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NAJRAN UNIVERSITY College of Medicine

NAJRAN UNIVERSITY College of Medicine. Microbiology &Immunology Course Lecture No. 3. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. The Nuclear Body ‑ Bacteria have a primitive nucleus (prokaryotic), which has no nuclear membrane and does not contain nucleoli.

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NAJRAN UNIVERSITY College of Medicine

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  1. NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 3 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. The Nuclear Body ‑ Bacteria have a primitive nucleus (prokaryotic), which has no nuclear membrane and does not contain nucleoli. ‑ The bacterial chromosome is a single circular double‑stranded DNA molecule, which carries the genetic material (determinants) that control the bacterial properties and behaviour. ‑ The chromosome is duplicated prior to cell division and each daughter cell will contain an identical copy of the chromosome.

  3. Flagellae ‑ These are long relatively thick filamentous appendages extended outside the cell ‑ They are the organs of bacterial cell motility. ‑ Protein in nature (composed of flagellin). ‑ Antigenic (carry flagellar or "H" antigen).

  4. Fimbriae (Pili) • -Filamentous appendages that are shorter, thinner and more numerous than flagellae. • -Protein in nature (composed of pilin). • -Antigenic (carry fimbrial or F antigens). • -Functionally of two types. • Common pili(fimbriae) are organ of attachment or adhesion. • Sex pili(F pili) through which genetic material (e.g. plasmids) are transferred from donor (male or F+) cells to recipient (female or F‑) cells.

  5. Capsule • -Is the outermost layer in capsulated bacteria (outside cell wall). • -A viscous material with well‑defined border • -Antigenic (capsular or K antigen) • -They are important virulence factors that protect bacteria against phagocytosis by the host phagocytic cells.

  6. Spores • -Some bacteria are spore‑forming and can develop spores upon exposure to adverse environmental conditions (e.g. heat, dryness, poor nutrition, etc.) • -Steps: • Spore core: By ingrowth of the cytoplasmic membrane cutting off a portion of the cytoplasm including the nuclear material, ribosomes and little water • Spore cortex:a thick cortex of peptidoglycan • Spore coat: Around the cortex. Responsible for the marked resistance of the spore. This resistance is also mediated by calcium • - Once the hazard is removed, the spore germinates to create a new population (Germination)

  7. Bacterial reproduction • -Being a prokaryote, bacteria multiply by simple binary fission. • -The chromosome duplicates itself and each copy is attached to the cytoplasmic membrane at the mesosome. • -The cytoplasmic membrane forms a new transverse mmembrane between the sites of attachment of the two daughter chromosomes. This transverse membrane grows inward. • -A new transverse cell wall is formed and grows inward. • -A complete transverse septum is formed and two daughter cells are generated which may separate or remain attached resulting in formation of cell groupings (e.g. clusters or chains).

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