Learning Objectives

By the finish of this section, friend will be able to do the following:

Describe the an easy structure that a common prokaryoteDescribe important differences in structure between Archaea and also Bacteria

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

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Common prokaryotic cell types. Prokaryotes loss into three straightforward categories based upon 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: alteration of job-related by janice Haney Carr, Dr. Richard Facklam, CDC; credit c: alteration of work by Dr. David Cox; scale-bar data from Matt Russell)

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Recall that prokaryotes are divided into two different domains, Bacteria and also Archaea, which in addition to Eukarya, comprise the three domain names of life ((Figure)).


The three domains of living organisms. Bacteria and Archaea space both prokaryotes however differ sufficient to be placed in separate domains. One ancestor of modern Archaea is thought to have provided rise come Eukarya, the third domain of life. Major groups of Archaea and Bacteria room shown.

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


Bacterial and archaeal phospholipids. Archaeal phospholipids differ from those found in Bacteria and Eukarya in two ways. First, they have actually branched phytanyl sidechains rather of straight ones. Second, an ether bond instead of one ester bond connects the lipid come the glycerol.
The Cell wall of Prokaryotes

The cytoplasm of prokaryotic cells has a high concentration of liquified solutes. Therefore, the osmotic pressure within the cell is reasonably high. The cell wall is a security layer that surrounds part cells and gives castle shape and rigidity. It is located outside the cell membrane and prevents osmotic lysis (bursting due to increasing volume). The chemical composition that the cell wall surface varies in between Archaea and Bacteria, and additionally varies between bacterial species.

Bacterial cell wall surfaces contain peptidoglycan, composed of polysaccharide chains that space cross-linked by unexplained peptides comprise both L- and D-amino acids consisting of D-glutamic acid and also D-alanine. (Proteins typically have only L-amino acids; together a consequence, plenty of of our antibiotics work-related by mimicking D-amino acids and also therefore have specific effects on bacter cell-wall development.) over there are more than 100 various forms the peptidoglycan. S-layer (surface layer) proteins are also present on the external of cell wall surfaces of both Archaea and also Bacteria.

Bacteria are split into two major groups: Gram positive and also Gram negative, based on their reaction come Gram staining. Note that all Gram-positive bacteria belong come one phylum; bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. The Gram staining an approach is called after that inventor, Danish scientist Hans Christian Gram (1853–1938). The different bacterial responses come the staining procedure space ultimately due to cell wall surface structure. Gram-positive organisms frequently lack the external membrane discovered in Gram-negative organisms ((Figure)). As much as 90 percent that the cell-wall in Gram-positive bacteria is written of peptidoglycan, and also most of the remainder is created of acidic substances called teichoic acids. Teichoic acids might be covalently linked to lipids in the plasma membrane to form lipoteichoic acids. Lipoteichoic mountain anchor the cell wall to the cell membrane. Gram-negative bacteria have actually a reasonably thin cell wall composed of a couple of layers that peptidoglycan (only 10 percent the the total cell wall), surrounding by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. This outer envelope is occasionally referred to as a second lipid bilayer. The chemistry of this outer envelope is very different, however, from the of the typical lipid double layer that forms plasma membranes.


Cell wall surfaces in Gram-positive and also Gram-negative bacteria. Bacteria are split into two significant groups: Gram positive and also Gram negative. Both groups have a cell wall surface composed of peptidoglycan: in Gram-positive bacteria, the wall surface is thick, conversely, in Gram-negative bacteria, the wall surface is thin. In Gram-negative bacteria, the cell wall surface is surrounded by an outer membrane that contains lipopolysaccharides and lipoproteins. Porins are proteins in this cabinet membrane that permit substances come pass through the outer membrane the Gram-negative bacteria. In Gram-positive bacteria, lipoteichoic acid anchors the cell wall surface to the cabinet membrane. (credit: change of work by “Franciscosp2″/Wikimedia Commons)
Which of the complying with statements is true?

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

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Archaean cell walls execute not have actually peptidoglycan. Over there are four different varieties of archaean cabinet walls. One kind is created of pseudopeptidoglycan, i m sorry is similar to peptidoglycan in morphology however contains different sugars in the polysaccharide chain. The various other three species of cell walls room composed of polysaccharides, glycoproteins, or pure protein. Other differences between Bacteria and also Archaea space seen in (Figure). Keep in mind that attributes related to DNA replication, transcription and 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 location by binary fission. (Recall the the DNA of a prokaryote is a single, one chromosome.) Prokaryotes execute not experience mitosis; instead, the chromosome is replicated and the two resulting duplicates separate from one another, because of the development of the cell. The prokaryote, currently enlarged, is pinched inward in ~ its equator and also the 2 resulting cells, which are clones, separate. Binary fission go not administer an possibility for hereditary recombination or genetic diversity, but prokaryotes can share genes by three various other mechanisms.

In transformation, the prokaryote absorbs DNA burned by various other prokaryotes into its environment. If a nonpathogenic bacter takes increase DNA because that a toxin gene native a pathogen and incorporates the brand-new DNA into its own chromosome, it also may become pathogenic. In transduction, bacteriophages, the viruses that infect bacteria, might move brief pieces the chromosomal DNA native one bacterium to another. Transduction outcomes in a recombinant organism. Archaea additionally have viruses that may translocate genetic material indigenous one individual to another. In conjugation, DNA is moved from one prokaryote to an additional by means of a pilus, which brings the organisms into contact with one another, and also provides a channel for transfer of DNA. The DNA transferred deserve to be in the type of a plasmid or together a composite molecule, include both plasmid and also chromosomal DNA. This three processes of DNA exchange are displayed in (Figure).

Reproduction can be an extremely rapid: a couple of minutes for some species. This short generation time coupled v mechanisms of genetic recombination and high prices of mutation an outcome in the rapid development of prokaryotes, permitting them to respond come environmental transforms (such together the introduction of one antibiotic) really quickly.


Gene carry mechanisms in prokaryotes. There are three mechanisms by which prokaryotes deserve to exchange DNA. In (a) transformation, the cabinet takes up prokaryotes DNA directly from the environment. The DNA might remain different as plasmid DNA or be included into the organize genome. In (b) transduction, a bacteriophage injects DNA into the cell that has a tiny fragment of DNA indigenous a different prokaryote. In (c) conjugation, DNA is moved from one cabinet to another via a mating bridge, or pilus, the connects the two cells after the sex pilus paint, etc the two bacteria close sufficient to kind the bridge.
The advancement of ProkaryotesHow perform scientists answer questions about the evolution of prokaryotes? Unlike with animals, artefacts in the fossil record of prokaryotes sell very little information. Fossils of old prokaryotes look prefer tiny bubbles in rock. Some scientists turn 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 an ext similar their gene (and therefore proteins) will certainly be. Conversely, types that sail long ago will have more genes that are dissimilar.

Scientists at the NASA Astrobiology Institute and at the european Molecular Biology activities collaborated to analysis the molecular advancement of 32 particular proteins common to 72 types of prokaryotes.1 The version they derived from their data indicates that three necessary groups the bacteria—Actinobacteria, Deinococcus, and Cyanobacteria (collectively dubbed Terrabacteria through the authors)—were the an initial to colonize land. Actinobacteria room a group of very common Gram-positive bacteria that produce branched structures choose fungal mycelia, and include types important in decomposition of essential wastes. You will certainly recall that Deinococcus is a genus the bacterium that is highly resistant to ionization radiation. It has a special peptidoglycan class in enhancement to a second external membrane, so that has functions of both Gram-positive and Gram-negative bacteria.

Cyanobacteria space photosynthesizers, and also were most likely responsible because that the production of oxygen on the old earth. The timelines of divergence suggest the bacteria (members that the domain Bacteria) sail from common ancestral varieties between 2.5 and also 3.2 billion years ago, conversely, the Archaea diverged earlier: between 3.1 and 4.1 billion years ago. Eukarya later on diverged from the archaean line. The job-related further suggests that stromatolites that formed prior to the arrival of cyanobacteria (about 2.6 billion year ago) photosynthesized in one anoxic environment and that because of the adjustments of the Terrabacteria because that land (resistance to drying and also the possession of link that protect the biology from excess light), photosynthesis making use of oxygen may be carefully linked come adaptations to make it through on land.


Section Summary

Prokaryotes (domains Archaea and also Bacteria) room single-celled biology that lack a nucleus. They have actually a single piece of one DNA in the nucleoid area the the cell. Many prokaryotes have a cell wall that lies exterior the border of the plasma membrane. Some prokaryotes may have extr structures such together a capsule, flagella, and pili. Bacteria and also Archaea differ in the lipid composition of their cell membranes and also the qualities of the cell wall. In archaeal membranes, phytanyl units, fairly than fat acids, are connected to glycerol. Some archaeal membranes space lipid monolayers instead of bilayers.

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

Prokaryotes deserve to transfer DNA indigenous one cabinet to an additional by three mechanisms: transformation (uptake of environmental DNA), transduction (transfer the genomic DNA via viruses), and conjugation (transfer the DNA by straight cell contact).


(Figure) i beg your pardon of the adhering to statements is true?

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

The presence of a membrane-enclosed cell core is a characteristic of ________.

prokaryotic cellseukaryotic cellsall cellsviruses

Which of the complying with consist of prokaryotes cells?

bacteria and fungiarchaea and also fungiprotists and animalsbacteria and archaea

The cell wall surface is ________.

interior come the cabinet membraneexterior come the cell membranea component of the cabinet membraneinterior or exterior, relying on the details cell

B


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

fungibacteriavirusesarchaea

B


Prokaryotes stain together Gram-positive or Gram-negative because of distinctions in the cabinet _______.

wallcytoplasmnucleuschromosome

Pseudopeptidoglycan is a characteristics of the wall surfaces of ________.

eukaryotic cellsbacterial prokaryotes cellsarchaean prokaryotic cellsbacterial and archaean prokaryotes cells

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

archaean cellsGram-negative bacteriabacterial prokaryotes cellseukaryotic cells

B


Critical reasoning Questions


Mention 3 differences in between bacteria and archaea.


Responses will vary. A feasible answer is: Bacteria contain peptidoglycan in the cabinet wall; archaea perform not. The cabinet membrane in bacteria is a lipid bilayer; in archaea, it deserve to be a lipid double layer or a monolayer. Bacteria contain fatty acids top top the cabinet membrane, whereas archaea save phytanyl.


Explain the statement the both types, bacteria and archaea, have actually the same basic structures, but built from different chemical components.

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


A scientist isolates a brand-new species that prokaryote. That notes the the specimen is a bacillus v a lipid bilayer and also cell wall that stains optimistic for peptidoglycan. Its one 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? how do friend know?


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


Glossary

capsuleexternal structure that permits a prokaryote to connect to surfaces and protects it from dehydrationconjugationprocess by which prokaryotes relocate DNA from one separation, personal, instance to an additional using a pilusGram negativebacterium who cell wall surface contains small peptidoglycan but has an external membraneGram positivebacterium that consists of mainly peptidoglycan in its cabinet wallspeptidoglycanmaterial composed 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 however contains various sugarsS-layersurface-layer protein current on the external of cell wall surfaces of archaea and also bacteriateichoic acidpolymer associated with the cell wall surface of Gram-positive bacteriatransductionprocess by which a bacteriophage move DNA from one prokaryote come anothertransformationprocess through which a prokaryote takes in DNA uncovered in its environment that is shed by other prokaryotes