Learning Objectives

By the end of this section, girlfriend will be able to do the following:

Describe the basic structure the a usual prokaryoteDescribe important differences in structure in between Archaea and also Bacteria

There are plenty of differences between prokaryotic and eukaryotic cells. The surname “prokaryote” argues that prokaryotes are characterized by exclusion—they space not eukaryotes, or organisms whose cells contain a nucleus and other internal membrane-bound organelles. However, all cells have actually four typical structures: the plasma membrane, which attributes as a obstacle for the cell and separates the cell from that environment; the cytoplasm, a complicated solution of essential molecules and salts inside the cell; a double-stranded DNA genome, the informational archive of the cell; and also ribosomes, where protein synthetic takes place. Prokaryotes come in assorted shapes, however many loss into three categories: cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped) ((Figure)).

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Common prokaryotes cell types. Prokaryotes autumn into three an easy categories based on their shape, visualized below using scanning electron microscopy: (a) cocci, or spherical (a pair is shown); (b) bacilli, or rod-shaped; and (c) spirilli, or spiral-shaped. (credit a: change of occupational by zenit Haney Carr, Dr. Richard Facklam, CDC; credit c: modification of job-related by Dr. David Cox; scale-bar data from Matt Russell)

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Recall that prokaryotes are separated into two different domains, Bacteria and Archaea, which along with Eukarya, comprise the three domains of life ((Figure)).


The three domain names of living organisms. Bacteria and also Archaea room both prokaryotes however differ sufficient to be put in different domains. One ancestor of modern-day Archaea is believed to have offered rise come Eukarya, the third domain of life. Significant groups of Archaea and also Bacteria are shown.

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Other bacter phyla. Chlamydia, Spirochetes, Cyanobacteria, and Gram-positive bacteria are explained in this table. Note that bacterial shape is not phylum-dependent; bacteria in ~ a phylum may be cocci, rod-shaped, or spiral. (credit “Chlamydia trachomatis”: modification of occupational by Dr. Lance Liotta Laboratory, NCI; credit transaction “Treponema pallidum”: alteration of job-related by Dr. David Cox, CDC; credit “Phormidium”: modification of work by USGS; credit transaction “Clostridium difficile”: change of work by Lois S. Wiggs, CDC; scale-bar data from Matt Russell)
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Archaeal phyla. Archaea space separated into 4 phyla: the Korarchaeota, Euryarchaeota, Crenarchaeota, and also Nanoarchaeota. (credit “Halobacterium”: change of occupational by NASA; credit “Nanoarchaeotum equitans”: alteration of job-related by knife O. Stetter; credit “Korarchaeota”: change of work-related by Office of science of the U.S. Dept. The Energy; scale-bar data from Matt Russell)
The Plasma Membrane that ProkaryotesThe prokaryotic plasma membrane is a thin lipid double layer (6 come 8 nanometers) that completely surrounds the cell and also separates the inside from the outside. The selectively permeable nature keeps ions, proteins, and also other molecules within the cell and also prevents them native diffusing into the extracellular environment, while various other molecules might move v the membrane. Recall that the general structure that a cabinet membrane is a phospholipid bilayer written of 2 layers the lipid molecules. In archaeal cabinet membranes, isoprene (phytanyl) chains connected to glycerol change the fat acids connected to glycerol in bacter membranes. Some archaeal membranes are lipid monolayers rather of bilayers ((Figure)).


Bacterial and archaeal phospholipids. Archaeal phospholipids different from those uncovered in Bacteria and also Eukarya in two ways. First, they have branched phytanyl sidechains instead of direct ones. Second, one ether bond instead of an ester bond connects the lipid to the glycerol.
The Cell wall of Prokaryotes

The cytoplasm of prokaryotes cells has a high concentration of liquified solutes. Therefore, the osmotic push within the cell is reasonably high. The cell wall is a safety layer that surrounds some cells and also gives lock shape and rigidity. That is located external the cabinet membrane and also prevents osmotic lysis (bursting due to increasing volume). The chemical composition the the cell wall surface varies in between Archaea and Bacteria, and additionally varies between bacterial species.

Bacterial cell wall surfaces contain peptidoglycan, written of polysaccharide chains that space cross-linked by unusual peptides include both L- and also D-amino acids consisting of D-glutamic acid and D-alanine. (Proteins typically have just L-amino acids; together a consequence, numerous of our antibiotics work by mimicking D-amino acids and also therefore have details effects on bacterial cell-wall development.) over there are an ext than 100 different forms that peptidoglycan. S-layer (surface layer) proteins are likewise present top top the outside of cell walls of both Archaea and also Bacteria.

Bacteria are divided into two major groups: Gram positive and also Gram negative, based on their reaction come Gram staining. Note that all Gram-positive bacteria belong to one phylum; bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. The Gram staining method is called after its inventor, Danish scientist Hans Christian Gram (1853–1938). The various bacterial responses come the staining procedure are ultimately due to cell wall surface structure. Gram-positive organisms generally lack the outer membrane uncovered in Gram-negative organisms ((Figure)). As much as 90 percent that the cell-wall in Gram-positive bacteria is composed of peptidoglycan, and also most that the rest is composed of acidic substances dubbed teichoic acids. Teichoic acids may be covalently connected to lipids in the plasma membrane to kind lipoteichoic acids. Lipoteichoic mountain anchor the cell wall surface to the cabinet membrane. Gram-negative bacteria have a reasonably thin cell wall composed that a few layers the peptidoglycan (only 10 percent of the total cell wall), surrounded by an outer envelope comprise lipopolysaccharides (LPS) and also lipoproteins. This outer envelope is sometimes referred to as a 2nd lipid bilayer. The chemistry the this external envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes.


Cell walls in Gram-positive and Gram-negative bacteria. Bacteria are divided into two major groups: Gram positive and also Gram negative. Both groups have a cell wall composed the peptidoglycan: in Gram-positive bacteria, the wall surface is thick, whereas in Gram-negative bacteria, the wall surface is thin. In Gram-negative bacteria, the cell wall is surrounded by an external membrane that has lipopolysaccharides and lipoproteins. Porins space proteins in this cabinet membrane that enable substances to pass v the outer membrane of Gram-negative bacteria. In Gram-positive bacteria, lipoteichoic mountain anchors the cell wall surface to the cell membrane. (credit: modification of work-related by “Franciscosp2″/Wikimedia Commons)
Which that the following statements is true?

Gram-positive bacteria have a single cell wall surface anchored come the cabinet membrane through lipoteichoic acid.Porins allow entry that substances into both Gram-positive and also Gram-negative bacteria.The cell wall surface of Gram-negative bacteria is thick, and also the cell wall of Gram-positive bacteria is thin.Gram-negative bacteria have a cell wall surface made the peptidoglycan, whereas Gram-positive bacteria have actually a cell wall surface made that lipoteichoic acid.

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Archaean cabinet walls carry out not have peptidoglycan. There are four different types of archaean cell walls. One type is composed of pseudopeptidoglycan, i m sorry is comparable to peptidoglycan in morphology but contains various sugars in the polysaccharide chain. The various other three varieties of cabinet walls space composed that polysaccharides, glycoproteins, or pure protein. Other differences between Bacteria and also Archaea room seen in (Figure). Keep in mind that functions related to DNA replication, transcription and also translation in Archaea are comparable to those checked out in eukaryotes.

Differences and Similarities between Bacteria and ArchaeaStructural CharacteristicBacteriaArchaea
Cell typeProkaryoticProkaryotic
Cell morphologyVariableVariable
Cell wallContains peptidoglycanDoes no contain peptidoglycan
Cell membrane typeLipid bilayerLipid double layer or lipid monolayer
Plasma membrane lipidsFatty acids-glycerol esterPhytanyl-glycerol ethers
ChromosomeTypically circularTypically circular
Replication originsSingleMultiple
RNA polymeraseSingleMultiple
Initiator tRNAFormyl-methionineMethionine
Streptomycin inhibitionSensitiveResistant
Calvin cycleYesNo

Reproduction

Reproduction in prokaryotes is asexual and also usually takes ar by binary fission. (Recall the the DNA of a prokaryote is a single, circular chromosome.) Prokaryotes do not experience mitosis; instead, the chromosome is replicated and also the two resulting duplicates separate from one another, as result of the growth of the cell. The prokaryote, now enlarged, is pinched inward in ~ its equator and the 2 resulting cells, which are clones, separate. Binary fission does not provide an chance for hereditary recombination or genetic diversity, but prokaryotes have the right to share gene by three other mechanisms.

In transformation, the prokaryote takes in DNA shed by other prokaryotes into its environment. If a nonpathogenic bacterium takes up DNA because that a toxin gene native a virus and incorporates the new DNA right into its own chromosome, it also may come to be pathogenic. In transduction, bacteriophages, the viruses the infect bacteria, may move brief pieces that chromosomal DNA native one bacterium to another. Transduction results in a recombinant organism. Archaea likewise have viruses that might translocate genetic material indigenous one separation, personal, instance to another. In conjugation, DNA is transferred from one prokaryote to an additional by means of a pilus, which bring the organisms into contact with one another, and provides a channel for move of DNA. The DNA transferred can be in the type of a plasmid or together a composite molecule, include both plasmid and chromosomal DNA. These three procedures of DNA exchange are presented in (Figure).

Reproduction have the right to be very rapid: a few minutes for some species. This short generation time coupled v mechanisms of genetic recombination and high prices of mutation an outcome in the rapid evolution of prokaryotes, enabling them to respond come environmental changes (such together the arrival of an antibiotic) very quickly.


Gene transfer mechanisms in prokaryotes. There room three mechanisms through which prokaryotes deserve to exchange DNA. In (a) transformation, the cabinet takes up prokaryotes DNA straight from the environment. The DNA may remain different as plasmid DNA or be integrated into the organize genome. In (b) transduction, a bacteriophage injects DNA into the cabinet that includes a little fragment the DNA indigenous a different prokaryote. In (c) conjugation, DNA is transferred from one cabinet to an additional via a adjustment bridge, or pilus, that connects the two cells after ~ the sex pilus draws the 2 bacteria close enough to form the bridge.
The advancement of ProkaryotesHow execute scientists price questions around the advancement of prokaryotes? Unlike v animals, artefacts in the fossil record of prokaryotes sell very small information. Fossils of old prokaryotes look like tiny balloon in rock. Some scientists revolve to genetics and to the principle of the molecular clock, i beg your pardon holds the the much more recently two species have diverged, the much more similar their gene (and for this reason proteins) will certainly be. Conversely, types that sail long back will have more genes that space dissimilar.

Scientists at the NASA Astrobiology Institute and at the europe Molecular Biology activities collaborated to analyze the molecular development of 32 certain proteins usual to 72 varieties of prokaryotes.1 The model they acquired from your data shows that three vital groups that bacteria—Actinobacteria, Deinococcus, and Cyanobacteria (collectively referred to as Terrabacteria by the authors)—were the an initial to colonize land. Actinobacteria room a team of really common Gram-positive bacteria that produce branched structures prefer fungal mycelia, and also include types important in decomposition of necessary wastes. You will certainly recall the Deinococcus is a genus that bacterium the is highly resistant to ionization radiation. It has a thick peptidoglycan class in addition to a 2nd external membrane, so that has attributes of both Gram-positive and Gram-negative bacteria.

Cyanobacteria are photosynthesizers, and also were most likely responsible because that the manufacturing of oxygen on the ancient earth. The timelines of aberration suggest that bacteria (members the the domain Bacteria) diverged from common ancestral species between 2.5 and also 3.2 billion years ago, vice versa, the Archaea sail earlier: in between 3.1 and 4.1 billion year ago. Eukarya later on diverged from the archaean line. The work-related further argues that stromatolites that created prior come the arrival of cyanobacteria (about 2.6 billion years ago) photosynthesized in one anoxic environment and that due to the fact that of the modifications of the Terrabacteria for land (resistance come drying and also the possession of compound that protect the organism from excess light), photosynthesis utilizing oxygen might be closely linked come adaptations to endure on land.


Section Summary

Prokaryotes (domains Archaea and also Bacteria) space single-celled organisms that absence a nucleus. They have a single piece of one DNA in the new closed area of the cell. Many prokaryotes have a cell wall surface that lies exterior the boundary of the plasma membrane. Some prokaryotes may have extr structures such together a capsule, flagella, and pili. Bacteria and also Archaea different in the lipid composition of your cell membranes and also the qualities of the cell wall. In archaeal membranes, phytanyl units, fairly than fatty acids, are linked to glycerol. Some archaeal membranes space lipid monolayers instead of bilayers.

The cell wall is located outside the cell membrane and also prevents osmotic lysis. The chemical composition the cell walls varies in between species. Bacterial cell wall surfaces contain peptidoglycan. Archaean cabinet walls execute not have actually peptidoglycan, yet they may have actually pseudopeptidoglycan, polysaccharides, glycoproteins, or protein-based cell walls. Bacteria deserve to be separated into two significant groups: Gram positive and also Gram negative, based upon the Gram stain reaction. Gram-positive organisms have a thick peptidoglycan layer strengthened with teichoic acids. Gram-negative organisms have a thin cell wall surface and an outer envelope comprise lipopolysaccharides and lipoproteins.

Prokaryotes deserve to transfer DNA from one cabinet to one more by three mechanisms: transformation (uptake of environmental DNA), transduction (transfer the genomic DNA via viruses), and also conjugation (transfer of DNA by direct cell contact).


(Figure) i m sorry of the following statements is true?

Gram-positive bacteria have actually a solitary cell wall surface anchored come the cabinet membrane by lipoteichoic acid.Porins allow entry that substances into both Gram-positive and Gram-negative bacteria.The cell wall of Gram-negative bacteria is thick, and also the cell wall of Gram-positive bacteria is thin.Gram-negative bacteria have actually a cell wall made that peptidoglycan, conversely, Gram-positive bacteria have a cell wall made of lipoteichoic acid.

The visibility of a membrane-enclosed cell nucleus is a properties of ________.

prokaryotic cellseukaryotic cellsall cellsviruses

Which that the following consist of prokaryotic cells?

bacteria and also fungiarchaea and also fungiprotists and also animalsbacteria and archaea

The cell wall is ________.

interior come the cabinet membraneexterior to the cabinet membranea component of the cabinet membraneinterior or exterior, depending upon the certain cell

B


Organisms most likely to be discovered in extreme settings are ________.

fungibacteriavirusesarchaea

B


Prokaryotes stain together Gram-positive or Gram-negative due to the fact that of distinctions in the cabinet _______.

wallcytoplasmnucleuschromosome

Pseudopeptidoglycan is a properties of the wall surfaces of ________.

eukaryotic cellsbacterial prokaryotes cellsarchaean prokaryotic cellsbacterial and also archaean prokaryotic cells

The lipopolysaccharide layer (LPS) is a characteristic of the wall surface of ________.

archaean cellsGram-negative bacteriabacterial prokaryotes cellseukaryotic cells

B


Critical reasoning Questions


Mention 3 differences in between bacteria and also archaea.


Responses will certainly vary. A feasible answer is: Bacteria contain peptidoglycan in the cell wall; archaea perform not. The cabinet membrane in bacteria is a lipid bilayer; in archaea, it can be a lipid bilayer or a monolayer. Bacteria contain fatty acids on the cabinet membrane, conversely, archaea save phytanyl.


Explain the statement that both types, bacteria and archaea, have actually the same basic structures, but developed from various chemical components.

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Both bacteria and archaea have actually cell membranes and also they both save on computer a hydrophobic portion. In the situation of bacteria, that is a fatty acid; in the case of archaea, the is a hydrocarbon (phytanyl). Both bacteria and archaea have a cell wall surface that protects them. In the situation of bacteria, that is composed of peptidoglycan, conversely, in the instance of archaea, it is pseudopeptidoglycan, polysaccharides, glycoproteins, or pure protein. Bacterial and archaeal flagella likewise differ in your chemical structure.


A scientist isolates a brand-new species of prokaryote. That notes the the specimen is a bacillus through a lipid bilayer and also cell wall surface that stains positive for peptidoglycan. Its circular chromosome replicates indigenous a single origin that replication. Is the specimen most most likely an Archaea, a Gram-positive bacterium, or a Gram-negative bacterium? exactly how do you know?


The specimen is most likely a gram-positive bacterium. Since the cell wall contains peptidoglycan and also the chromosome has actually one origin of replication, we have the right to conclude that the specimen is in the Domain Bacteria. Due to the fact that the gram stain detects peptidoglycan, the prokaryote is a gram-positive bacterium.


Glossary

capsuleexternal framework that permits a prokaryote to attach to surfaces and also protects it from dehydrationconjugationprocess through which prokaryotes move DNA from one individual to one more using a pilusGram negativebacterium who cell wall contains little peptidoglycan yet has an outer membraneGram positivebacterium that contains mainly peptidoglycan in its cabinet wallspeptidoglycanmaterial written of polysaccharide chain cross-linked to unexplained peptidespilussurface appendage of part prokaryotes used for attachment to surfaces including other prokaryotespseudopeptidoglycancomponent the archaea cell walls that is comparable to peptidoglycan in morphology yet contains different sugarsS-layersurface-layer protein existing on the outside of cell walls of archaea and bacteriateichoic acidpolymer associated with the cell wall of Gram-positive bacteriatransductionprocess through which a bacteriophage move DNA from one prokaryote to anothertransformationprocess through which a prokaryote takes in DNA discovered in its environment that is shed by various other prokaryotes