Bacterial cell structure and functions.pptx

Bacterial cell structures and functions for students of microbiology, pathology
Mbbs and doctor of pharmacy students.

1. Bacterial cell structure and functions Dr. Rabia Sadaf Assistant Professor Pathology

2. My students will be able to identify shapes of bacteria. They can describe different parts of bacterial cell and their functions. They can also understand the differences between gram positive and gram negative bacterial cell wall. Learning Objectives

3. Bacteria have characteristic shapes . Can be classified into these basic groups: Cocci (spherical) Bacilli (rod shaped) Spirochetes (spiral) Vibrio (coma shaped) Morphology of Bacteria

4. Morphology of Bacteria

5. Morphology of Bacteria Different sizes of bacilli

6. Morphology of Bacteria

7. Bacterial cell structure

8. Bacterial structure

9. Nucleoid: The bacterial nucleoid contains a single double-stranded deoxyribonucleic acid ( DNA) Only containing a single chromosome. Having no nuclear membrane. Having no nucleolus . Replicating by growth and simple fission, and not by mitosis . Bacterial structure

10. Cytoplasm: The cytoplasm of bacterial cell is a viscous watery solution, or soft gel, containing a variety of organic and inorganic solutes, and numerous ribosomes . Inclusion granules are observed in the cytoplasm in many species of bacteria. Containing plasmids in some species of bacteria. Not containing endoplasmic reticulum and mitochondria . Bacterial structure(contd..)

11. Bacterial ribosomes : They are the site of protein synthesis as in eukaryotic cells, but they differ from eukaryotic ribosomes in size and chemical composition . Bacterial ribosomes are 70S in size, with 50S and 30S subunits. Bacterial structure(contd..)

12. Bacterial structure(contd..) Plasmids: They are extrachromosomal, double-stranded, circular DNA molecules that are capable of replicating independently of the bacterial chromosome . Two types, Transmissible Non Transmissible

13. Functions of plasmids : Plasmids carry the genes for the following functions and structures of medical importance. Antibiotic resistance Resistance to heavy metals, such as mercury and silver Resistance to ultraviolet light, which is mediated by DNA repair enzymes. Pili (fimbriae ) Exotoxins , including several enterotoxins Bacterial structure(contd..)

14. Bacterial structure(contd..) Cytoplasmic membrane: Just inside the cell wall lies the cytoplasmic membrane, which is composed of a phospholipid bilayer similar in microscopic appearance to that in eukaryotic cells.

15. Functions of cell membrane: Active transport of molecules into the cell Energy generation by oxidative phosphorylation Synthesis of precursors of the cell wall Secretion of enzymes and toxins Bacterial structure(contd..)

16. Cell wall : The cell wall is the layer, usually fairly rigid, that lies just outside the cell membrane. It gives shape to the cell and protect it from osmotic lysis. The cell walls of many pathogens have components that contribute to their pathogenicity . The wall can protect a cell from toxic substances and is the site of action of several antibiotics. Peptidoglycan is the most important molecule in the cell walls of bacteria Bacterial structure(contd..)

17. Bacterial structure(contd..)

18. What is Peptidoglycan Peptidoglycan is a complex, interwoven network that surrounds the entire cell It is a complex polymer consisting of three parts: a backbone, composed of alternating N- acetylglucosamine and N- acetylmuramic acid; and a set of identical tetrapeptide side chains attached to N- acetylmuramic acid; and a set of identical peptide cross bridges. Bacterial structure(contd..)

19. Bacterial structure(contd..)

20. Cell walls of Gram positive and Gram negative bacteria  In gram-positive bacteria, there are as many as 40 sheets of peptidoglycan, comprising up to 50% of the cell wall material. I n gram-negative bacteria, there appears to be only one or two sheets, comprising 5~10% of the wall material. Bacterial structure(contd..)

21. Bacterial structure(contd..)

22. Special components of Gram-Positive Cell Walls: Teichoic Acids : These are water soluble polymers. Two types of teichoic acids: wall teichoic acid (WTA), covalently linked to peptidoglycan, and membrane teichoic acid, covalently linked to membrane glycolipids are called lipoteichoic acids (LTA) . The medical importance of teichoic acids Induce septic shock when caused by certain gram positive bacteria Teichoic acids also mediate the attachment of staphylococci to mucosal cells. Bacterial structure(contd..)

23. Special components of Gram-negative Cell Walls An outer membrane containing lipopolysaccharide (Lipid A + polysaccharide)which is an endotoxin and responsible for endotoxic shock A periplasmic space where β-lactamases are found Peptidoglycan layer is very thin Bacterial structure(contd..)

24. Structures outside the cell wall Capsule Flagella Pili (Fimbriae) Glycocalyx (slime layer) Bacterial structure(contd..)

25. Capsule : -Many bacteria are surrounded by a discrete covering layer of a relatively firm gelatinous material composed of polysaccharide that lies outside and immediately in contact with the cell wall . Functions: Determinant of virulence Identification of an organism Capsular polysaccharides are used as the antigens in certain vaccines Adherence of bacteria to human tissues Bacterial structure(contd..)

26. Flagella: Flagella are long, whip like appendages that help in the movement of bacteria. They are composed of many subunits of protein flagellin . Medical Importance: Flagella may play a role in pathogenesis by propelling the bacteria towards the site of infection e.g. E. coli and Proteus species (common pathogens of UTI). Identification of bacteria e.g. Salmonella species Bacterial structure(contd..)

27. Monotrichous Single polar flagellum Lophotrichous multiple polar flagella Peritrichous flagella distributed over the entire cell Bacterial structure(contd..)

28. Pili (Fimbriae): Many gram-negative bacteria possess rigid surface appendages called pili (L "hairs") or fimbriae (L "fringes"). They are shorter and finer than flagella ; they are composed of structural protein subunits termed pilins . Two types Ordinary pili (used for attachment) Sex pili  (forms the attachment between the male (donor) and the female (recipient) bacteria during conjugation) . Bacterial structure(contd..)

29. Bacterial structure(contd..)

30. Bacterial structure(contd..)