Presentation on theme: "Prokaryotic Cells BACTERIA. The Prokaryotic Cell Members of the prokaryotic world make up a vast heterogeneous group of very small single-celled organisms."— Presentation transcript:
Prokaryotic Cells BACTERIA
The Prokaryotic Cell Members of the prokaryotic world make up a vast heterogeneous group of very small single-celled organisms. Include bacteria and archae, although the majority are bacteria The thousands species of bacteria are differentiated by many factors such as: Morphology (shape), chemical composition (often detected by staining reactions), nutritional requirements, biochemical activities, and sources of energy (sunlight or chemicals) These differences can only be seen with the use of a microscope
Size, Shape, and Arrangement Bacteria come in many sizes, and several shapes. Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in length Basic shapes include: Cocci- round shaped Bacillus - rod shaped Spirillum- spiral shaped, helical shape like corkscrew, have rigid bodies, and use flagella to move Vibrio - curved Spirochetes- helical and flexible, move by axial filaments found within flexible external sheath Square Star
Cell Cluster Formation Bacteria are also classified according to cell cluster formation: Streptobacillus Cluster formationDescription Diplococci Two cocci cells paired StaphylococciNumber of cells clustered together ( grape-like ) Streptococci & Streptobacillus Number of cells arranged in a chain
vibriobacillus spirochete coccusspirillumbacillus Learning Check: What Shape are these bacteria?
Shape and Arrangement The shape of bacteria is determined by heredity. Most bacteria are monomorphic : maintain a single shape Environmental factors can alter that shape Some bacteria like Rhizobium and Corynebacterium are pleomorphic : can have many shapes, not just one. Source for figure:
*Cell wall- Most bacteria have a cell wall but there are some that do not like Mycoplasma species Basic Components of Bacteria
Structures External to the Cell Wall Possible structures external to the prokaryotic cell wall are: Glycolax Flagella Axial filaments Fimbrae and Pili
What is the Glycocalyx? Means sugar coat & is the general term used for substances that surround cells Bacterial glycocalyx is a viscous (sticky), gelatinous polymer that is external to the cell wall Composed of a polysaccharide, polypeptide, or both Two types: Capsule: substance is organized and is firmly attached to the cell wall Slime layer: substance is unorganized and only loosely attached to the cell wall glycocalyx Fig. 1 Source for Fig. 1:
(a) Micrograph of Streptococcus pneumoniae, the common cause of pneumonia, showing a prominent capsule. (b) Bacteroides, a common fecal bacterium, has a slime layer surrounding the cell
Learning Check What advantage does a glycocalyx provide a cell? (think about its composition)
Glycocalyx Very important component of biofilms Biofilms are densely packed communities of microbial cells that grow on living or inert surfaces A glycocalyx that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS) EPS protects the cells within it Facilitates communication among them and enables the cells to survive by attaching to various surfaces in their natural environment Source for Fig. 2 Fig. 2
Flagella Some prokaryotes have flagella which are long filamentous appendages that propel bacteria Peritrichous : flagella distributed over the entire cell Polar: at one or both poles or ends of the cell Monotrichous: A single flagellum at one pole Lopothrichous: a tuft of flagella coming from one pole Amphitrichous: flagella at both poles of the cell Bacteria that lack flagella re referred to as atrichous (without projections)
Flagellar Movement Figure 3.9 Motion of a peritrichous bacterium. In peritrichous bacteria, runs occur when all of the ﬂagella rotate counterclockwise and become bundled. Tumbles occur when the ﬂagella rotate clockwise, become unbundled, and the cell spins randomly. In positive chemotaxis (shown), runs last longer than tumbles, resulting in motion toward the chemical attractant.
Axial Filaments Spirochetes have unique structure and motility Move my means of axial filaments Bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell The rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion
Fimbriae and Pili Many gram-negative bacteria contain hair-like appendages that are shorter, straighter, and thinner than flagella are used for attachment and transfer of DNA rather than for motility Fimbrae can occur at the poles of the bacterial cell or entire surface of cell H ave a tendency to adhere to each other and to surfaces Pili are usually longer than fimbrae but shorter than flagella and are found as one or two per cell Involved in motility and DNA transfer
Learning Check Several Escherichia coli cells are connected by conjugation pili. How are pili different from bacterial ﬂagella?