Structure of bacteria 1 and gram stainng
- 1. STRUCTURE OF BACTERIA- I By Dr. M. Younus Jamal MBBS, PhD, CHPE Assistant professor Department of Pathology Jinnah Medical & Dental College, Sohail University
- 3. LEARNING OBJECTIVES • Understand the shape & size of bacteria. • Describe the structure of bacterial cell wall. • Know the components of the cytoplasm of bacteria. • Identify the specialized structures outside the cell wall. • Understand the staining patterns.
- 4. INTRODUCTION • Cells fall into one of two broad categories: • Prokaryotic • Eukaryotic. • Single-celled organisms Bacteria and Archaea are classified as prokaryotes • (pro = before; karyon– = nucleus). • Animal cells, plant cells, fungi, and protists are eukaryotes • (eu = true).
- 5. PROKARYOTES • Unicellular organisms that lack membrane-bound structures e.g., nucleus. • Small, simple cells, measuring around 0.1-5 μm in diameter. • DNA bundles together in a region called the nucleoid. • Molecules of protein, DNA and metabolites, float in the cytoplasm. • Prokaryotes can be split into two domains, bacteria and archaea.
- 7. PROKARYOTES – COMPONENTS. • Nucleoid: • Central region of the cell that contains its DNA. • Ribosome: • Ribosomes are responsible for protein synthesis. • Cell wall: • Provides structure and protection from the outside environment. • Most bacteria have rigid cell wall made from carbohydrates & proteins called peptidoglycans. • Cell membrane: • Also known as plasma membrane, separates cell from outside environment. E.g. Mycoplasma species.
- 8. PROKARYOTES – COMPONENTS. • Capsule: • Layer of carbohydrates that surrounds the cell wall. • It helps the bacterium to attach to surfaces. • Fimbriae: • Fimbriae are thin, hair-like structures that help with cellular attachment. • Pili: • Pili are rod-shaped structures involved in multiple roles, including attachment and DNA transfer. • Flagella: • Flagella are thin, tail-like structures that assist in movement.
- 10. Question? • Do prokaryotes have a nucleus? • Answer • Prokaryotes do not have a nucleus. Instead, prokaryote DNA can be found, bundled but free-floating, in a central region called the nucleoid. • Prokaryote DNA is usually found as a single chromosome of circular DNA. These organisms also lack other membrane- bound structures such as the endoplasmic reticulum.
- 15. • What are plasmids? • Answer: • A plasmid is a small circular DNA molecule found in bacteria and some other microscopic organisms. Plasmids are physically separate from chromosomal DNA and replicate independently. • Plasmids are important “vehicles” for the communication of genetic information between bacteria. The exchange of plasmids transmits pathogenically and environmentally relevant traits to the host bacteria, promoting their rapid evolution and adaptation to various environments. The genes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance.
- 16. STAINING
- 17. GRAM STAINING • Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: • Gram-positive bacteria • Gram-negative bacteria. • Danish bacteriologist Hans Christian Gram, developed the technique in 1884.
- 18. GRAM STAINING • Gram positive bacteria: • Retain the crystal violet iodine complex in the presence of lipid solvent acetone alcohol. • Gram negative bacteria have an outer lipid containing membrane & thin peptidoglycan. • Lose the purple dye when treated with acetone alcohol. • They become colorless and then stain pink when exposed to a red dye – safranin.
- 21. microscopic image of a Gram stain of mixed Gram-positive cocci (Staphylococcus aureus, purple) and Gram-negative bacilli
- 23. CLASSIFICATION •Bacteria are classified by shape into: • Cocci (Round) • Bacilli (rods) • Spirochetes (spiral)
- 26. CELL WALL
- 27. STRUCTURE OF BACTERIA – CELL WALL • Outermost component. • They have surface features: • Capsule • Flagella • Pili • Located external to the cytoplasmic membrane. • Composed of peptidoglycan.
- 28. •Electron micrograph of a thin section of Neisseria gonorrhoeae showing the organizational features of prokaryotic cells. •Electron-transparent nuclear region (n) packed with DNA fibrils, the dense distribution of ribosomal particles in the cytoplasm, and the absence of intracellular membranous organelles.
- 29. BACTERIAL CELL WALL • Outermost component. • Common to all bacteria. • Mycoplasma species are bounded by a cell membrane, not a cell wall. • Cell wall also contains surface features external to cell wall. E.g.: • Capsule • Flagella • Pili
- 31. CELL WALL INNER LAYER – PEPTIDOGLYCAN •Found only in bacterial cell wall. •Peptidoglycan provides • Structural support. • Maintains the shape of the cell.
- 32. CELL WALL INNER LAYER – PEPTIDOGLYCAN • The term peptidoglycan is made up of: • Peptides (Peptides are short chains of amino acids linked by peptide bonds). • Sugars (glycan) • Also called murein or mucopeptide. • Complex interwoven network.
- 34. CELL WALL INNER LAYER – PEPTIDOGLYCAN • Composed of a single covalently linked macromolecule. • Peptidoglycan is made up of a polysaccharide backbone. • Consists of alternating: • N-Acetylmuramic acid (NAM) • N-acetylglucosamine (NAG) residues in equal amounts.
- 36. CELL WALLS OF GRAM – POSITIVE & GRAM – NEGATIVE BACTERIA.
- 37. CELL WALLS OF GRAM – POSITIVE & GRAM – NEGATIVE BACTERIA. • Peptidoglycan layer is thicker in gram – positive than in gram – negative. • Gram – positive bacteria have teichoic acid protruding outside from peptidoglycan; gram negative bacteria do not have it. • Gram – negative bacteria have a complex outer layer consists of lipopolysaccharide (LPS), lipoprotein & phospholipid – called envelope. Also acts endotoxin. • Periplasmic membrane space between outer membrane layer and cytoplasmic membrane in gram – negative bacteria.
- 38. CELL WALLS OF GRAM – POSITIVE & GRAM – NEGATIVE BACTERIA. • Both gram – positive and gram – negative bacteria contain polysaccharides and proteins on their surface – antigens.
- 39. CELL WALL- PORINS •Are proteins. •Play a role in passage of small, hydrophilic molecules into cells. •Several types of porins are found. •Found in both gram – negative and positive bacteria. •Porins allow entry of: • Amino acids • Vitamins • Metals • Microbial drugs
- 40. CELL WALLS OF ACID-FAST BACTERIA • Have unusual cell wall. • Resist staining with gram stains. • Due to high concentration of lipids – mycolic acids. • E.g. Mycobacterium Tuberculosis.
- 41. CELL WALL OUTER LAYER – LIPOPOLYSACCHARIDE • Component of cell wall of gram-negative bacteria. • Forms the endotoxin. • Integral part of cell envelope. • Causes disease features like fever and shock. • LPS is composed of 3 units: • A phospholipid called lipid A (responsible for toxic effects) • A core polysaccharide of 5 sugars linked to lipid A through ketodeoxyoctulonate. • Outer polysaccharide consists of 25 repeating units of 3 – 5 sugars. Forms O antigen of gram-negative bacteria.
- 43. STRUCTURE OF BACTERIA – TEICHOIC ACID • Fibers located in the outer layer of the gram-positive cell wall & extend from it. • Composed of polymers of either glycerol phosphate or ribitol phosphate. • Lipoteichoic acid polymers of glycerol teichoic acid penetrating the peptidoglycan layer are linked to lipids of the cytoplasmic membrane. • Induce inflammation and septic shock caused by gram-positive bacteria. • Mediate attachment of staphylococci to mucosal cells. • Not found in gram – negative bacteria.
Editor's Notes
- #12: Kingdom Monera belongs to the prokaryote family. The organisms belonging to this kingdom do not contain a true nucleus. These are the oldest known microorganisms on earth. Their DNA is not enclosed within the nucleus. Autotrophs are organisms that produce their own food whereas heterotrophs are organisms that consume the food produced. Autotrophs are known as producers as they can make their own food from raw materials present, whereas heterotrophs are called consumers as they cannot make their own food.