In part because of these physical constrains, during their evolution, the much larger eukaryotic cells have become compartmentalized.
Giant prokaryotic cells are rare exceptions but they are now known to exist Prescott et al. Epulopiscium spp. It will be interesting to discover how this giant bacterium has solved the problems that are likely to be created by a large volume of cytosol to be contained by external envelopes only.
For example, one of the fundamental distinguishing characteristics of an eukaryotic cell is the organization of its DNA in separate chromosomes contained in a membrane-enclosed bag, the nucleus.
This feature does not exist in prokaryotic cells Fig. However, several different prokaryotic cells contain intracellular membranes or sac-like membrane components that can be more or less numerous or complicated in arrangement.
Their functions vary from one kind of bacterium to another. For example, the cyanobacteria have thylakoids containing chlorophyll and capable of photosynthesis. All nitrogen-fixers have lamellae. For a discussion of inclusions and intracellular membranes, the reader is referred to the many excellent papers on the subject, for example, Jensen In the present chapter, we will discuss, in very general terms, the main structure of the prokaryotic cell, some of the molecular but mostly the structural aspects that differentiate the prokaryotic cellular body from its eukaryotic counterpart.
We will hereafter refer to it as the large replicon. Also present are from one to seventeen Fox, much smaller replicons circular DNA molecules which the cell harbours on a temporary basis Fig. Their copies are able to move from one strain to another Fig. These small replicons act as visiting genetic information molecules, easily exchangeable groups of genes, playing a major role in the solidarity of prokaryotes through a global communication System Sonea, Many of them also possess one or several flagellar structures that enable them to move.
Bacterial flagella often move by rotation imparted from a basal body, a motor-like structure moved by protons. Other protruding filamentous proteinic structures that are not essential in all conditions are fimbriae and pili. Fimbriae seem to be involved in the sticking adherence of the cells that produce them to inert surface or animal tissues e. Flagella, fimbriae and pili cannot be visualized under the ordinary light microscope without a special treatment and are not produced under all conditions.
It is very significant that all prokaryotic strains studied until now possess surface receptors for temperate bacteriophages, and that about half of the strains also have receptors for self-replicating plasmids Fig. The generalized presence of such receptors for exchangeable genetic information is additionnal proof of the importance of the genetic communication System in prokaryotes.
Finally, many prokaryotic organisms secrete on their surface slimy materials often referred to as slime layers, capsules or, to use the more general term, glycocalyx.
We will return to these in later pages. As noted previously, in prokaryotes mechanical resistance is conferred by the outer layer of the envelope: the cell wall. Basically, only three major specific shapes are adopted by prokaryotic cells and this fact too lends support to the concept of a unified prokaryotic world.
These shapes have been recognized ever since the earliest times of examination with the ordinary light microscope Fig. The cross-links in P. It is present in eubacteria and its sugar derivative, N-acetylmuramic acid, has never been found in the cell membranes of eukaryotes. A variety of different types of P. In Gram-negative bacteria, only between 10 to 15 per cent of the wall is P. They are important in the diffusion of nutrients and other substances. Other proteins present in the envelopes and whose presence and concentrations depend on the milieu and the growing conditions play a role in the entry of DNA during gene exchange processes.
Lipopolysaccharides play important roles in the physical interactions e. It is beyond the scope of this book to review the biochemistry of peptidoglycan formation but it is important to recall that the assembly of its basic constituent molecules synthesized in the cell and organized in a network outside the cytoplasm requires several different biochemical reactions related to transport through the cytoplasmic membrane and insertion into the existing web.
Some of the steps involved in the transport of these basic units and in the cross-linking between adjacent glycan chains can be inhibited by several antibiotics, of which penicillins beta-lactams and cephalosporins are of particular chemotherapeutic importance.
Also, the P. These enzymes are useful, non-specific protective agents against bacterial infections and are also used extensively in the laboratory in experimental transformation and the production of cell-wall free bacteria protoplasts and spheroplasts.
Under natural conditions a bacterium that cannot keep its P. Antibiotics that interfere with the synthesis of the P. In addition to penicillins and cephalosporins, a group of substances called the glycopeptide antibiotics e.
Acquisition of resistance to vancomycin results from the transfer of resistance genes able to move from one strain to another by common gene exchange processes transfection, mobilization and transduction so that the ability to produce protective protein and resist the lethal effects of glycopeptide antibiotics can easily disseminate from one strain to another Arthur et al. The increased use of vancomycin in humans and of avoparcin as a growth promoter for farm animals is certainly a cause for justified concern since it could end up in an increased transfer of resistance genes to a large number of different pathogenic bacterial strains.
Archaea and chlamydia do not have it. However, their walls may contain a heteropolymer somewhat similar to peptidoglycan that lacks muramic acid and is called a pseudopeptidoglycan or, in the case of certain Archaea, be made of special proteins. Many Archaea are found in extreme conditions of temperature or salinity and it is not surprising that they have evolved surface layers different from those of the eubacteria.
For example, bacterial lipopoly-saccharides LPS, also called endotoxins, are well known to activate macrophages in animals and to generate immunoregulatory substances e. Their role in the triggering and the stimulation of the immune response receives considerable attention and is investigated in many laboratories. They are now considered as modulins or modulators of many of the immune reactions and as mediators of homeostasis and, in large concentrations, of tissue pathology Henderson et al, This is also true of peptidoglycan which should not be viewed merely as a biologically inert corset that determines cell shape.
Fragments of PG are potent biological effectors which modulate a remarkably diverse set of inflammatory and immune reactions in animals. A currently accepted model for the structure of the bacterial membrane is the fluid mosaic model of Singer and Nicholson. Although it appears simple, the membrane fulfills several functions and can be considered a multipurpose organ. There are no mitochondria in a prokaryotic cell and the role of this eukaryotic energy generator respiration and electron transport is assumed by the membrane.
It also acts as a boundary layer for the cytosol and as such it pumps metabolites in and catabolites out of the cell and probably plays an essential role in the equal and symmetric genome distribution before separation of the mother cell into two identical daughters.
The phospholipid leaflets are arranged in a bilayer structure into which various and numerous proteins are inserted. They play different roles, some of which are enumerated above electron transport, active transport of metabolites, catabolites, DNA, etc. Bacterial membranes differ, on the one hand, from the eukaryotic cell membrane and they may also differ among strains both in the occurrence and nature of their basic constituents, the fatty acids.
Another way in which bacterial membranes usually differ from eukaryotic ones is in lacking sterols such as cholesterol. However, many prokaryotic membranes contain sterol-like molecules that are synthesized from the same precursors as steroids. They are called hopanoids and they probably stabilize the two fatty acid sheets. Hopanoids can be isolated from kerosene, an organic precursor of petroleum. It is present in large quantities in some sediments.
In fact, it has been estimated that the total mass of hopanoids in all sediments may be around 10 tons, about as much as the total mass of organic carbon in all living organisms 10 12 tons Prescott et al, Since in all probability these hopanoids are of prokaryotic origin, this shows the enormous importance of prokaryotes in the formation of fossil fuel, in particular petroleum.
However, horizontal genetic exchanges are possible despite these differences. Some may appear randomly distributed, others equally spaced. Ribosomes in both prokaryotes and eukaryotes are an essential part of the translation in the synthesis of proteins machinery in cells.
They act as the physical support on which the genetic information already transferred from the DNA to the messenger RNA is used to assemble amino acids in the correct order to make functional proteins. In bacteria, ribosomes are smaller than in eukaryotic cells. They sediment less easily in the ultracentrifuge. They consist of about two-thirds ribonucleic acid and one-third protein and, following proper Chemical treatment, they dissociate into two subunits of different size and weight.
To fulfill their roles in protein biosynthesis, ribosomal RNA molecules must contain several functionally different regions. The nucleotide sequences in some of these regions are conserved and in others are highly varied. The smaller subunit of the prokaryotic ribosome contains a sequence 16S approximately nucleotides that is particularly suitable for genetic and phylogenetic comparison between different bacterial strains and also for studies of evolution.
During the very long geologic eons, when bacteria evolved into what taxonomists traditionnally call groups, families, genera or species, changes were imprinted in the sequence of ribosomal RNAs.
These imprints or molecular signatures can be used to identify different bacteria and also to assess the most probable evolutionary distance between them Woese, Chloramphenicol, streptomycin, erythromycin and tetracyclines, for example, act as much more potent protein synthesis inhibitors in bacteria than in eukaryotic cells and are clinically useful antibacterial drugs although they are not entirely devoid of toxicity in eukaryotes.
Laboratory techniques can be used to stain the bodies of the bacterial cells with a cationic dye e. India ink. It can be visualized as a defined area surrounding blue dots bacterial bodies. These transparent zones are usually called capsules and our knowledge of their chemistry is now extensive Bayer and Bayer, A large number of polysaccharides have been isolated from capsules and the slime material of bacteria.
Size, charge and composition of the capsular material are of primary importance in determining the roles and the usefulness of this structure for the bacteria. It seems that capsular material can be involved in giving some pathogenic bacteria a certain protection against phagocytosis by mononuclear cells of the animal body, and also in sticking adherence to the surfaces of the environment.
Capsule-producing bacteria such as Streptococcus pneumoniae and Klebsiella pneumoniae are more resistant to phagocytic white blood cells and can invade a tissue or an organ more rapidly than those deprived of capsules.
The immune response to polysaccharidic capsular material is often less pronounced and also affords shorter protection than proteinic substances of bacterial origin. They have a very high water content and they too seem to facilitate the attachment of the bacterial cells to solid surfaces. The sticky polysaccharide of the glycocalyx allows some oral bacteria to attach to tooth enamel and plays a role in the formation of dental plaque, the initial phase of tooth decay. Polysaccharides excreted by other types of bacteria e.
Xanthomonas, Pseudomonas find many applications as gelifying agents in shampoos, seasonings, lubricating agents, etc. As noted previously, there is at least one small replicon in each prokaryotic cell and, in some cases, up to seventeen Fox, a.
Borrelia burgdorferi a much larger proportion of the hereditary information may be found among the plasmids than was thought initially Fox, b.
Also, it is now known that a few types of bacteria have a different distribution of their genes: two circular large replicons or even a linear one Jumas-Bilak et al. The similarity of the general genetic organization one large replicon and a variable stock of small replicons-associated genes across the entire prokaryotic super-kingdom after 3. It lends further support to our view that the prokaryotic world is organized as a global superorganism whose constituent cells communicate and cooperate through easy and frequent genetic exchanges, with similar mechanisms and structures.
Contrary to what we observe in eukaryotes, the free circulation of genes in prokaryotes is not compatible with the notion of species. Bacillus and Clostridium and mostly under adverse conditions, specialized and extremely resistant cells are formed. They are called spores or endospores, have no metabolic activity of their own are fully dormant , but can be converted into vegetative growing and multiplying cells if favorable conditions prevail.
This process is called germination. Various enzymes in spores are much more stable, particularly in relation to heat, than the corresponding enzymes in vegetative cells. The resistance of these prokaryotic endospores to elevated temperatures, to chemical substances and to radiations is much higher than that of any eukaryotic cell.
It appears that this striking molecular stability depends more on the internal environment of the sporulated cell than on intrinsic structural or other peculiar properties. Calcium dipicolinate stabilizes the DNA helices of the spores.
Dehydration, calcium dipicolinate and an impervious, bilayered protein keratin-like coat all appear to play major roles in protecting the prokaryotic spore.
The distinct organization of the intracellular genome in practicaily all prokaryotic cells. E: Equator LR: The large replicon, also called genophore, nucleoid, and, erroneously, chromosome.
It represents the large majority of the cellular DNA, containing the essential and stable genes of prokaryotic cells. SR: Small replicon plasmids and prophages. Very small, self-replicating DNA molecules kept ususally as long as the few converting genes they carry are useful to their host cell.
Easily disposable and replaceable by other SR carrying temporarily better genetic supplements. There is at least one SR per prokaryotic cell but their number may reach seventeen. SR are visiting genes, each one able to multiply in many different prokaryotic strains. It can last almost forever as demonstrated by spores kept in glass containers sealed about years ago, and even more strikingly by Bacillus spores isolated from the gut of extinct bees, fossilized in amber, which apparently have been reactivated after several million years Cano, ; These communities are opportunistically rearranged and reorganized when necessary.
Each type of cell is highly specialized, nonetheless it can fit well with others in metabolically complementary ensembles similar to the ones of a multicellular eukaryotic organism animal or plant. However, they have the ability to modify or replace constituent cells if needed. These cells practice an efficient sharing of their biochemical activities: exchange of partially modified substances, of enzymes, cross-feeding with metabolic end-products, etc. Such teams form giant ensembles in all fertile soils, ocean floors, the digestive tracts of all animals, etc.
Abundant populations can also be found at the surface of naturel waters. Sometimes these cells originate from far-away communities. As is the case for artistic mosaics, the smaller and more varied the stones, the easier it is to obtain a good result; in prokaryotic mixed communities, the cells fall rapidly in their respective, appropriate place. In some cases it is amazing how rapidly new, well-balanced and successful communities of prokaryotic strains become established and persist practically unchanged for long periods of time.
In the sterile digestive tract of any newborn animal a prokaryotic community will form, sometimes within a few days, and maintain a surprising resilience during the entire life-time of its host. In such communities, different strains do not kill their local competitors but they eventually outbreed the less efficient and poorly adapted ones. Nevertheless, biological solidarity and interdependance among the stable strains in these communities is enormous.
In some cases less than one per cent of the strains from well established mixed groups can be grown when artificially isolated and fed in the laboratory. This shows that team partners offer each other support and assistance in the form of substances that we either fail to identify as growth or multiplication requirements or to supply in proper concentrations in laboratory culture media.
There are unsuspected similarities between the ways of functioning of our blood cells and those of prokaryotic cells. Both belong to their own multicellular organism and proceed from a common original cell egg for animals or first viable cell on earth for prokaryotes , they move freely in their liquid or viscous surroundings, have areas of high biochemical specialization and provide services and help e.
They too are so adapted and specialized for life in a multicellular organism that most of them cannot be easily cultivated as isolated cells in vitro. Interestingly, some bacterial teams create their own microclimate adjusted to their need. Sometimes, even the temperature is locally maintained at an optimal level. The compounded effects of prokaryotic communities play a major role in stabilizing the atmospheric nitrogen concentration, the acidity and alkalinity of their environment, etc.
This ensures favorable conditions and homeostasis for the entire planet. The significance and importance of prokaryotes as essential components and stabilizers of the biosphere cannot be overemphasized. The totality of their local mixed communities, acting as an ensemble, a single global superorganism, represents the most active and decisive element in the maintenance of planetary homeostasis. Soil fertility and its conservation depend mostly on large, mixed prokaryotic communities, often working in unison with fungi.
This activity is one of the most evident confirmations of the Gaia hypothesis Lovelock and Margulis, which presents the entire biosphere as a life-supporting entity, modified and maintained in a form most favorable to life, just as an animal maintains a stable internal environment favorable to all its cells: homeostasis. The latter has been created for our biosphere and improved by prokaryotes alone over the first two billion years of life on our planet.
As he gradually acquired a better understanding of the prokaryotes, man has recently begun to copy and exploit this potential of prokaryotic communities in sewage treatment, sludge digestion processes and oil spill clean-ups, etc. Learning Objectives Describe the structure of prokaryotic cells. Key Points Prokaryotes lack an organized nucleus and other membrane-bound organelles. Prokaryotic DNA is found in a central part of the cell called the nucleoid.
The cell wall of a prokaryote acts as an extra layer of protection, helps maintain cell shape, and prevents dehydration. Prokaryotic cell size ranges from 0. The small size of prokaryotes allows quick entry and diffusion of ions and molecules to other parts of the cell while also allowing fast removal of waste products out of the cell. Key Terms eukaryotic : Having complex cells in which the genetic material is organized into membrane-bound nuclei. All prokaryotes have chromosomal DNA localized in a nucleoid, ribosomes, a cell membrane, and a cell wall.
The other structures shown are present in some, but not all, bacteria. Cell Size At 0. The cell on the left has a volume of 1 mm3 and a surface area of 6 mm2, with a surface area-to-volume ratio of 6 to 1, whereas the cell on the right has a volume of 8 mm3 and a surface area of 24 mm2, with a surface area-to-volume ratio of 3 to 1.
Provided by : Boundless. Structurally, peptidoglycan resembles a layer of meshwork or fabric Figure 3. The structure of the long chains has significant two-dimensional tensile strength due to the formation of peptide bridges that connect NAG and NAM within each peptidoglycan layer. In gram-negative bacteria, tetrapeptide chains extending from each NAM unit are directly cross-linked, whereas in gram-positive bacteria, these tetrapeptide chains are linked by pentaglycine cross-bridges.
Peptidoglycan subunits are made inside of the bacterial cell and then exported and assembled in layers, giving the cell its shape.
Since peptidoglycan is unique to bacteria, many antibiotic drugs are designed to interfere with peptidoglycan synthesis, weakening the cell wall and making bacterial cells more susceptible to the effects of osmotic pressure see Mechanisms of Antibacterial Drugs.
The Gram staining protocol see Staining Microscopic Specimens is used to differentiate two common types of cell wall structures Figure 3. Gram-positive cells have a cell wall consisting of many layers of peptidoglycan totalling 30— nm in thickness. These peptidoglycan layers are commonly embedded with teichoic acids TAs , carbohydrate chains that extend through and beyond the peptidoglycan layer.
TA also plays a role in the ability of pathogenic gram-positive bacteria such as Streptococcus to bind to certain proteins on the surface of host cells, enhancing their ability to cause infection. In addition to peptidoglycan and TAs, bacteria of the family Mycobacteriaceae have an external layer of waxy mycolic acids in their cell wall; as described in Staining Microscopic Specimens , these bacteria are referred to as acid-fast, since acid-fast stains must be used to penetrate the mycolic acid layer for purposes of microscopy Figure 3.
Gram-negative cells have a much thinner layer of peptidoglycan no more than about 4 nm thick [5] than gram-positive cells , and the overall structure of their cell envelope is more complex. In gram-negative cells , a gel-like matrix occupies the periplasmic space between the cell wall and the plasma membrane, and there is a second lipid bilayer called the outer membrane, which is external to the peptidoglycan layer Figure 3.
This outer membrane is attached to the peptidoglycan by murein lipoprotein. The outer leaflet of the outer membrane contains the molecule lipopolysaccharide LPS , which functions as an endotoxin in infections involving gram-negative bacteria, contributing to symptoms such as fever, hemorrhaging, and septic shock.
The composition of the O side chain varies between different species and strains of bacteria. These O side chains are also called O-antigens and can be detected using serological or immunological tests to identify specific pathogenic strains: for example, Escherichia coli OH7 , a deadly strain of bacteria that causes bloody diarrhoea and kidney failure, expresses the O O-antigen as well as the H7 flagellar antigen see discussion on Flagella, below.
Archaeal cell wall structure differs from that of bacteria in several significant ways. First, archaeal cell walls do not contain peptidoglycan; instead, they contain a similar polymer called pseudopeptidoglycan pseudomurein in which NAM is replaced with a different subunit. Other archaea may have a layer of glycoproteins or polysaccharides that serves as the cell wall instead of pseudopeptidoglycan. Last, as is the case with some bacterial species, there are a few archaea that appear to lack cell walls entirely.
Although most prokaryotic cells have cell walls, some may have additional cell envelope structures exterior to the cell wall, such as glycocalyces and S-layers. A glycocalyx is a sugar coat, of which there are two important types: capsules and slime layers also called E xtracellular P oly s accharide or EPS. A capsular polysaccharide layer is an organized layer located outside of the cell wall Figure 3. A slime layer is a less tightly organized layer that is only loosely attached to the cell wall and can be more easily washed off.
Glycocalyces allow cells to adhere to surfaces, aiding in the formation of biofilms colonies of microbes that form in layers on surfaces. In nature, most microbes live in mixed communities within biofilms , partly because the biofilm affords them some level of protection. Capsular and EPS layers and biofilms hold water like a sponge, preventing desiccation. They also protect cells from predation and hinder the action of antibiotics, disinfectants and host immune responses.
All of these properties are advantageous to the microbes, but they present challenges in a clinical setting, where the goal is often to eliminate microbes. As explained in Staining Microscopic specimens , capsules are difficult to stain for microscopy; negative staining techniques are typically used.
Like the LPS O side chains, capsules are antigenic, and can be used to help identify specific pathogenic strains of bacteria. The capsule is the primary virulence factor in this pathogen. An S-layer is another type of cell envelope structure; it is composed of a mixture of structural proteins and glycoproteins. In bacteria, S-layers are found outside the cell wall, but in some archaea, the S-layer serves as the cell wall. The exact function of S-layers is not entirely understood, and they are difficult to study; but available evidence suggests that they may play a variety of functions in different prokaryotic cells, such as helping the cell withstand osmotic pressure and, for certain pathogens, interacting with the host immune system.
After diagnosing Barbara with pneumonia, the PA writes her a prescription for amoxicillin, a commonly-prescribed type of penicillin derivative. More than a week later, despite taking the full course as directed, Barbara still feels weak and is not fully recovered, although she is still able to get through her daily activities.
She returns to the health centre for a follow-up visit. Many types of bacteria, fungi, and viruses can cause pneumonia. Amoxicillin targets the peptidoglycan of bacterial cell walls.
Another possibility is that the pathogen is a bacterium containing peptidoglycan but has developed resistance to amoxicillin. Jump to the next Clinical Focus box. Go back to the previous Clinical Focus box.
Many bacterial cells have protein appendages embedded within their cell envelopes that extend outward, allowing interaction with the environment. These appendages can attach to other surfaces, transfer DNA, or provide movement.
Filamentous appendages include fimbriae, pili, and flagella. Fimbriae and pili are structurally similar and, because differentiation between the two is problematic, these terms are often used interchangeably. Fimbriae enable a cell to attach to surfaces and to other cells. For pathogenic bacteria, adherence to host cells is important for colonization, infectivity, and virulence. Adherence to surfaces is also important in biofilm formation.
The term pili singular: pilus commonly refers to longer, less numerous protein appendages that aid in attachment to surfaces Figure 3. A specific type of pilus, called the F pilus or sex pilus, is important in the transfer of DNA between bacterial cells, which occurs between members of the same generation when two cells physically transfer or exchange parts of their respective genomes see How Asexual Prokaryotes Achieve Genetic Diversity.
Before the structure and function of the various components of the bacterial cell envelope were well understood, scientists were already using cell envelope characteristics to classify bacteria. In doing so, Lancefield discovered that one group of S. She determined that various strains of Group A strep could be distinguished from each other based on variations in specific cell surface proteins that she named M proteins.
Today, more than 80 different strains of Group A strep have been identified based on M proteins. Various strains of Group A strep are associated with a wide variety of human infections, including streptococcal pharyngitis strep throat , impetigo , toxic shock syndrome , scarlet fever , rheumatic fever , and necrotizing fasciitis. The M protein is an important virulence factor for Group A strep, helping these strains evade the immune system.
Changes in M proteins appear to alter the infectivity of a particular strain of Group A strep. Flagella are structures used by cells to move in aqueous environments. Bacterial flagella act like propellers. They are stiff spiral filaments composed of flagellin protein subunits that extend outward from the cell and spin in solution. The basal body is the motor for the flagellum and is embedded in the plasma membrane Figure 3.
A hook region connects the basal body to the filament. Gram-positive and gram-negative bacteria have different basal body configurations due to differences in cell wall structure.
Different types of motile bacteria exhibit different arrangements of flagella Figure 3. A bacterium with a singular flagellum, typically located at one end of the cell polar , is said to have a monotrichous flagellum. An example of a monotrichously flagellated bacterial pathogen is Vibrio cholerae , the gram-negative bacterium that causes cholera. Cells with amphitrichous flagella have a flagellum or tufts of flagella at each end. An example is Spirillum minor , the cause of spirillary Asian rat-bite fever or sodoku.
Cells with lophotrichous flagella have a tuft at one end of the cell. Flagella that cover the entire surface of a bacterial cell are called peritrichous flagella. The gram-negative bacterium E. Because of their exposed position on the surface of cells, like the LPS O side chains, these are antigenic and can be used to help identify specific pathogenic strains, for example E.
Different species move in response to a different environmental signals, including light phototaxis , magnetic fields magnetotaxis using magnetosomes, and, most commonly, chemical gradients chemotaxis. When running, flagella rotate in a counterclockwise direction, allowing the bacterial cell to move forward. In a peritrichous bacterium, the flagella are all bundled together in a very streamlined way Figure 3.
When tumbling, flagella are splayed out while rotating in a clockwise direction, creating a looping motion so that cells move based on the effects of gravity and brownian motion. The cell then begins to swim in whatever direction it points when the run begins, meaning the directions of the runs are random, but the duration of those runs is not.
When an attractant exists, runs and tumbles still occur but the length of runs is longer, while the length of the tumbles is reduced, allowing overall movement toward the higher concentration of the attractant. When no chemical gradient exists, the lengths of runs and tumbles are more equal, and overall movement is more random Figure 3.
Skip to content 3. The Cell. Explain the difference between cell morphology and arrangement. What advantages do cell walls provide prokaryotic cells? What is an inclusion? What is the function of an endospore? What form of treatment should the PA prescribe, given that the amoxicillin was ineffective?
What is the peptidoglycan layer and how does it differ between gram-positive and gram-negative bacteria? Compare and contrast monotrichous, amphitrichous, lophotrichous, and peritrichous flagella.
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