华中农业大学微生物英文.pptx

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1、 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 prokaryotic and eukaryotic cell

2、Chapter outline第1页/共78页A procaryotic cellA eucaryotic cell Overview of cell structure第2页/共78页3.Their cell wall almost always contain the complex polysaccharide peptidoglycanThe prokaryotic cell1.Their genetic material(DNA)is not enclosed within a membrane and they lack other membrane bounded organel

3、les2.Their DNA is not associated with histidine4.They are very small!第3页/共78页Size: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 m wideMicroorganisms in general are very small

4、and are completely invisible to the naked eye.A cyanobacterium 8 x 50 um第4页/共78页size comparison of microorganismsVisibility scale Meters Relative size of MicrobesProkaryotesEukaryotesVirusesNaked eyeLight microscopeElectron microscope第5页/共78页a cell increases in size,its surface area to volume ratio

5、decreasesSurface area and volume relationships in cells第6页/共78页spirallumShape:Bacteria have a few basic shapesspherical coccusRod-shaped bacillus第7页/共78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 su

6、rrounds 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 wall第8页/共78页Gram+Gram-Schematic diagram of bacterial cell wallsBacteria can be divided

7、 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 第9页/共78页The Gram-positive cell wall has a peptidoglycan layer that is relatively thick(ca.40 nm)and comprises approx

8、imately 90%of the cell wall.The cell walls of most Gram-positive eubacteria also have teichoic acids.Gram-positive cell wall第10页/共78页Structure of the Repeating Unit in PeptidoglycanThese constituents are connected to form a repeating structure,the glycan tetrapeptide.Peptidoglycan is composed of two

9、 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).第11页/共78页第12页/共78页Peptide and glycan units are connected in formation of the peptidoglycan sheet第1

10、3页/共78页Gram-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 glycerophosphate or ribitol phosphate residues.These polyalcohols are connected by phosphate ester

11、s and usually have other sugars and D-alanine attached.Teichoic acids第14页/共78页Teichoic acids and lipoteichoic acids are arranged in the overall wall structure of gram-positive Bacteria.Teichoic acidLipoteichoic acid第15页/共78页The Gram-negative cell wall is a thin layer attached to an outer membrane vi

12、a 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 is called the periplasmic space.Teichoic acids do not occur in Gram-negative bacterial cell walls.第16页/共78页第1

13、7页/共78页O side chainCore polysaccharideLipid AChemical structure of Lipopolysaccharide第18页/共78页Molecular model of E.coli lipopolysaccharide第19页/共78页 The bonds between the carbohydrates in pseudopeptidoglycan are 1-3 instead of1-4 as in peptidoglycan.CELL WALLS OF ARCHAEBACTERIA The archaebacteria do

14、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 eubacteria)第20页/共78页 Some archaebacteria have walls composed of pseudopeptidoglycan,which resembles the peptidoglycan of eu

15、bacteria but contains N-acetyltalosaminuronic acid instead of N-acetylmuramic acid and L.-amino acids instead of the D-amino acids in eubacterial cell walls.第21页/共78页Protoplast Formation Peptidoglycancan be destroyed by certain agents for instancelysozyme,that breaks the 1,4-glycosidic bonds between

16、 N-acetylglucosamine and N-acetylmuramic acid in the molecule.第22页/共78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23页/共78页The peptidoglycan seems

17、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.Alcohol treatment also may extract enough lipid from the gram negative wall to further increase its porosity.For these reasons,alcohol more read

18、ily removes the purple crystal violet-iodine complex from gram-negative bacteria.The Mechanism of Gram Staining第24页/共78页 Procedures of Gram Staining第25页/共78页Gram positive or Gram negative?第26页/共78页Morphology of a gram-positive bacterial cell第27页/共78页 Structure of cytoplasmic membrane Function of cyt

19、oplasmic membrane2.3 Cytoplasmic membrane第28页/共78页A.The typical cytoplasmic membrane of prokaryotic and eukaryotic cells is a lipid bilayer,as illustrated here showing the orientations of the hydrophilic(tan spheres)and hydrophobic(black)ends of phospholipids that make up this structure.B.Colorized

20、electron micrograph ofthe 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!第29页/共78页The cytoplasmic membrane,a highly selective barrier,is constructed p

21、rincipally of lipid,within which certain proteins are embedded.Membranes contain both lipids and proteins,although the exact proportions of lipid and protein vary widely.第30页/共78页1.Permeability barrier-prevents leakage and function as gate way for transport of nutrients into and out of the cell.2.Pr

22、otein anchor-site of many proteins involved in transport,bioenergetics,and chemotaxis.3.Energy conservation-site of generation and use of the proton motive force.Function of membrane第31页/共78页第32页/共78页Intracellular membrane systemBacteria cells dont contain membrane-enclosed organelles.However,bacter

23、ia may have specialized invaginations of the cytoplasmic membrane.Their function may be to provide a larger membrane surface for greater metabolic activity.第33页/共78页Structure of MesosomeMesosome may be involved in wall formation during division or play a role in chromosome replication and distributi

24、on to daughter cells.It may also be involved in secretory processes第34页/共78页2.4 Cellular genetic informationBacterial Chromosome1.Supercoiling and chromosome structure2.Chromosomal copy numberPlasmids第35页/共78页Micrograph of a bacterium showing the nucleoid region(green)within the cytoplasm where the

25、bacterial chromosome occurs第36页/共78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 single covalently closed circular molecule.T

26、he term nucleoid is used to describe aggregated DNA in the prokaryotic cell.第37页/共78页Range of genome sizes in virous groups of organisms and the organellesof eukarya第38页/共78页The bacterial chromosome and supercoiling:第39页/共78页Example of E.coli cellThere are over 50 supercoiled domain in the E.coli ch

27、romosome.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40页/共78页Electron micrograph of an isolated nucleoid rel

28、eased from E.coli.第41页/共78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 chromosome number approach one per cell.第42页/共78页 Reproductio

29、n 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 divides the parent cell to produce two equal-sized proge

30、ny cells.第43页/共78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 genetic elements called plasmids.第44页/共78页Resistant plasmids

31、Col plasmidsConjugative plasmidsMetabolic plasmids Major types of plasmids第45页/共78页 2.5 Cytoplasmic matrix Ribosome and Inclusions第46页/共78页All eucaryotic and procaryotic cells contain ribosomes,which function as the sites of protein synthesis.Ribosomes are composed of two subunits Procaryotic riboso

32、mes are called 70S ribosomes,and those of eucaryotic cells are known as 80S ribosomes RibosomesThe letter S refers to Svedberg units,which indicate the relative rate of sedimentation during ultra-high-speed centrifugation第47页/共78页第48页/共78页 Within the cytoplasm of procaryotic(and eucaryotic)cells are

33、 several kinds of reserve deposits,known as inclusions.Some 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 pol

34、ymers PHB and glycogenPhosphate polymersSulfur Granules Gas VacuolesINCLUSIONS第49页/共78页Polyhydroxybutyric 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

35、polymer of glucose subunits.Glycogen granules are usually smaller than PHB granules.A Vibrio species第50页/共78页Many 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 Ps

36、eudomonas species第51页/共78页The sulfur globules inside the cells of purple sulfur bacteriumChromatium buderiSome bacteria,including many photosynthetic bacteria,accumulate elemental sulfur granules as a result of their metabolism.第52页/共78页Gas vacuoles(blue)and storage granules(red)in the cyanobacteriu

37、m MicrocystisThe formation of gas vacuoles 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.第53页/共78页2.6 Components external to the cell wall Flagella Fimbriae and pili Capsules a

38、nd slime layers第54页/共78页Motility 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,

39、and the movement of flagella is no exception.Many prokaryotes are motile,and this ability to move independently is usually due to a special structure,the flagellum(plural,flagella).第55页/共78页Four basic types of flagellar arrangementsa,monotrichousb,amphitrichousc,lophotrichousd,peritrichous第56页/共78页F

40、lagella are arranged 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

41、many places 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.第57页/共78页The flagellum of a Gram-negative bacterium第58页/共78页The filament of bacterial flagella is composed of subunits of a protei

42、n 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 basal bo

43、dy 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.第59页/共78页In gram-negative Bacteria,an outer ring is anchored in the lipopolysaccharide layer and another in the peptidoglycan layer of the cell wall,and an in

44、ner 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 actually drive the

45、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.第60页/共78页The movement of a procaryotic flagellum results from rotation of its basal body and

46、 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.第61页/共78页Fimbriae can be evenly distributed over the entire surface of the cell.They can number anywhere from a

47、 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 another.F pilus第62页/共78页Man

48、y 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 the presence of a capsule is usuall

49、y by means of negative staining Capsules and Slime Layers第63页/共78页Many 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 phylogenetic grouping of Bacteria and are

50、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 least functions as an external permeability