA Site of essential genes DNA Site of non essential Ribosomes RNA and Protein genes Protein synthesis Inclusion Glycogen, sulfur, Nutrient storage bodies lipid Polyphosphate Granules Protein shells Storage for ATP and nucleic acids Buoyancy Structure Internal Structures Nucleoid Plasmids Gas vesicles