membrane called the cytoplasmic (orplasma)membrane,surroundedby a thick layer ofpeptidoglycan (20-80 nm). The Gram-negative bacteria have only a thin layer of peptidoglycan(1-3nm)but on the outside ofthis there is a further outermembrane which acts as an additionalbarrier.TheprocedurefortheGram stain isas follows.Fixed cells arestained withadark stain suchas crystal violet, followed by iodine which complexes with the stain in the cell wall of thebacteria. Alcohol is added, which washes the dark stain of crystal violet-iodine out of ceils thathave thin cell walls but notfromthose that havethick cell walls.Finally,a paler stain such ascarbol fuschin, called a counter stain, is added which stains the decolorized cells pink but is notseen on the dark staining cells that retained the first stain. The cells that retain the stain (with thickcell walls) are called Gram-positive and appear dark purple under light microscopy. The onesthat lose the stain (with thin cell walls and anouter membrane)arecalled Gram-negativeandstainpinkorpalepurpleThe Cell Wall1Thecell wall surrounds theplasma membraneandprotects the cell fromchanges inosmoticpressure（渗透压）and provides rigidity and strength.2The bacterial cell wall consists of peptidoglycan（肽聚糖），a polymer consisting of NAGand NAM and short chains of amino acids.3.Gram-positive（革兰氏阳性）cell walls consistofmanylayersof peptidoglycan and alsocontainteichoicacids（垣酸），x.Gram-negative（革兰氏阴性）bacteriahavealipidprotein-lipopolysaccharide-phospholipidouter membrane surrounding a thin peptidoglycan layer.5.Theoutermembrane protects the cellfrom phagocytosis and penicillin（青霉素），lysozyme（溶菌酶），and other chemicals.6.Porins（孔蛋白）areproteins thatpermit smallmolecules topass throughtheoutermembrane; specific channel proteins allow other molecules to move through the outermembrane.7.Thelipopolysaccharide（脂多糖，LPs）component ofthe outermembrane consists ofsugars that function as antigens and lipidA,which is an endotoxin（内毒素）teichoic acid:Gram-positive cell walls also contain large amounts of another polymer, called teichoic acid,made up of glycerol or ribitol joined by phosphate groups.D-Ala, glucose or sugars may beattached to the glycerol or ribitol and the polymers are attached either directly to the NAM in thepeptidoglycan or to lipids in the membrane (in this case they are called lipoteichoic acids). Thefunction of these molecules is unclear but they may have arole in maintaining the structure of the6
6 membrane called the cytoplasmic (or plasma) membrane, surrounded by a thick layer of peptidoglycan (20-80 nm). The Gram-negative bacteria have only a thin layer of peptidoglycan (1-3 nm) but on the outside of this there is a further outer membrane which acts as an additional barrier. The procedure for the Gram stain is as follows. Fixed cells are stained with a dark stain such as crystal violet, followed by iodine which complexes with the stain in the cell wall of the bacteria. Alcohol is added, which washes the dark stain of crystal violet-iodine out of ceils that have thin cell walls but not from those that have thick cell walls. Finally, a paler stain such as carbol fuschin, called a counter stain, is added which stains the decolorized cells pink but is not seen on the dark staining cells that retained the first stain. The cells that retain the stain (with thick cell walls) are called Gram-positive and appear dark purple under light microscopy. The ones that lose the stain (with thin cell walls and an outer membrane) are called Gram-negative and stain pink or pale purple The Cell Wall 1. The cell wall surrounds the plasma membrane and protects the cell from changes in osmotic pressure（渗透压）and provides rigidity and strength. 2. The bacterial cell wall consists of peptidoglycan（肽聚糖）, a polymer consisting of NAG and NAM and short chains of amino acids. 3. Gram-positive（革兰氏阳性） cell walls consist of many layers of peptidoglycan and also contain teichoic acids（垣酸）. 4. Gram-negative（革兰氏阴性）bacteria have a lipidprotein-lipopolysaccharide-phospholip id outer membrane surrounding a thin peptidoglycan layer. 5. The outer membrane protects the cell from phagocytosis and penicillin（青霉素）, lysozyme （溶菌酶）, and other chemicals. 6. Porins（孔蛋白）are proteins that permit small molecules to pass through the outer membrane; specific channel proteins allow other molecules to move through the outer membrane. 7. The lipopolysaccharide（脂多糖，LPS） component of the outer membrane consists of sugars that function as antigens and lipid A, which is an endotoxin（内毒素）. teichoic acid: Gram-positive cell walls also contain large amounts of another polymer, called teichoic acid, made up of glycerol or ribitol joined by phosphate groups. D-Ala, glucose or sugars may be attached to the glycerol or ribitol and the polymers are attached either directly to the NAM in the peptidoglycan or to lipids in the membrane (in this case they are called lipoteichoic acids). The function of these molecules is unclear but they may have a role in maintaining the structure of the
cell wall and in the control ofautolysis.periplasmicspace（周质空间）The outer membrane of Gram-negative bacteria acts as an additional barrier protecting thepeptidoglycan from toxic compounds such as lysozyme which act on the cell wall. It createsan aqueous space between the twomembranes called theperiplasmic space which is thoughtto have a gel-like structure with a loose network of peptidoglycan running through it.Estimates as to the width of thepeptidoglycan varyfrom1-71 nm but it has proved to bedifficultto obtain a real definitive value.The periplasmic space contains a range of proteinsassociated with:.transport ofnutrientsintothecell:.enzymes that are involved in nutrientacquisition such as proteases;:enzymes that defend the cell againsttoxic chemicals such as B-lactamases that destroypenicillin.outermembraneThe outer membrane of Gram-negative bacteria is made up of phospholipidsmembrane,but it also contains some unique featuresPoresformedbyproteins called porins such asOmpFandOmpCthatallowthepassivediffusionof smallmoleculesintotheperiplasmicspace2.An abundant small lipoprotein called Braun's lipoprotein thatiscovalentlybound tothepeptidoglycan andis embedded intheoutermembranebyit shydrophobic lipid,therefore holding the peptidoglycan and outer membraneclose together.LPS molecules are found in the outer leaflet of the outer membrane projecting into the3.surroundingmedium.Atypical（缺陷的）cellwalls1.Mycoplasma（支原体）is a bacterial genus that naturallylackscellwalls2.Archaeobacteriahavepseudomurein（假肽聚糖）；theylackpeptidoglycan3..Lforms aremutantbacteria withdefective cell walls.Archaeobacterial cell wallsOne of the distinctive features of archaebacteria is the nature of the lipids in the plasmamembrane which, unlike the ester-linked lipids of eubacteria and eukaryotes are ether-linked toglycerol. They are also long chained and branched. Archaebacterial cell walls and envelopesshowgreat diversityand complexity in structure.They do notcontain peptidoglycan although somedo have a similar compound called pseudomurein which contains N-acetyl-alosaminuronic acid inplace of muramic acid.Another common type of cell wall is the S-layer,a two-dimensional,paracrystalline, array of protein or glycoprotein on the cell surface. Others have thick7
7 cell wall and in the control of autolysis. periplasmic space（周质空间） The outer membrane of Gram-negative bacteria acts as an additional barrier protecting the peptidoglycan from toxic compounds such as lysozyme which act on the cell wall. It creates an aqueous space between the two membranes called the periplasmic space which is thought to have a gel-like structure with a loose network of peptidoglycan running through it. Estimates as to the width of the peptidoglycan vary from 1-71 nm but it has proved to be difficult to obtain a real definitive value. The periplasmic space contains a range of proteins associated with: • transport of nutrients into the cell; • enzymes that are involved in nutrient acquisition such as proteases; • enzymes that defend the cell against toxic chemicals such as в-lactamases that destroy penicillin. outer membrane The outer membrane of Gram-negative bacteria is made up of phospholipids membrane,but it also contains some unique features 1. Pores formed by proteins called porins such as OmpF and OmpC that allow the passive diffusion of small molecules into the periplasmi c space. 2. An abundant small lipoprotein called Braun's lipoprotein that is covalentlybound to the peptidoglycan and is embedded in the outer membrane by it s hydrophobic lipid, therefore holding the peptidoglycan and outer membraneclose together. 3. LPS molecules are found in the outer leaflet of the outer membrane projecting into the surrounding medium. Atypical（缺陷的） cell walls 1. Mycoplasma（支原体） is a bacterial genus that naturally lacks cell walls. 2. Archaeobacteria have pseudomurein（假肽聚糖）; they lack peptidoglycan. 3. .L forms are mutant bacteria with defective cell walls. Archaeobacterial cell walls One of the distinctive features of archaebacteria is the nature of the lipids in the plasma membrane which, unlike the ester-linked lipids of eubacteria and eukaryotes are ether-linked to glycerol. They are also long chained and branched. Archaebacterial cell walls and envelopes show great diversity and complexity in structure. They do not contain peptidoglycan although some do have a similar compound called pseudomurein which contains N-acetyl-alosaminuronic acid in place of muramic acid. Another common type of cell wall is the S-layer, a two-dimensional, paracrystalline, array of protein or glycoprotein on the cell surface. Others have thick
polysaccharidewallsoutsidetheirplasmamembraneDAMAGETOTHECELLWALLpeptidoglycan used to be a target for antimicrobial agents that destroy prokaryotic cellsspecifically, but do not harm eukaryotic cells, an example ofthis is the antibiotic penicillin(TopicF7).Lysozyme, a natural antibacterial agent found in tears and natural secretions, breaks down thelinkagebetweenNAM and NAG.Removal of the cell wall under conditions wherethe osmolarityof the medium is the same as the inside of the cell (isotonic solution) results in the formation ofroundprotoplasts（原生质体）（Gram-positives）orspheroplasts（球形体）（Gram-negatives）which survive as long as the isotonicity is maintained. These structures lyse, however, if placed ina dilute medium, illustrating the importance of peptidoglycan to the cells survival.1.In the presence of lysozyme, gram-positive cell walls are destroyed and the remainingcellular contents are referred to as a protoplast.2.In the presence of lysozyme, gram-negative cell walls are not completely destroyed andthe remaining cellular contents are referred to as a spheroplast.3.Protoplasts and spheroplasts are subject to osmotic lysis4.Antibiotics suchaspenicillin interferewithcell wall synthesisPLASMA (CYTOPLASMIC) MEMBRANEThe plasma membrane encloses the cytoplasm and is a phospholipid bilayer withprotein (fluid mosaic).2mostofbacterialackofsteriol（固醇）3The plasma membrane is selectively permeable.4Plasma membranes carry enzymes for metabolic reactions, such as nutrientbreakdown, energy production, and photosynthesis.5Mesosomes-irregularinfoldings oftheplasmamembrane-are nowconsideredartifacts6.PlasmamembranescanbedestroyedbyalcoholsandpolymyxinCYTOPLASM1Cytoplasmis thefluidcomponent insidetheplasmamembrane.2The cytoplasm is mostly water,with inorganicand organic molecules,DNA,ribosomes, and inclusions.RIBOSOMESThe cytoplasm of a procaryote contains numerous 70S ribosomes,ribosomes consist ofrRNA and protein.2Proteinsynthesis occursatribosomes,thiscanbeinhibited bycertainantibioticsINCLUSIONS8
8 polysaccharide walls outside their plasma membrane. DAMAGE TO THE CELL WALL peptidoglycan used to be a target for antimicrobial agents that destroy prokaryotic cells specifically, but do not harm eukaryotic cells; an example of this is the antibiotic penicillin (Topic F7). Lysozyme, a natural antibacterial agent found in tears and natural secretions, breaks down the linkage between NAM and NAG. Removal of the cell wall under conditions where the osmolarity of the medium is the same as the inside of the cell (isotonic solution) results in the formation of round protoplasts(原生质体) (Gram-positives) or spheroplasts(球形体) (Gram-negatives) which survive as long as the isotonicity is maintained. These structures lyse, however, if placed in a dilute medium, illustrating the importance of peptidoglycan to the cells' survival. 1. In the presence of lysozyme, gram-positive cell walls are destroyed and the remaining cellular contents are referred to as a protoplast. 2. In the presence of lysozyme, gram-negative cell walls are not completely destroyed and the remaining cellular contents are referred to as a spheroplast. 3. Protoplasts and spheroplasts are subject to osmotic lysis. 4. Antibiotics such as penicillin interfere with cell wall synthesis. PLASMA (CYTOPLASMIC) MEMBRANE 1 The plasma membrane encloses the cytoplasm and is a phospholipid bilayer with protein (fluid mosaic). 2 most of bacteria lack of steriol（固醇） 3 The plasma membrane is selectively permeable. 4 Plasma membranes carry enzymes for metabolic reactions, such as nutrient breakdown, energy production, and photosynthesis. 5 Mesosomes—irregular infoldings of the plasma membrane—are now considered artifacts 6 .Plasma membranes can be destroyed by alcohols and polymyxin. CYTOPLASM 1 Cytoplasm is the fluid component inside the plasma membrane. 2 The cytoplasm is mostly water, with inorganic and organic molecules, DNA, ribosomes, and inclusions. RIBOSOMES 1 The cytoplasm of a procaryote contains numerous 70S ribosomes; ribosomes consist of rRNA and protein. 2 Protein synthesis occurs at ribosomes; this can be inhibited by certain antibiotics. INCLUSIONS
Inclusions（内含物）arereservedepositsfoundinprocaryoticandeucaryoticcellsE2Amongtheinclusionsfoundinbacteriaaremetachromaticgranules（异染粒）（inorganicphosphate),polysaccharide granules(，多糖，usually glycogen orstarch),lipid inclusions（脂滴），sulfurgranules（硫粒），carboxysomes（，羧酶体，ribulose1,5-diphosphatecarboxylase)，andgasvacuoles（气泡）NUCLEARAREA1.The nuclear area contains the DNA of the bacterial chromosome.Bacteria can also containplasmids, which are extrachromosomal DNA circles.capsule or slime layercapsule（英膜）orslime（黏液层）layerisagelatinous polysaccharideand/orpolypeptidecovering.2.Capsulesmayprotectpathogensfromphagocytosis（吞噬）3.Capsules provideadherence to surfaces,prevent desiccation,andmayprovidenutrientsFLAGELLA1.Flagella（鞭毛）arerelativelylongfilamentousappendagesconsistingofafilamenthookand basal body.2Procaryoticflagellarotatetopushthecell.Motile（运动）3.bacteria exhibit taxis （趋性）positive taxis is movement toward an attractant andnegativetaxisismovementawayfromarepellent.FIMBRIAEANDPILIF1fimbriae（菌毛）and pili（性毛）are shortthin appendages2Fimbriae help cells adhere to surfaces3.Pili join cells for the transfer of DNA from one cell to anotherENDOSPORES（芽孢）Endospores are resting structures formed by some bacteria for survival during adverseenvironmental conditions.2.Theprocess of endosporeformation is called sporulation; the return ofan endosporeto itsvegetative state iscalled germinationEndospores are a method as survival, not one of reproduction. Certain bacteria will form a sporewithintheircellmembrane(an endospore)that allowsthemtowaitoutdeterioratingenvironmentalconditions.Certaindisease causingbacteria (such as the one that causes the disease Anthrax)canbevirulent(capableof causingan infection)1300yearsafterformingtheirendospore!)BACTERIALDIVISIONThenormal reproductive method of bacteria is binaryfission, in which a singlecell1.9
9 1 Inclusions（内含物） are reserve deposits found in procaryotic and eucaryotic cells. 2 Among the inclusions found in bacteria are metachromatic granules（异染粒） (inorganic phosphate), polysaccharide granules (，多糖，usually glycogen or starch), lipid inclusions （脂滴）,sulfur granules（硫粒）, carboxysomes (，羧酶体，ribulose 1,5-diphosphate carboxylase), and gas vacuoles（气泡）. NUCLEAR AREA 1. The nuclear area contains the DNA of the bacterial chromosome. Bacteria can also contain plasmids, which are extrachromosomal DNA circles. capsule or slime layer 1. capsule（荚膜） or slime（黏液层） layer is a gelatinous polysaccharide and/or polypeptide covering. 2. Capsules may protect pathogens from phagocytosis（吞噬）. 3. Capsules provide adherence to surfaces, prevent desiccation, and may provide nutrients. FLAGELLA 1. Flagella（鞭毛） are relatively long filamentous appendages consisting of a filament, hook, and basal body. 2. Procaryotic flagella rotate to push the cell.Motile（运动）. 3. bacteria exhibit taxis（趋性）—positive taxis is movement toward an attractant and negative taxis is movement away from a repellent. FIMBRIAE AND PILIF 1. fimbriae（菌毛） and pili（性毛） are short, thin appendages. 2. Fimbriae help cells adhere to surfaces. 3. Pili join cells for the transfer of DNA from one cell to another. ENDOSPORES（芽孢） 1. Endospores are resting structures formed by some bacteria for survival during adverse environmental conditions. 2. The process of endospore formation is called sporulation; the return of an endospore to its vegetative state iscalled germination. Endospores are a method as survival, not one of reproduction. Certain bacteria will form a spore within their cell membrane (an endospore) that allows them to wait out deteriorating environmental conditions. Certain disease causing bacteria (such as the one that causes the disease Anthrax) can be virulent (capable of causing an infection) 1300 years after forming their endospore!） BACTERIAL DIVISION 1. The normal reproductive method of bacteria is binary fission, in which a single cell
divides into two identical cells2Some bacteria reproduceby budding.,aerial sporeformation, orfragmentation.binary fission (二分裂)The method by which bacteria reproduce. The circular DNA molecule isreplicated; then the cell splits into two identical cells, each containing anexact copy of theoriginal cell's DNA.ActinomycesActinomycetes(放线菌）are filamentous, gram-positive bacilli that form a branchingmyceliumCyanobacteria（蓝细菌）：Blue-green bacteria;unicellular or filamentous chains of cells that carryout photosynthesis.Rickttsias,chlamydias and mycoplasmasThe ricktsias（立克次氏体）and chlamydias（衣原体）are gram-negative obligate intracellular parasitesthat key metabolic enzymes.The ricketsias are extremely small, pleomorphic rods or cocobacilli that cannot synthessiz their own ATPMost have acomplex life-style that cyces between arthropod vectors and vertebrate hostsThe rickettsias are ususlly transmitted by tickor tick fecesThe chlamydias are small, gram-negative, pleomorphic, intracellular parasites that have nocatabolic pathways.They exist in twoforms:the elementarybody,which is theformtransmittedbetween human hosts through direct contact and body secretions, and the reticulate body,whichmultiplies intracellularly.Chlamydiatrachomatis（沙眼衣原体）istheagentof severalSTDs:NGU（nongonococcalurethritis),pelvic inflammatory disease, and lymphogranuloma venereum.It also causes oculartrachoma, a serious eyeinfectionChlamydia pneumoniae(肺炎衣原体)is the agent of respiratory infections in young adults andasthmatics.Chlamydiapsittaci（鹦鹉热衣原体）istheagentofornithosis,aninfluenza-likediseasecarriedbybirds that has serious systemic complications ifuntreated.Antibiotic therapy is usually successful.Mycoplasmas（支原体）aretinypleomorphicbacteriathatlackacell wall.Althoughmost speciesareparasitic,mycoplasmas canbe cultured on complexartificial media.They areconsideredmembrane parasites because theybind tightlyto epithelial linings of the respiratoryand urogenitaltracts.Mycoplasma pneumoniae(肺炎支原体）istheagentof primaryatypical pneumonia（walkingpneumonia).10
10 divides into two identical cells. 2. Some bacteria reproduce by budding., aerial spore formation, or fragmentation. binary fission（二分裂） The method by which bacteria reproduce. The circular DNA molecule is replicated; then the cell splits into two identical cells, each containing an exact copy of the original cell's DNA. Actinomyces Actinomycetes(放线菌) are filamentous, gram-positive bacilli that form a branching mycelium. Cyanobacteria（蓝细菌）： Blue-green bacteria;unicellular or filamentous chains of cells that carry out photosynthesis. Rickttsias , chlamydias and mycoplasmas The rickttsias（立克次氏体） and chlamydias（衣原体） are gram-negative obligate intracellular parasites that key metabolic enzymes. The rickettsias are extremely small, pleomorphic rods or coccobacilli that cannot synthessiz their own ATP. Most have a complex life-style that cyces between arthropod vectors and vertebrate hosts. The rickettsias are ususlly transmitted by tickor tick feces. The chlamydias are small, gram-negative, pleomorphic, intracellular parasites that have no catabolic pathways. They exist in two forms: the elementary body, which is the form transmitted between human hosts through direct contact and body secretions, and the reticulate body, which multiplies intracellularly. Chlamydia trachomatis（沙眼衣原体） is the agent of several STDs: NGU (nongonococcal urethritis),pelvic inflammatory disease, and lymphogranuloma venereum. It also causes ocular trachoma, a serious eye infection. Chlamydia pneumoniae(肺炎衣原体) is the agent of respiratory infections in young adults and asthmatics. Chlamydia psittaci（鹦鹉热衣原体） is the agent of ornithosis, an influenza-like disease carried by birds that has serious systemic complications if untreated. Antibiotic therapy is usually successful. Mycoplasmas（支原体）are tiny pleomorphic bacteria that lack a cell wall. Although most species are parasitic, mycoplasmas can be cultured on complex artificial media. They are considered membrane parasites because they bind tightly to epithelial linings of the respiratory and urogenital tracts. Mycoplasma pneumoniae(肺炎支原体) is the agent of primary atypical pneumonia (walking pneumonia)