(优选)微生物学第二章课件

1、（优选）华中农业大学微生物学第二章第1页，共91页。 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 proka

2、ryotic and eukaryotic cellChapter Outline第2页，共91页。ConceptsProkaryotes are small and simple in structure when compared with eukaryotes , yet they often have characteristic shape and size. Prokaryotic genetic material is located in an area called the nucleoid and is not enclosed by a membrane.The prok

3、aryotic cell wall almost always has peptidoglycan and is chemically and morphologically complex. 第3页，共91页。A procaryotic cellA eucaryotic cell 2.1 Overview of Cell Structure第4页，共91页。3. Their cell wall almost always contain the complex polysaccharide peptidoglycanThe Prokaryotic Cell1. Their genetic m

4、aterial (DNA) is not enclosed within a membrane and they lack other membrane bounded organelles2. Their DNA is not associated with histidine4. They are very small!第5页，共91页。Schematic diagram of a bacterial cell第6页，共91页。Size: Most bacteria fall within a range from 0.2 to 2.0 um in diameter and from 2

5、to 8 um in lengthA rod-shaped prokaryote is typically about 1-5 micrometers (m) long and about 1 m wideMicroorganisms in general are very small and are completely invisible to the naked eye. A cyanobacterium 8 x 50 um第7页，共91页。size comparison of microorganismsVisibility scale Meters Relative size of

6、MicrobesProkaryotesEukaryotesVirusesNaked eyeLight microscopeElectron microscope第8页，共91页。a cell increases in size, its surface area to volume ratio decreasesSurface area and volume relationships in cells第9页，共91页。spirallumShape: Bacteria have a few basic shapesspherical coccusRod-shaped bacillus第10页，

7、共91页。 2.2 Prokaryotic Cell WallCell Wall第11页，共91页。The cell wall of the bacterial cell is a complex, semi-rigid structure that is responsible for the characteristic shape of the cell. The cell wall surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and internal parts of t

8、he cell from adverse changes in the surrounding environment.Almost all prokaryotes have cell walls.第12页，共91页。Gram+Gram-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 gr

9、am-negative was based on a special staining procedure, the Gram stain 第13页，共91页。The Gram-positive cell wall has a peptidoglycan 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-p

10、ositive Cell Wall第14页，共91页。Structure of the Repeating Unit in PeptidoglycanThese constituents are connected to form 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

11、acids consisting of L-alanine, D-alanine, D-glutamic acid, and either lysine or diaminopimelic acid (DAP). 第15页，共91页。第16页，共91页。Peptide and glycan units are connected in formation of the peptidoglycan sheet第17页，共91页。Gram-positive Bacteria frequently have acidic polysaccharides called teichoic acids a

12、ttached to their cell wall. The term teichoic acids includes all wall, membrane, or capsular polymers containing glycerophosphate or ribitol phosphate residues. These polyalcohols are connected by phosphate esters and usually have other sugars and D-alanine attached. Teichoic Acids第18页，共91页。Teichoic

13、 acids and lipoteichoic acids are arranged in the overall wall structure of gram-positive Bacteria .Teichoic acidLipoteichoic acid第19页，共91页。The 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 li

14、popolysaccharide (LPS) on its outer surface. The space between the outer membrane and the cytoplasmic membrane is called the periplasmic space.Teichoic acids do not occur in Gram-negative bacterial cell walls. 第20页，共91页。第21页，共91页。O side chainCore polysaccharideLipid AChemical Structure of Lipopolysa

15、ccharide第22页，共91页。Molecular Model of E.coli Lipopolysaccharide第23页，共91页。The bonds between the carbohydrates in pseudopeptidoglycan are 1-3 instead of1- 4 as in peptidoglycan. Cell Walls of ArchaebacteriaThe archaebacteria do not contain peptidoglycan in their cell walls as occurs in eubacteria.N-ace

16、tylmuramic acid and D-amino acids are not found in the cell walls of archaebacteria. ( Differences from eubacteria )第24页，共91页。Some archaebacteria have walls composed of pseudopeptidoglycan, which resembles the peptidoglycan of eubacteria but contains N-acetyltalosaminuronic acid instead of N-acetylm

17、uramic acid and L.-amino acids instead of the D-amino acids in eubacterial cell walls.第25页，共91页。Protoplast 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. 第26页，共

18、91页。The difference between gram-positive and gram-negative bacteria is due to the physical nature of their cell walls. If the cell wall is removed from gram-positive bacteria, they become gram negative. 第27页，共91页。The peptidoglycan seems to act as a permeability barrier preventing loss of crystal vio

19、let. Gram-negative peptidoglycan is very thin, not as highly cross-linked, and has larger pores. Alcohol 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

20、 gram-negative bacteria.The Mechanism of Gram Staining第28页，共91页。 Procedures of Gram Staining第29页，共91页。Gram positive or Gram negative?第30页，共91页。第31页，共91页。 Structure of cytoplasmic membrane 2.3 Cytoplasmic Membrane Function of cytoplasmic membraneMembrane第32页，共91页。B. Colorized electron micrograph of t

21、he cytoplasmic membrane (CM) of the bacterium Bacillus subtilis reveals the characteristic railroad track appearance of this lipid bilayer. Structure of Cytoplasmic MembraneIt is a typical UNIT MEMBRANE !A. The typical cytoplasmic membrane of prokaryotic and eukaryotic cells is a lipid bilayer, as i

22、llustrated here showing the orientations of the hydrophilic (tan spheres) and hydrophobic (black) ends of phospholipids that make up this structure. 第33页，共91页。The cytoplasmic membrane, a highly selective barrier, is constructed principally of lipid, within which certain proteins are embedded.Membran

23、es contain both lipids and proteins, although the exact proportions of lipid and protein vary widely.第34页，共91页。 Diagram of the structure of cytoplasmic membrane第35页，共91页。3. Energy conservation- site of generation and use of the proton motive force. Function of Membrane1. Permeability barrier -preven

24、ts 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.第36页，共91页。 Rate of permeability* 100 0.1 0.001 0.001 0.000001 0.0000001 0.00000001 Substance Water Glycerol Tryptophan

25、 Glucose Chloride ion (Cl-) Patassium ion (K+) Sodium ion (Na+) * Relative rate: Permeability with respect to permeability of water given as 100 Comparative permeability of membrane molecules to various 第37页，共91页。Intracellular Membrane SystemBacteria cells dont contain membrane-enclosed organelles.

26、However, bacteria may have specialized invaginations of the cytoplasmic membrane. Their function may be to provide a larger membrane surface for greater metabolic activity.第38页，共91页。Structure of MesosomeMesosome may be involved in wall formation during division or play a role in chromosome replicati

27、on and distribution to daughter cells. It may also be involved in secretory processes第39页，共91页。2.4 Cellular Genetic InformationNucleoid第40页，共91页。Bacterial ChromosomeSupercoiling and chromosome structureChromosomal copy number2. Plasmids第41页，共91页。Micrograph of a bacterium showing the nucleoid region

28、(green) within the cytoplasm where the bacterial chromosome occurs第42页，共91页。The bacterial chromosome is a circular DNA macromolecule except in Streptomyces where it is linear and Rhodobacter sphaffoides, which has two separate chromosomes. Bacterial ChromosomeThe bacterial chromosome is usually a si

29、ngle covalently closed circular molecule.The term nucleoid is used to describe aggregated DNA in the prokaryotic cell.第43页，共91页。Range of genome sizes in virous groups of organisms and the organellesof eukarya第44页，共91页。The bacterial chromosome and supercoiling:第45页，共91页。Example of E. coli cellThere a

30、re 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, 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.第46页，共91

31、页。Electron micrograph of an isolated nucleoid released from E.coli. 第47页，共91页。Chromosome copy number Bacteria that reproduce asexually are 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 chromosom

32、e number approach one per cell.第48页，共91页。 Reproduction of a bacterial cell requires the replication of the bacterial chromosome. The micrograph 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 d

33、ivides the parent cell to produce two equal-sized progeny cells.第49页，共91页。Plasmids dont contain the genetic information for the essential metabolic activities of the cell, but they generally do contain genetic information for special features. PlasmidProkaryotic cells have small extra-chromosomal ge

34、netic elements called plasmids.第50页，共91页。Resistant plasmidsCol plasmidsConjugative plasmidsMetabolic plasmids Major Types of Plasmids第51页，共91页。2.5 Cytoplasmic Matrix Ribosome and InclusionsRibosomeCarbon storage polymers PHB and glycogenPhosphate polymersSulfur Granules Gas Vacuoles第52页，共91页。All euc

35、aryotic 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 as 80S ribosomes RibosomesThe letter S refers to Svedberg units, which ind

36、icate the relative rate of sedimentation during ultra-high-speed centrifugation第53页，共91页。第54页，共91页。 Within the cytoplasm of procaryotic (and eucaryotic) cells are several kinds of reserve deposits, known as inclusions. Some inclusions are common to a wide variety of bacteria, whereas others are limi

37、ted to a small number of species and therefore serve as a basis for identification. Among the more prominent bacterial inclusions are the following:Inclusion Carbon storage polymers PHB and glycogen Phosphate polymers Sulfur Granules Gas Vacuoles第55页，共91页。Polyhydroxybutyric acid (PHB)PHB is a lipidl

38、ike 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 usually smaller than PHB granules.A Vibrio species第56页，共91页。Many microorgani

39、sms 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 species第57页，共91页。The sulfur globules inside the cells of purple sulfur bacteriumChromatium buderiSome bacteria, in

40、cluding many photosynthetic bacteria, accumulate elemental sulfur granules as a result of their metabolism.第58页，共91页。Gas vacuoles (blue) and storage granules (red) in the cyanobacterium MicrocystisThe formation of gas vacuoles by aquatic bacteria provides a mechanism for adjusting the buoyancy of th

41、e cell.Many aquatic cyanobacteria use their gas vacuoles to move up and down in the water column.第59页，共91页。2.6 Components external to the cell wall Flagella Fimbriae and pili Capsules and slime layers第60页，共91页。Motility allows the cell to reach different regions of its environment. In the struggle fo

42、r 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 flagella is no exception. Many prokaryotes are motile, and this ability to move independ

43、ently is usually due to a special structure, the flagellum (plural, flagella). 第61页，共91页。第62页，共91页。Four basic types of flagellar arrangementsa. monotrichousb. amphitrichousc. lophotrichousd. peritrichous第63页，共91页。Flagella are arranged differently on different bacteria. In polar flagellation the flag

44、ella 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 places around the cell surface (peri means around). The type of flagellatio

45、n, polar or peritrichous, is often used as a characteristic in the classification of bacteria.第64页，共91页。 The flagellum of a Gram-negative bacterium第65页，共91页。The filament of bacterial flagella is composed of subunits of a protein called flagellin. The base of the flagellum is different in structure f

46、rom 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 basal body is anchored in the cytoplasmic membrane and cell wall. The basal b

47、ody consists of a small central rod that passes through a system of rings.第66页，共91页。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

48、 . These proteins actually 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.In gram-negative Bacteria, an outer ring is anchored

49、 in the lipopolysaccharide layer and another in the peptidoglycan layer of the cell wall, and an inner ring is located within the cytoplasmic membrane.第67页，共91页。The movement of a procaryotic flagellum results from rotation of its basal body and is similar to the movement of the shaft of an electric

50、motor. Bacterial cells can alter the speed and direction of rotation of flagella and thus are capable of various patterns of motility.第68页，共91页。Fimbriae can be evenly distributed over the entire surface of the cell. They can number anywhere from a few to several hundred per cell. Fimbriae allow a ce

51、ll 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 another. F pilus第69页，共91页。Many prokaryotes contain a cell surface layer compo

52、sed of a two-dimensional array of protein. These layers are called S-layers.S-layers have been detected in representatives of virtually every phylogenetic grouping of Bacteria and are nearly universal among Archaea. In some species of Archaea the S-layer is also the cell wall. Paracrystalline Surfac

53、e Layers (S-Layers)第70页，共91页。The major function of S-layers is unknown. As the interface between the cell and its environment ,it is likely that in cells that produce them the S-layer at least functions as an external permeability barrier, allowing the passage of low-molecular-weight substances whil

54、e excluding large molecules. 第71页，共91页。2.7 Bacterial EndosporesCertain species of bacteria produce special structure called endospores.They are very resistant to heat and can not be destroyed easily, even by harsh chemicals. Endospores are also resistant to other harmful agents such as drying, UV ra

55、diation, acids and chemical disinfectants.第72页，共91页。Sporulating cellCentral coreCortexSpore coat / membraneexosporiumMicrograph of a endosporeVegetative cell第73页，共91页。第74页，共91页。Many prokaryotic organisms secrete on their surfaces slimy or gummy materials. A variety of these structures consist of pol

56、ysaccharide, and a few consist of protein. The terms capsule and slime layer are frequently used to describe polysaccharide layers.Demonstration of the presence of a capsule is usually by means of negative staining Capsules and Slime Layers第75页，共91页。Low pH value, and contains small acid-soluble spor

57、e proteins (SASPs)Structure of DPA Properties of Endospore and Its Resistance 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.第76页，共91页。Sporulation involves a very complex series of events in c

58、ellular 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 and begin sporulation when a key nutrient such as the carbon or nitrogen s

59、ource becomes limiting.Endospore Formatiom第77页，共91页。 Stages in endospore formation1. Axial filament formation2. Septum formatiom3. Engulfment of forespore4. Cortex formation5. Coat synthesis6. Completion of coat synthesis, Increase in refractility and heat resistance7. Lysis of sporangium, spore lib

60、eration第78页，共91页。第79页，共91页。1. 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 stresses, loss of refractility and increase in metabolic activity.3. Outgrowth The s