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1、Chapter 2 Cell Biology2021/3/111 2.1 Overview of the structure of microbial cells 2.2 Procaryotic cell wall 2.3 Cytoplasmic membrane 2.4 Cellular genetic information 2.5 Cytoplasmic matrix Ribosome and Inclusions 2.6 Components external to the cell wall 2.7 Bacterial endospores 2.8 Comparison of the
2、 prokaryotic and eukaryotic cellChapter outline2021/3/112A procaryotic cellA eucaryotic cell Overview of cell structure2021/3/1133. Their cell wall almost always contain the complex polysaccharide peptidoglycanThe prokaryotic cell1. Their genetic material (DNA) is not enclosed within a membrane and
3、they lack other membrane bounded organelles2. Their DNA is not associated with histidine4. They are very small!2021/3/114Size: Most bacteria fall within a range from 0.2 to 2.0 um in diameter and from 2 to 8 um in lengthA rod-shaped prokaryote is typically about 1-5 micrometers (m) long and about 1
4、m wideMicroorganisms in general are very small and are completely invisible to the naked eye. A cyanobacterium 8 x 50 um2021/3/115size comparison of microorganismsVisibility scale Meters Relative size of MicrobesProkaryotesEukaryotesVirusesNaked eyeLight microscopeElectron microscope2021/3/116a cell
5、 increases in size, its surface area to volume ratio decreasesSurface area and volume relationships in cells2021/3/117spirallumShape: Bacteria have a few basic shapesspherical coccusRod-shaped bacillus2021/3/118The cell wall of the bacterial cell is a complex, semi-rigid structure that is responsibl
6、e for the characteristic shape of the cell. The cell wall surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and internal parts of the cell from adverse changes in the surrounding environment.Almost all prokaryotes have cell walls.Prokaryotic cell wall2021/3/119Gram+Gram
7、-Schematic diagram of bacterial cell wallsBacteria can be divided into two major groups, called gram-positive and gram-negative. The original distinction between gram-positive and gram-negative was based on a special staining procedure, the Gram stain 2021/3/1110The Gram-positive cell wall has a pep
8、tidoglycan layer that is relatively thick (ca. 40 nm) and comprises approximately 90% of the cell wall. The cell walls of most Gram-positive eubacteria also have teichoic acids.Gram-positive cell wall2021/3/1111Structure of the Repeating Unit in PeptidoglycanThese constituents are connected to form
9、a repeating structure, the glycan tetrapeptide.Peptidoglycan is composed of two sugar derivatives, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), and a small group of amino acids consisting of L-alanine, D-alanine, D-glutamic acid, and either lysine or diaminopimelic acid (DAP). 2021/3/11
10、122021/3/1113Peptide and glycan units are connected in formation of the peptidoglycan sheet2021/3/1114Gram-positive Bacteria frequently have acidic polysaccharides called teichoic acids attached to their cell wall. The term teichoic acids includes all wall, membrane, or capsular polymers containing
11、glycerophosphate or ribitol phosphate residues. These polyalcohols are connected by phosphate esters and usually have other sugars and D-alanine attached. Teichoic acids2021/3/1115Teichoic acids and lipoteichoic acids are arranged in the overall wall structure of gram-positive Bacteria .Teichoic aci
12、dLipoteichoic acid2021/3/1116The Gram-negative cell wall is a thin layer attached to an outer membrane via lipoproteins. The outer membrane contains phospholipid on its inner surface and lipopolysaccharide (LPS) on its outer surface. The space between the outer membrane and the cytoplasmic membrane
13、is called the periplasmic space.Teichoic acids do not occur in Gram-negative bacterial cell walls. 2021/3/11172021/3/1118O side chainCore polysaccharideLipid AChemical structure of Lipopolysaccharide2021/3/1119Molecular model of E.coli lipopolysaccharide2021/3/1120 The bonds between the carbohydrate
14、s in pseudopeptidoglycan are 1-3 instead of1-4 as in peptidoglycan. CELL WALLS OF ARCHAEBACTERIA The archaebacteria do not contain peptidoglycan in their cell walls as occurs in eubacteria. N-acetylmuramic acid and D-amino acids are not found in the cell walls of archaebacteria.( Differences from eu
15、bacteria )2021/3/1121 Some archaebacteria have walls composed of pseudopeptidoglycan, which resembles the peptidoglycan of eubacteria but contains N-acetyltalosaminuronic acid instead of N-acetylmuramic acid and L.-amino acids instead of the D-amino acids in eubacterial cell walls.2021/3/1122Protopl
16、ast Formation Peptidoglycancan be destroyed by certain agents for instancelysozyme, that breaks the 1,4-glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid in the molecule. 2021/3/1123The difference between gram-positive and gram-negative bacteria is due to the physical nature of t
17、heir cell walls. If the cell wall is removed from gram-positive bacteria, they become gram negative. 2021/3/1124The peptidoglycan seems to act as a permeability barrier preventing loss of crystal violet. Gram-negative peptidoglycan is very thin, not as highly cross-linked, and has larger pores. Alco
18、hol treatment also may extract enough lipid from the gram negative wall to further increase its porosity. For these reasons, alcohol more readily removes the purple crystal violet-iodine complex from gram-negative bacteria.The Mechanism of Gram Staining2021/3/1125 Procedures of Gram Staining2021/3/1
19、126Gram positive or Gram negative?2021/3/1127Morphology of a gram-positive bacterial cell2021/3/1128 Structure of cytoplasmic membrane Function of cytoplasmic membrane2.3 Cytoplasmic membrane2021/3/1129A. The typical cytoplasmic membrane of prokaryotic and eukaryotic cells is a lipid bilayer, as ill
20、ustrated here showing the orientations of the hydrophilic (tan spheres) and hydrophobic (black) ends of phospholipids that make up this structure. B. Colorized electron micrograph ofthe cytoplasmic membrane (CM) of the bacterium Bacillus subtilis reveals the characteristic railroad track appearance
21、of this lipid bilayer.Structure of cytoplasmic membraneIt is a typical UNIT MEMBRANE !2021/3/1130The cytoplasmic membrane, a highly selective barrier, is constructed principally of lipid, within which certain proteins are embedded.Membranes contain both lipids and proteins, although the exact propor
22、tions of lipid and protein vary widely.2021/3/11311. Permeability barrier -prevents leakage and function as gate way for transport of nutrients into and out of the cell.2. Protein anchor- site of many proteins involved in transport, bioenergetics, and chemotaxis.3. Energy conservation- site of gener
23、ation and use of the proton motive force. Function of membrane2021/3/11322021/3/1133Intracellular membrane systemBacteria cells dont contain membrane-enclosed organelles. However, bacteria may have specialized invaginations of the cytoplasmic membrane. Their function may be to provide a larger membr
24、ane surface for greater metabolic activity.2021/3/1134Structure of MesosomeMesosome may be involved in wall formation during division or play a role in chromosome replication and distribution to daughter cells. It may also be involved in secretory processes2021/3/11352.4 Cellular genetic information
25、Bacterial Chromosome1.Supercoiling and chromosome structure2.Chromosomal copy numberPlasmids2021/3/1136Micrograph of a bacterium showing the nucleoid region (green) within the cytoplasm where the bacterial chromosome occurs2021/3/1137The bacterial chromosome is a circular DNA macromolecule except in
26、 Streptomyces where it is linear and Rhodobacter sphaffoides, which has two separate chromosomes. Bacterial chromosomeThe bacterial chromosome is usually a single covalently closed circular molecule.The term nucleoid is used to describe aggregated DNA in the prokaryotic cell.2021/3/1138Range of geno
27、me sizes in virous groups of organisms and the organellesof eukarya2021/3/1139The bacterial chromosome and supercoiling:2021/3/1140Example of E. coli cellThere are over 50 supercoiled domain in the E.coli chromosome.The total amount of DNA is about 4600 kb.If the total DNA is opened and linearized,
28、it would be 1 mm in length.The the cell is only about 2-3 um long. So to package this much DNA into the cell requires that the DNA be highly supercoiled.2021/3/1141Electron micrograph of an isolated nucleoid released from E.coli. 2021/3/1142Chromosome copy number Bacteria that reproduce asexually ar
29、e typically haploid in genetic complement.Rapidly growing cells contain more than 1 copy of the chromosome, and only when cell growth has ceased does the chromosome number approach one per cell.2021/3/1143 Reproduction of a bacterial cell requires the replication of the bacterial chromosome. The mic
30、rograph shows the sequence of synthesis of new circular loops of double helical DNA.Bacteria normally reproduce by binary fission. The inward growth of the septum divides the parent cell to produce two equal-sized progeny cells.2021/3/1144Plasmids dont contain the genetic information for the essenti
31、al metabolic activities of the cell, but they generally do contain genetic information for special features. PlasmidProkaryotic cells have small extra-chromosomal genetic elements called plasmids.2021/3/1145Resistant plasmidsCol plasmidsConjugative plasmidsMetabolic plasmids Major types of plasmids2
32、021/3/1146 2.5 Cytoplasmic matrix Ribosome and Inclusions2021/3/1147All eucaryotic and procaryotic cells contain ribosomes, which function as the sites of protein synthesis. Ribosomes are composed of two subunits Procaryotic ribosomes are called 70S ribosomes, and those of eucaryotic cells are known
33、 as 80S ribosomes RibosomesThe letter S refers to Svedberg units, which indicate the relative rate of sedimentation during ultra-high-speed centrifugation2021/3/11482021/3/1149 Within the cytoplasm of procaryotic (and eucaryotic) cells are several kinds of reserve deposits, known as inclusions. Some
34、 inclusions are common to a wide variety of bacteria, whereas others are limited to a small number of species and therefore serve as a basis for identification. Among the more prominent bacterial inclusions are the following:Carbon storage polymers PHB and glycogenPhosphate polymersSulfur Granules G
35、as VacuolesINCLUSIONS2021/3/1150Polyhydroxybutyric acid (PHB)PHB is a lipidlike compound - one of the most common inclusion bodies in prokaryotic organisms. PHB is commonly found as a storage material and unique to bacteria Glycogen is a starchlike polymer of glucose subunits. Glycogen granules are
36、usually smaller than PHB granules.A Vibrio species2021/3/1151Many microorganisms accumulate granules of polyphosphate, which are large reserves of inorganic phosphates that can be used in the synthesis of ATPPolyphosphate granule in a bacterial cellA Pseudomonas species2021/3/1152The sulfur globules
37、 inside the cells of purple sulfur bacteriumChromatium buderiSome bacteria, including many photosynthetic bacteria, accumulate elemental sulfur granules as a result of their metabolism.2021/3/1153Gas vacuoles (blue) and storage granules (red) in the cyanobacterium MicrocystisThe formation of gas vac
38、uoles by aquatic bacteria provides a mechanism for adjusting the buoyancy of the cell.Many aquatic cyanobacteria use their gas vacuoles to move up and down in the water column.2021/3/11542.6 Components external to the cell wall Flagella Fimbriae and pili Capsules and slime layers2021/3/1155Motility
39、allows the cell to reach different regions of its environment. In the struggle for survival, movement to a new location may mean the difference between survival and death of the cell. But, as in any physical process, cell movement is closely tied to an energy expenditure, and the movement of flagell
40、a is no exception. Many prokaryotes are motile, and this ability to move independently is usually due to a special structure, the flagellum (plural, flagella). 2021/3/1156Four basic types of flagellar arrangementsa, monotrichousb, amphitrichousc, lophotrichousd, peritrichous2021/3/1157Flagella are a
41、rranged differently on different bacteria. In polar flagellation the flagella are attached at one or both ends of the cell. Occasionally a tuft (group) of flagella may arise at one end of the cell, an arrangement called lophotrichous. In peritrichous flagellation the flagella are inserted at many pl
42、aces around the cell surface (peri means around). The type of flagellation, polar or peritrichous, is often used as a characteristic in the classification of bacteria.2021/3/1158The flagellum of a Gram-negative bacterium2021/3/1159The filament of bacterial flagella is composed of subunits of a prote
43、in called flagellin. The base of the flagellum is different in structure from that of the filament. There is a wider region at the base of the flagellum called the hook. The hook consists of a single type of protein and functions to connect the filament to the motor portion of the flagellum. The bas
44、al body is anchored in the cytoplasmic membrane and cell wall. The basal body consists of a small central rod that passes through a system of rings.2021/3/1160In gram-negative Bacteria, an outer ring is anchored in the lipopolysaccharide layer and another in the peptidoglycan layer of the cell wall,
45、 and an inner ring is located within the cytoplasmic membrane.In gram-positive Bacteria, which lack the outer lipopolysaccharide layer, only the inner pair of rings is present. Surrounding the inner ring and anchored in the cytoplasmic membrane are a pair of proteins called Mot . These proteins actu
46、ally drive the flagellar motor causing a torque that rotates the filament. A final set of proteins, called the Fli proteins function as the motor switch, reversing rotation of the flagella in response to intracellular signals.2021/3/1161The movement of a procaryotic flagellum results from rotation o
47、f its basal body and is similar to the movement of the shaft of an electric motor. Bacterial cells can alter the speed and direction of rotation of flagella and thus are capable of various patterns of motility.2021/3/1162Fimbriae can be evenly distributed over the entire surface of the cell. They ca
48、n number anywhere from a few to several hundred per cell. Fimbriae allow a cell to adhere to surfaces including the surfaces of other cells. Pili are usually longer than fimbriae and number only one or two per cell. Pili function to join bacterial cells prior to the transfer of DNA from one cell to
49、another. F pilus2021/3/1163Many prokaryotic organisms secrete on their surfaces slimy or gummy materials. A variety of these structures consist of polysaccharide, and a few consist of protein. The terms capsule and slime layer are frequently used to describe polysaccharide layers.Demonstration of th
50、e presence of a capsule is usually by means of negative staining Capsules and Slime Layers2021/3/1164Many prokaryotes contain a cell surface layer composed of a two-dimensional array of protein. These layers are called S-layers. S-layers have been detected in representatives of virtually every phylo
51、genetic grouping of Bacteria and are nearly universal among Archaea. In some species of Archaea the S-layer is also the cell wall. The major function of S-layers is unknown. However, as the interface between the cell and its environment it is likely that in cells that produce them the S-layer at lea
52、st functions as an external permeability barrier, allowing the passage of low-molecular-weight substances while excluding large molecules. Paracrystalline Surface Layers (S-Layers)2021/3/11652.7 Bacterial endosporesCertain species of bacteria produce special structure called endospores.They are very
53、 resistant to heat and can not be destroyed easily, even by harsh chemicals. Endospores are also resistant to other harmful agents such as drying, radiation, acids and chemical disinfectants.2021/3/1166Sporulating cellCentral coreCortexSpore coat / membraneexosporiumMicrograph of a endosporeVegetati
54、ve cell2021/3/1167 Containing abundant DPA (dipicolinic acid) which is combined with calcium ions. Lower water content only 10-30% of the water content of the vegetative cell. Low pH value, and contains small acid-soluble spore proteins (SASPs)Structure of DPA Properties of endospore and its resista
55、nce 2021/3/1168Sporulation involves a very complex series of events in cellular differentiation. Bacterial sporulation does not occur when cells are dividing exponentially but only when growth ceases owing to the exhaustion of an essential nutrient. Thus, cells of Bacillus cease vegetative growth an
56、d begin sporulation when a key nutrient such as the carbon or nitrogen source becomes limiting.Endospore formatiom2021/3/11691, Axial filament formation2, Septum formatiom3, Engulfment of forespore4, Cortex formation5, Coat synthesis6, Completion of coat synthesis, Increase in refractility and heat
57、resistance7, Lysis of sporangium, spore liberation Stages in endospore formation2021/3/1170Spore germination1. Activation Usually results from treatments like heating.2. Germination Breaks spores dormant state. This process is characterized by spore swelling, loss of resistance to heat and other str
58、esses, loss of refractility and increase in metabolic activity.3. Outgrowth The spore protoplast makes new components and develops once more into an active bacterium.2021/3/1171 Parasporal Crystal(Spore-companioned crystal) Several Bacillus species, most notably B.popilliae and B. thuringiensis, pro
59、duce intracellular crystals of toxic glycoproteins when they sporulate.Toxic crystals2021/3/1172Please carefully read and be familiar with the contents of table 3.3 on the page 100.Comparison of the prokaryotic and eucaryotic cell2021/3/1173Their DNA is associated with histone proteins.membrane-boun
60、ded organelles9+2 type flagellaEucaryotic cell2021/3/1174The chief distinguishing characteristics of procaryotic cells are:1. Their genetic material (DNA) is not enclosed within a membrane.2. They lack other membrane-bounded organelles.3. Their DNA is not associated with histone proteins.4. Their ce
61、ll walls almost always contain the complex polysaccharide peptidoglycan.5. They usually divide by binary fission. During this process, the DNA is copied and the cell splits into two cells. 2021/3/1175Summary1, Prokaryotic genetic material is located in an area called the nucleoid and is not enclosed
62、 by a membrane.2, Most bacteria have a cell wall outside the plasma membrane to give them shape and protect them from osmotic lysis.Bacterial walls are chemically complex and usually contain peptidoglycan or murein.2021/3/11763, Bacteria often are classfied as either gram positive or gram negative b
63、ased on differences in cell wall structure and their response to Gram staining. Gram-positive walls have thick,homogeneous layers of peptidoglycan and teichoid acid. Gram-negative bacteria have a thin peptidoglycan layer surrounded by a complex outer membrane containing lipopolysaccharides and other
64、 components2021/3/11774, Some bacteria are motile, usually by means of flagella, and bacterial species differ in the number and distribution of their flagella.5, Structures such as capsules, fimbriae, and sex pili are found outside of some bacterial cell wall.6, Some bacteria survive adverse environmental conditions by forming endospores, dormant structures resistant to heat,desiccation and many chemicals2021/3/1178
