The polysaccharide chains constitute the O-antigens of the Gram-negative bacteria, and the individual monosaccharide constituents confer serologic specificity on these components. Ribosomes - Ribosomes are microscopic "factories" found in all cells, including bacteria. General sequence of steps in the Gram stain procedure and the resultant staining of Gram-positive and Gram-negative bacteria.
Many Gram-positive bacterial membranes contain membrane-bound lipoteichoic acid, and species lacking this component such as Micrococcus and Sarcina spp. In addition to causing endotoxic shock, LPS is pyrogenic, can activate macrophages and complement, is mitogenic for B lymphocytes, induces interferon production, causes tissue necrosis and tumor regression, and has adjuvant properties.
Basal body, the motor portion of the flagellum is the most complex part of a flagellum Fig. A spore coat of keratinlike protein encases the spore contained within a membrane the exosporium. Instead, the chromosome and perhaps ribosomes are the only easily observable intracellular structures found in all bacteria.
Magnetosome Magnetosomes are bacterial microcompartments found in magnetotactic bacteria that allow them to sense and align themselves along a magnetic field magnetotaxis. Although this is only about 0. An extreme excess of carbohydrate causes a significant change in the internal pressure of the cell, which causes the gas vesicles to buckle and collapse and the cell to sink out.
Genetic studies have revealed the existence of mutants with altered biochemical pathways for flagellar motility and chemotaxis. It consists of a rod and one or two pairs of discs. This motility is called twitching motility, which is a type of movement on solid surfaces where rapid and reversible extension and retraction of the fimbriae allow the bacterial cell to crawl along the surface.
Bacterial cells possess various structures external to the cell wall that basically contribute in protection attachment to objects, and cell movement. Gliding bacteria often produce slime, which presumably aids in their motility.
Widely distributed in nature, this enzyme is present in human tissues and secretions and can cause complete digestion of the peptidoglycan walls of sensitive organisms. Clockwise rotation of the flagella disrupts the bundle and the cell tumbles. The cytoplasm is mostly water, but within it are the bacterial inclusions - nucleoid, plasmids, ribosomes and storage granules - as well as the components necessary for bacterial metabolism.
A specialized pilus, the sex pilus, allows the transfer of plasmid DNA from one bacterial cell to another. Capsules and Loose Slime Some bacteria form capsules, which constitute the outermost layer of the bacterial cell and surround it with a relatively thick layer of viscous gel. Teichoic Acids Wall teichoic acids are found only in certain Gram-positive bacteria such as staphylococci, streptococci, lactobacilli, and Bacillus spp.
Deep lakes that experience winter mixing expose the cells to the hydrostatic pressure generated by the full water column.
The morphology of magnetosomes is species-specific. The movement of the basal body is driven by a proton motive force rather than by ATP directly.
Flagella are whip-like structures protruding from the bacterial cell wall and are responsible for bacterial motility i. Since the outer polysaccharide layers of capsule are hygroscopic and bind a significant account of water, it is considered that these layers contribute some role in resistance to desiccation.
Inside the cell wall or rigid peptidoglycan layer is the plasma cytoplasmic membrane; this is usually closely apposed to the wall layer.
Plasmids are small circular DNA fragments found in the cytoplasm that contain code responsible for antibiotic resistance and other characteristics. Different species produce gas vesicle of different diameter, allowing them to colonise different depths of the water column fast growing, highly competitive species with wide gas vesicles in the top most layers; slow growing, dark-adapted, species with strong narrow gas vesicles in the deeper layers.
There do exist, however, specialized groups of bacteria that contain more complex intracellular structures, some of which are discussed below.Todar's Online Textbook of Bacteriology contains 46 chapters on bacteria including structure-function, growth, metabolism, interactions with humans, pathogenesis and medically-important species.
Structure and Function of Bacterial Cells (page 1) (This chapter has 10 pages) Cell wall: Gram-positive bacteria. In this article we will discuss about the cell structure of bacteria with the help of diagrams. A bacterial cell (Fig. ) shows a typical prokaryotic structure.
In bacteria, the cell wall forms a rigid structure of uniform thickness around the cell and is responsible for the characteristic shape of the cell (rod, coccus, or spiral). Inside the cell wall (or rigid peptidoglycan layer) is the plasma (cytoplasmic) membrane; this is usually closely apposed to the wall layer.
Cell Wall: Composed of peptidoglycan (polysaccharides + protein), the cell wall maintains the overall shape of a bacterial cell. The three primary shapes in bacteria are coccus (spherical), bacillus (rod-shaped) and spirillum (spiral).
The enzyme lysozyme, found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.
The gram-positive cell wall Animated guide to bacterial cell structure. Furthermore, gram-negative and gram-positive bacteria differ, particularly, with respect to their cell walls. Despite these variations, however, the bacterial cells are consistent in their fundamental structure and most important constituents.Download