Structural Features of
Prokaryotic Cells continued
• B. Anatomy of Prokaryotic Cells
Bacterial shapes and configuration
Cell membrane
Cell Wall
• Gram - positive
• Gram – negative
Outline
Structural Features of
Prokaryotic Cells.
• C. Structures External to the Cell Wall.
– Glycocalyx (EPS)
– Flagella
– Fimbriae and Pili
• D. Inside Cell Membrane
– Cytoplasm ( Ribosomes,inclusions, gas vesicles) – Nucleoid
– Spores
Gram negative Gram positive Fig. 4.14
Prokaryotic cell
Fig. 4.6
Glycocalyx
• Sugar coat - polysaccharide, external to outer cell surface
• Synthesized inside the cell and transported to the cell's surface.
• If it remains attached to surface called capsule or extracellular polysaccharide (EPS)
• If only loosely attached called slime layer.
Bacterial Glycocalyx
Fig. 4.12
Glycocalyx
• Functions:
– It prevents dehydration polysaccharides adsorb water
– It protects the cell. (virulence factor)
• In pathogenic bacteria we find that it inhibits phagocytosis by host cells.
– It helps bacteria adhere to surfaces.
• Streptococcus mutants (cause of dental caries) initially binds to teeth by its glycocalyx ( EPS).
Flagella
• Long filamentous appendages that propels bacteria.
• Motile bacteria use flagella
( singular - flagellum) to move
• Bacterial flagella are rigid, helical protein filaments that are attached to the cell
• Filaments composed of multiple subunits of a protein called flagellin.
• Flagellin aggregates to forms a helix around a hollow core. Flagella continued
• Arrangements
– monotrichous - single polar flagellum
– lophotrichous - two or more flagella at one pole of cell
– amphitrichous - a tuft of flagella at each end of cell – peritrichous - flagella distributed over the entire cell
Salmonella with flagella
Attachment of the Flagella
• Flagellum has three major sections:
• filament - which extends into the environment
• a hook - curved section connecting filament to the cell surface
• basal body - anchors the flagellum to the cell wall and membrane by means of disc shaped protein rings. Bacterial Flagella Structure
Movement
• The basal body acts as a motor and spins the flagellum around.
• Movement in clockwise direction causes the cells to tumble. • Movement in a counterclockwise direction, moves the cell in a single direction, called a run. Chemotaxis and Phototaxis
• Movement of bacteria toward (an attractant) or away from (a repellent) is called taxis
• chemotaxis
– Movement of cells either toward or away from a concentration of a substance in their environment.
• phototaxis
– Movement of cells either toward or away from a source of light.
Chemotaxis in Bacteria
Flagella’s Medical Significance
• H antigens
– H antigens are antibodies against flagella proteins.
• Used to distinguish variation within a species of Gram-negative bacteria.
– There are 50 different H antigens for
E. coli
– Pathogen E. coli O157:H7
– H refers to H-antigen 7.
Axial filaments
• Spirochetes have an axial filament or endoflagella. • Spirals beneath an outer sheath the wraps around the cell.
– Like flagella when rotated cause bacteria to spiral like a corkscrew through its environment. Fimbriae and Pili
• Thin fibrillar appendages commonly found on Gram negative bacteria
– (often the two terms are used interchangeable) • They are smaller than flagella
• fimbriae usually refers to filaments responsible for attachment to surfaces
(proteins that ties bacteria down)
• pili usually refer to filaments that are used to mediate the attachment to other bacteria in preparation for the transfer of
DNA from one cell to another.
Structural Features of
Prokaryotic Cells.
• C. Structures External to the Cell Wall.
Glycocalyx (EPS)
Flagella
Fimbriae and Pili
• D. Inside Cell Membrane
– Cytoplasm ( Ribosomes,inclusions, gas vesicles) – Nucleoid
– Spores
Inside the Prokaryotic
Plasma Membrane
• Cytoplasm
• 80% water but has a gel-like consistency
• Contains proteins
