Bacterial cell structure & classification DR C P PRINCE
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Any bacterial cell whether it is a coccus or a bacillus will have some structures common. These structures are cell wall, cell membrane, cytoplasm, ribosomes and the chromosome. Other intra-cellular structures such as plasmid, inclusion bodies and extra-cellular structures such as capsule, fimbriae and flagella are possessed only by some bacteria.
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Bacterial cell structure & classification DR C P PRINCE
- 1. DR. PRINCE C P HOD & ASSOCIATE PROFESSOR DEPARTMENT OF MICROBIOLOGY Mother Theresa PG&RI of Health Sciences ( Govt of Puducherry Institution) Pondicherry Bacterial Cell
- 2. Bacteria - classification • Based on morphology bacteria are classified into • Cocci(round / spherical shape), • Bacilli(rod shape), • Vibrio(comma shape), • Spirillum(spiral shape), • Spirochaetes(thin spiral), • Actinomycetes( filamentous/branched), • Mycoplasma( cell wall absent-no proper shape), • Chlamydia(virus like intracellular bacteria) • Rickettsia( small cocco bacilli).
- 6. ANATOMY OF BACTERIA CELL • Any bacterial cell whether it is a coccus or a bacillus will have some structures common. These structures are cell wall, cell membrane, cytoplasm, ribosomes and the chromosome. • Other intra-cellular structures such as plasmid, inclusion bodies and extra-cellular structures such as capsule, fimbriae and flagella are possessed only by some bacteria.
- 7. Bacteria- Prokaryotic cell • 1. No “true” nucleus - nucleoid. a. No nuclear membrane. b. No paired chromosomes. c. No histones. d. No nucleolus. • 2. No cell organelles. • 3. No cytoplasmic streaming. • 4. Cell membrane contains no sterols. • 6. Division - binary fission.
- 8. Parts of Bacterial cell • Cell wall: made up of Peptidoglycan (mucopolysaccharide), responsible for shape and protection. • Cell membrane: semi permeable membrane limiting the cytoplasm • Flagellum: Locomotory structure for motility. Different types of arrangement seen in different bacteria. Monotrichous, Lophotrichous ,Amphitrichous,Peritrichous etc. • Fimbriae/Pili: structure used for attachment • Capsule: outer mucous covering present in some bacteria • Chromosome(DNA): single ,circular DNA • Plasmid: extra chromosomal genes in cytoplasm • Endospore: structure produced by some bacteria during unfavorable condition • Ribosome: 70S ribosome for protein synthesis • Mesosomes: analogous structure to Mitochondria for ATP synthesis
- 10. 10 Eukaryotic cell Prokaryotic cell Gram + Gram - Cell wall Rough endoplasmic reticulum Mitochondria (e.g. animal) Nucleoid Nucleus Cell membrane Cytoplasm Flagellum Cell (inner) membrane Outer membrane Ribosomes Granule Cell wall Capsule Pili
- 11. Nucleoid - Chromosome – DNA • 1. Single, circular structure (haploid genome) • 2. < eukaryotic chromosomes, ~ 3,500 genes • 3. Not in nucleus - no nuclear membrane. • 4. Supercoiling - DNA gyrase - DNA replication
- 12. Cytoplasmic/Inner Membrane 1. similar to eukaryotic plasma membrane and mitochondrial membrane 2. little usefulness as target for antibiotics 3. carries out many functions a. transport: facilitated diffusion, active transport, group translocation (phosphotransferase – carbos) b. electron transport and oxidative phosphorylation c. energy production d. motility e. replication
- 13. Cell wall/ cell envelope (Peptidoglycan = murein layer) • 1. unique to prokaryotes a. Antimicrobials: β-lactams: penicillins and cephalosporins, vancomycin, bacitracin b. enzyme lysozyme hydrolyses backbone • 2. composition - murein backbone with unusual peptide chain a. N-acetyl glucosamine - N-acetyl muramic acid b. pentapeptide with L and D amino acids
- 15. GRAM POSITIVE CELL ENVELOPE 15 Cytoplasm Lipoteichoic acid Peptidoglycan-teichoic acid Cytoplasmic membrane Degradative enzyme
- 16. GRAM NEGATIVE CELL ENVELOPE 16 Cytoplasm Inner (cytoplasmic) membrane Outer Membrane (Major permeability barrier) Lipopolysaccharide Porin Braun lipoprotein Degradative enzyme Periplasmic binding protein Permease
- 17. Lipo polysaccharide (LPS) – Endotoxin The most important part of gram-negative bacteria a. lipid A i. embedded in membrane = endotoxin activity ii. unique C14 fatty acid - β-hydroxy myristic acid, phosphates, glucosamine b. core oligosaccharide i. highly conserved among different bacteria ii. unique components - KDO and heptose
- 19. Peptidoglycan 19 • single macromolecule • highly cross-linked • surrounds cell • provides rigidity
- 20. Peptidoglycan • glycan backbone – muramic acid – glucosamine • peptide side chain • peptide cross-bridge – D- and L- amino acids – diaminopimelic acid 20
- 21. 21 Muramic acid, D-amino acids diaminopimelic acid not synthesized by mammals
- 22. Peptidoglycan 22 Muramic acid Glucosamine L-alanine D-glutamic acid L-lysine/Diaminopimelic acid D-alanine D-alanine
- 23. Mesosomes • Mesosomes are the invaginated structures formed by the localized infoldings of the plasma membrane. The invaginated structures comprise of vesicles, tubules of lamellar whorls . • perform functions like cellular respiration( analogues to mitochondria) • Generally mesosomes are found in association with nuclear area or near the site of cell division. • They are absent in eukaryotes.
- 24. Ribosomes 1. 70S ribosomes composed of 50S and 30S subunits 2. co-transcription-translation 3. target of many useful antimicrobials: aminoglycosides tetracyclines chloramphenicol macrolides - erythromycin
- 25. 25 • Flagella – embedded in cell membrane – project as strand – Flagellin (protein) subunits – move cell by propeller like action
- 26. Axial filaments –spirochetes –similar function to flagella –run lengthwise along cell –snake-like movement 26
- 27. 27 Pili (fimbriae) • hair-like projections of the cell • sexual conjugation • adhesion to host epithelium
- 28. 28 Capsules and slime layers • outside cell envelope • well defined: capsule • not defined: slime layer or glycocalyx • usually polysaccharide • often lost during in vitro culture • protective in vivo
- 29. Endospores (spores) 29 • Dormant cell • Produced when starved • Resistant to adverse conditions - high temperatures - organic solvents • contain calcium dipicolinate • Bacillus and Clostridium
- 32. Spores a. certain gram-positives only - both aerobic and anaerobic b. metabolically inactive c. resistant to heat (boiling), desiccation ►need autoclave (121˚C, 15 min) d. Contain dipicolinic acid e. developmental stage in response to stress: stress sporulation vegetative (growing) cell dormant spore germination
- 34. Plasmids 34 • Extra-chromosomal DNA • multiple copy number • coding - pathogenesis factors - antibiotic resistance factors • bacterial replication
- 39. Thanks 39