* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download lec1
Survey
Document related concepts
Cell encapsulation wikipedia , lookup
Cell nucleus wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cell culture wikipedia , lookup
Biochemical switches in the cell cycle wikipedia , lookup
Extracellular matrix wikipedia , lookup
Signal transduction wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cell growth wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
Lipopolysaccharide wikipedia , lookup
Cytokinesis wikipedia , lookup
Cell membrane wikipedia , lookup
Transcript
Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri Eukaryotic and Prokaryote cell structure: Prokaryote In comparison to eukaryotes, the intracellular features of the bacterial cell are extremely simplistic(figure1). Bacteria do not contain organelles in the same sense as eukaryotes as shown in table (1). Table (1):Characteristic of Prokaryotic bacterial cell and Eukaryotic cell. characteristic Prokaryotic Eukaryotic cell. bacterial cell. DNA within a nuclear membrane . No yes Mitotic division No yes No yes Chromosome number. one More than one Membrane–bound organelles No yes Size of ribosome. 70s 80s Cell wall containing peptidoglycan. yes No DNA associated with histon Such as mitochondria and lysosomes. Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri Figure (1): Prokaryote cell structure. Cell morphology: Bacteria come in a wide variety of shapes Perhaps the most elemental structural property of bacteria is cell morphology (shape). Typical examples include: coccus (spherical) bacillus (rod-like) spirillum (spiral) filamentous Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri Figure (1) :the bacterial shape. Bacterial cell size: Bacteria range in size fro m about 0.2 to 5 µm the smallest bacteria (mycoplasma)are about the same size as the largest viruses ( poxviruses) and are the smallest organisms capable of existing outside a host .the longest bacteria rods approach the size of some yeasts and human red blood cell. Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri The bacterial structure: bacterial cell wall: The structure of peptidoglycan. As in other organisms, the bacterial cell wall provides structural integrity to the cell. In prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor pressure caused by the much higher concentrations of proteins and other molecules inside the cell compared to its external environment. The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan (poly-N- acetylglucosamine and N-acetylmuramic acid), which is located immediately outside of the cytoplasmic membrane. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. It is relatively porous and is not considered to be a permeability barrier for small substrates. While all bacterial cell walls (with a few exceptions e.g. intracellular parasites such as Mycoplasma) contain peptidoglycan, not all cell walls have the same overall structures. There are two main types of bacterial cell walls, Gram positive and Gram negative, which are differentiated by their Gram staining characteristics. For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan. Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri The Gram positive cell wall is characterized by the presence of a very thick peptidoglycan layer, which is responsible for the retention of the crystal violet dyes during the Gram staining procedure. in the Gram positive cell wall are polyalcohols called teichoic acids, some of which are lipid-linked to form lipoteichoic acids. Because lipoteichoic acids are covalently linked to lipids within the cytoplasmic membrane they are responsible for linking the peptidoglycan to the cytoplasmic membrane. Teichoic acids give the Gram positive cell wall an overall negative charge due to the presence of phosphodiester bonds between teichoic acid monomers. Unlike the Gram positive cell wall, the Gram negative cell wall contains a thin peptidoglycan layer adjacent to the cytoplasmic membrane, which is responsible for the cell wall's inability to retain the crystal violet stain upon decolourisation with ethanol during Gram staining. In addition to the peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by phospholipids and lipopolysaccharides which face into the external environment. As the lipopolysaccharides are highly-charged, the Gram negative cell wall has an overall negative charge. The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains (i.e. sub-species) and is responsible for many of the antigenic properties of these strains. Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri The bacterial cytoplasmic membrane: The bacterial cytoplasmic membrane is composed of a phospholipid bilayer and thus has all of the general functions of a cell membrane such as acting as a permeability barrier for most molecules and serving as the location for the transport of molecules into the cell. In addition to these functions, prokaryotic membranes also function in energy conservation as the location about which a proton motive force is generated. Unlike eukaryotes, bacterial membranes (with some exceptions e.g. Mycoplasma generally do not contain sterols. However, many microbes do contain structurally related compounds called hopanoids which likely fulfill the same function. Unlike eukaryotes, bacteria can have a wide variety of fatty acids within their membranes. Along with typical saturated and unsaturated fatty acids, bacteria can contain fatty acids with additional methyl, hydroxy or even cyclic groups. The relative proportions of these fatty acids can be modulated by the bacterium to maintain the optimum fluidity of the membrane (e.g. following temperature change). As a phospholipid bilayer, the lipid portion of the outer membrane is impermeable to charged molecules. However, channels called porins are present in the outer membrane that allow for passive transport of many ions, sugars and amino acids across the outer membrane. These molecules are therefore Lec:1 Microbiology Ass.lecturer: Israa Al- Yasiri present in the periplasm, the region between the cytoplasmic and outer membranes. The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding or hydrolysis and reception of extracellular signals. The periplasm it is thought to exist as a gel-like state rather than a liquid due to the high concentration of proteins and peptidoglycan found within it. Because of its location between the cytoplasmic and outer membranes, signals received and substrates bound are available to be transported across the cytoplasmic membrane using transport and signalling proteins imbedded there.