Bacterial Cell Structure by Dr. Shireen Rafiq
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Bacterial Cell Structure by Dr. Shireen Rafiq
- 1. Bacterial Cell Structure Dr Shireen Rafiq MBBS, M.Phil, Ph.D
- 2. 2 Microbiology • Agents of human infection: – Bacteria Prokaryotes – Helminths Eukaryotes – Protozoa Eukaryotes – Fungi Eukaryotes – Viruses Noncellular
- 3. • Difference between Eukaryotes and Prokaryotes • Structure • Replication • Nucleic acid
- 4. 4 Earliest Prokaryotes • Most numerous organisms on Earth • Include all bacteria • Earliest fossils date 2.5 billion years old
- 5. BACTERIA • Bacteria are large group of single celled prokaryotic microorganisms • 10 times as many bacteria cells in the human flora as there are human cell in the body
- 6. Shape of Bacteria • Three basic shapes • Cocci:streptococci, Staphylococci, Diplococci • Bacilli: E.coli, Klebsiella, Bacillus. • Spirochetes: Treponema, Borrelia
- 8. Bacterial Size • Bacteria range in size from about 0.2 to 5 µm. • The smallest bacteria (Mycoplasma) are about the same size as the largest viruses (poxviruses) and are the smallest organisms capable of existing outside the host. • The longest bacteria rods approach the size of some yeasts and human R.B.Cs
- 9. 9
- 10. According to staining • Gram positive Thick peptidoglycan layer and teichoic acid • Gram negative Thin peptidoglycan layer and lipopolysaccharide- endotoxin • Acid fast bacilli Mycolic acid (lipids)
- 11. • Some bacteria are variable in shape • PLEOMORPHIC----many shaped • Shape of the bacteria is determined by its rigid cell wall • The microscopic appearance of bacterium is most important criteria for its identification
- 12. 12 pH requirements • Most grow best at pH of 6.5 to 7.0 • Many act as decomposers recycling nutrients • Some cause disease (Pathogenic)
- 13. The Prokaryote • Structural Components MACROMOLECULE SUBUNIT POSITION IN CELL PROTEIN Amino Acid Flagella, pili, cell wall, cytoplasmic membrane, ribosomes, cytoplasm POLYSACCHARIDE Sugar/Carbohydrate Capsule, Inclusions, Cell wall PHOPHOLIPID Fatty Acid Membranes NUCLEIC ACID (DNA/RNA) Nucleotide DNA, Nucleoid, Plasmids, Ribosomes,
- 14. Structural Components Prokaryotes have 5 essential components • Nucleoid (DNA) • Ribosomes • Cell membrane • Cell wall • Surface layer (Capsule) • Appendages
- 16. BACTERIAL STRUCTURE COVERING LAYERS • Cell wall • Peptidoglycan Sugar back bone with peptide side chains,which are cross linked Rigidity osmotic protection , site of action of antibiotic, lysozyme degrade. Outer membrane Gram Negative bacteria Lipid A Polysaccharide Toxic component of endotoxin. Surface antigen. Surface fiber on Gram Positive bacteria Teichoic acid Surface antigen
- 18. 18 Protection • Cell Wall made of Peptidoglycan • May have a sticky coating called the Capsule for attachment to host or other bacteria
- 19. FUNCTION OF CELL WALL • Maintaining the cell's characteristic shape • Countering the effects of osmotic pressure • Providing attachment sites for bacteriophages-teichoic acids • Providing a rigid platform for surface appendages- flagella, fimbriae
- 20. Peptidoglycan
- 22. COMPARISON Property Gram Positive Gram Negative Thickness of wall 20-80 nm 10 nm Number of layers in wall 1 2 Peptidoglycan content >50% 10-20% Teichoic acid in wall + - Lipid and lipoprotein content 0-3% 58% Protein content 0% 9% Lipopolysaccharide 0 13% Sensitive to penicliiin + - (not as much) Digested by lysozyme + - (not as much)
- 23. Properties of cell wall • Gram negative bacteria contains endotoxin--- lipopolysaccharide • Polysaccharides and proteins are antigens • Porin proteins helps entry of hydrophilic molecules • Teichoic acid are fibers on outer surface of gram positive ---ability to induces septic shock
- 24. Cell Membrane • Composed of phospholipid bilayer • FUNCTIONS • Active transport • Energy generation---oxidative phosphorylation • Synthesis of precursors of cell wall • Secretion of enzymes and toxins
- 25. 25 • Infoldings of cell membrane carry on photosynthesis & cellular respiration • Infoldings called Mesosomes
- 28. Plasmids • Molecules of DNA that are found in bacteria separate from the bacterial chromosome. • A circular molecule only much SMALLER than the genomic DNA • REPLICATE AUTONOMOUSLY from the genomic chromosome. Often there are MANY PLASMID COPIES present in one cell. Further, a cell may contain SEVERAL DIFFERENT PLASMIDS or it may contain NO PLASMIDS at all. Plasmids generally carry genes that are NOT ESSENTIAL for a cell's survival • May carry genes for ANTIBIOTIC RESISTANCE
- 29. Transposons • Transposons are pieces of DNA move from one site to another ---- within or between the DNAs of bacteria plasmid or bacteriophage. • Nick name as Jumping genes • Genes for one or more (usually more) proteins imparting resistance to antibiotics. When such a transposon is incorporated in plasmid, it can leave the host cell and move to another. This is the way that the alarming phenomenon of multidrug antibiotic resistance spreads so rapidly.
- 31. 31 Flagella • Bacteria that are motile have appendages called flagella • Attached by Basal Body • A bacteria can have one or many flagella
- 32. 32 Flagella • Made of Flagellin • Used for Classification • Monotrichous: 1 flagella • Lophotrichous: tuft at one end • Amphitrichous: tuft at both ends • Peritrichous: all around bacteria
- 33. 33 Pili • Short protein appendages PILIN • Smaller than flagella • Adhere bacteria to surfaces • Used in conjugation for Exchange of genetic information • Aid Flotation by increasing buoyancy
- 36. 36 Shapes Are Used to Classify • Bacillus: Rod shaped • Coccus: Spherical (round) • Vibrio: Comma shaped with flagella • Spirillum: Spiral shape • Spirochete: wormlike spiral shape
- 37. 37 Grouping of Bacteria • Diplo- Groups of two • Strepto- chains • Staphylo- Grapelike clusters
- 39. 39
- 40. 40 Bacillus and E. coli
- 41. Spirochetes
- 42. ACCORDING TO STAINING GRAM STAINING
- 44. Crystal violet Gram's iodine Decolorise with acetone Counterstain with e.g. methyl red Gram-positives appear purple Gram-negatives appear pink The Gram Stain
- 45. Gram-positive rods Gram-negative rods Gram-positive cocci Gram-negative cocci
- 49. FORMATION OF BACTERIAL SPORE
- 51. • Found in Gram positive bacteria • Tough, heat resistant • Peptidoglycan > Picolinic acid