Learning Objectives

By the finish of this section, friend will have the ability to do the following:

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

There are plenty of differences in between prokaryotic and eukaryotic cells. The name “prokaryote” argues that prokaryotes are identified by exclusion—they are not eukaryotes, or organisms whose cell contain a nucleus and other internal membrane-bound organelles. However, all cells have four usual structures: the plasma membrane, which features as a obstacle for the cell and also separates the cabinet from that is environment; the cytoplasm, a facility solution of necessary molecules and salts inside the cell; a double-stranded DNA genome, the informational archive of the cell; and ribosomes, whereby protein synthetic takes place. Prokaryotes come in miscellaneous shapes, yet many loss into 3 categories: cocci (spherical), bacilli (rod-shaped), and also spirilli (spiral-shaped) ((Figure)).

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Common prokaryotes cell types. Prokaryotes loss into three an easy categories based on their shape, visualized right here 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: modification of work by zenit Haney Carr, Dr. Richard Facklam, CDC; credit c: change of work-related by Dr. David Cox; scale-bar data native Matt Russell)


Recall that prokaryotes are divided into two various domains, Bacteria and Archaea, which in addition to Eukarya, make up the three domains of life ((Figure)).

The three domains of living organisms. Bacteria and also Archaea are both prokaryotes yet differ enough to be put in different domains. One ancestor of modern-day Archaea is believed to have provided rise come Eukarya, the 3rd domain that life. Major groups that Archaea and Bacteria room shown.


Other bacterial phyla. Chlamydia, Spirochetes, Cyanobacteria, and Gram-positive bacteria are described in this table. Keep in mind that bacterial form is not phylum-dependent; bacteria in ~ a phylum may be cocci, rod-shaped, or spiral. (credit “Chlamydia trachomatis”: alteration of work-related by Dr. Lance Liotta Laboratory, NCI; credit “Treponema pallidum”: modification of work by Dr. David Cox, CDC; credit transaction “Phormidium”: change of occupational by USGS; credit “Clostridium difficile”: modification of occupational by Lois S. Wiggs, CDC; scale-bar data from Matt Russell)

Archaeal phyla. Archaea room separated into 4 phyla: the Korarchaeota, Euryarchaeota, Crenarchaeota, and Nanoarchaeota. (credit “Halobacterium”: alteration of work-related by NASA; credit transaction “Nanoarchaeotum equitans”: alteration of occupational by knife O. Stetter; credit transaction “Korarchaeota”: modification of occupational by Office of science of the U.S. Dept. The Energy; scale-bar data from Matt Russell)
The Plasma Membrane the ProkaryotesThe prokaryotic plasma membrane is a slim lipid bilayer (6 to 8 nanometers) that totally surrounds the cell and separates the within from the outside. That selectively permeable nature keeps ions, proteins, and other molecules in ~ the cell and prevents them indigenous diffusing into the extracellular environment, while other molecules might move with the membrane. Recall that the basic structure that a cell membrane is a phospholipid bilayer created of 2 layers that lipid molecules. In archaeal cell membranes, isoprene (phytanyl) chains attached to glycerol replace the fatty acids connected to glycerol in bacterial membranes. Part archaeal membranes room lipid monolayers rather of bilayers ((Figure)).

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

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

Bacterial cell wall surfaces contain peptidoglycan, created of polysaccharide chains that room cross-linked by unusual peptides include both L- and also D-amino acids including D-glutamic acid and D-alanine. (Proteins normally have just L-amino acids; as a consequence, countless of our antibiotics job-related by mimicking D-amino acids and also therefore have details effects on bacterial cell-wall development.) over there are more than 100 different forms that peptidoglycan. S-layer (surface layer) proteins are also present ~ above the exterior of cell walls of both Archaea and Bacteria.

Bacteria are split into two major groups: Gram positive and also Gram negative, based on their reaction come Gram staining. Note that every Gram-positive bacteria belong come one phylum; bacteria in the various other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. The Gram staining an approach is called after its inventor, Danish scientist Hans Christian Gram (1853–1938). The different bacterial responses come the staining procedure space ultimately because of cell wall surface structure. Gram-positive organisms commonly lack the outer membrane found in Gram-negative organisms ((Figure)). Approximately 90 percent the the cell-wall in Gram-positive bacteria is written of peptidoglycan, and also most the the remainder is written of acidic substances called teichoic acids. Teichoic acids might be covalently attached to lipids in the plasma membrane to kind lipoteichoic acids. Lipoteichoic acids anchor the cell wall surface to the cabinet membrane. Gram-negative bacteria have a reasonably thin cell wall surface composed the a few layers of peptidoglycan (only 10 percent of the complete cell wall), surrounding by an external envelope comprise lipopolysaccharides (LPS) and also lipoproteins. This external envelope is sometimes referred to together a 2nd lipid bilayer. The chemistry that this outer envelope is really different, however, from that of the common lipid bilayer that creates plasma membranes.

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

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

Archaean cabinet walls carry out not have actually peptidoglycan. Over there are four different varieties of archaean cabinet walls. One type is written of pseudopeptidoglycan, which is similar to peptidoglycan in morphology however contains various sugars in the polysaccharide chain. The various other three species of cell walls room composed the polysaccharides, glycoproteins, or pure protein. Other differences between Bacteria and Archaea space seen in (Figure). Keep in mind that features related come DNA replication, transcription and also translation in Archaea are comparable to those viewed in eukaryotes.

Differences and Similarities in between Bacteria and also ArchaeaStructural CharacteristicBacteriaArchaea
Cell typeProkaryoticProkaryotic
Cell morphologyVariableVariable
Cell wallContains peptidoglycanDoes not 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 in prokaryotes is asexual and also usually takes ar by binary fission. (Recall the the DNA that a prokaryote is a single, circular chromosome.) Prokaryotes do not undergo mitosis; instead, the chromosome is replicated and the 2 resulting duplicates separate from one another, as result of the expansion of the cell. The prokaryote, currently enlarged, is pinched inward in ~ its equator and the 2 resulting cells, which room clones, separate. Binary fission go not provide an chance for hereditary recombination or hereditary diversity, but prokaryotes deserve to share genes by three other mechanisms.

In transformation, the prokaryote takes in DNA burned by various other prokaryotes right into its environment. If a nonpathogenic bacterium takes up DNA because that a toxin gene indigenous a microorganism and incorporates the brand-new DNA into its own chromosome, it too may end up being pathogenic. In transduction, bacteriophages, the viruses that infect bacteria, may move brief pieces of chromosomal DNA native one bacter to another. Transduction outcomes in a recombinant organism. Archaea likewise have viruses that may translocate genetic material native one individual to another. In conjugation, DNA is moved from one prokaryote to another by means of a pilus, which bring the biology into call with one another, and provides a channel for carry 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. These three processes of DNA exchange are displayed in (Figure).

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

Gene carry mechanisms in prokaryotes. There space three mechanisms whereby prokaryotes deserve to exchange DNA. In (a) transformation, the cell takes up prokaryotic DNA directly from the environment. The DNA might remain different as plasmid DNA or be included into the hold genome. In (b) transduction, a bacteriophage injects DNA into the cell that consists of a small fragment the DNA indigenous a various prokaryote. In (c) conjugation, DNA is moved from one cabinet to one more via a adjustment bridge, or pilus, that connects the two cells after ~ the sex pilus paint, etc the two bacteria close enough to kind the bridge.
The advancement of ProkaryotesHow perform scientists prize questions about the advancement of prokaryotes? Unlike through animals, artifacts in the fossil record of prokaryotes market very tiny information. Fossils of old prokaryotes look prefer tiny bubbles in rock. Some scientists rotate to genetics and also to the principle of the molecule clock, which holds that the much more recently two species have diverged, the more similar their gene (and hence proteins) will certainly be. Conversely, varieties that sail long earlier will have much more genes that are dissimilar.

Scientists at the NASA Astrobiology Institute and at the europe Molecular Biology activities collaborated to analysis the molecular advancement of 32 certain proteins usual to 72 types of prokaryotes.1 The design they derived from your data shows that three necessary groups the bacteria—Actinobacteria, Deinococcus, and Cyanobacteria (collectively dubbed Terrabacteria through the authors)—were the an initial to colonize land. Actinobacteria are a group of very common Gram-positive bacteria that create branched structures like fungal mycelia, and include varieties important in decomposition of organic wastes. You will recall that Deinococcus is a genus that bacterium that is very resistant to ionization radiation. It has a special peptidoglycan great in enhancement to a 2nd external membrane, so the has features of both Gram-positive and also Gram-negative bacteria.

Cyanobacteria room photosynthesizers, and were more than likely responsible for the production of oxygen ~ above the old earth. The timelines of aberration suggest the bacteria (members that the domain Bacteria) sail from usual ancestral species between 2.5 and 3.2 billion years ago, vice versa, the Archaea diverged earlier: in between 3.1 and 4.1 billion years ago. Eukarya later diverged indigenous the archaean line. The work-related further argues that stromatolites that formed prior come the advent of cyanobacteria (about 2.6 billion years ago) photosynthesized in one anoxic environment and that since of the modifications of the Terrabacteria because that land (resistance to drying and the possession of compounds that defend the organism from overabundance light), photosynthesis making use of oxygen might be carefully linked to adaptations to survive on land.

Section Summary

Prokaryotes (domains Archaea and also Bacteria) are single-celled biology that absence a nucleus. They have a single piece of circular DNA in the newly closed area that the cell. Many prokaryotes have actually a cell wall surface that lies external the boundary of the plasma membrane. Some prokaryotes may have added structures such as a capsule, flagella, and also pili. Bacteria and also Archaea different in the lipid ingredient of their cell membranes and the characteristics of the cabinet wall. In archaeal membranes, phytanyl units, fairly than fat acids, are connected to glycerol. Some archaeal membranes are lipid monolayers rather of bilayers.

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

Prokaryotes can transfer DNA indigenous one cell to one more by three mechanisms: transformation (uptake of ecological DNA), transduction (transfer the genomic DNA via viruses), and conjugation (transfer that DNA by direct cell contact).

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

Gram-positive bacteria have actually a single cell wall surface anchored come the cell membrane by lipoteichoic acid.Porins enable entry the 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 the peptidoglycan, vice versa, Gram-positive bacteria have actually a cell wall made of lipoteichoic acid.

The existence of a membrane-enclosed cell nucleus is a characteristic of ________.

prokaryotic cellseukaryotic cellsall cellsviruses

Which the the adhering to consist of prokaryotes cells?

bacteria and fungiarchaea and also fungiprotists and animalsbacteria and also archaea

The cell wall is ________.

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


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



Prokaryotes stain together Gram-positive or Gram-negative since of differences in the cell _______.


Pseudopeptidoglycan is a properties of the walls of ________.

eukaryotic cellsbacterial prokaryotes cellsarchaean prokaryotes cellsbacterial and also archaean prokaryotic cells

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

archaean cellsGram-negative bacteriabacterial prokaryotic cellseukaryotic cells


Critical reasoning Questions

Mention 3 differences between bacteria and also archaea.

Responses will certainly vary. A feasible answer is: Bacteria save on computer peptidoglycan in the cabinet wall; archaea perform not. The cabinet membrane in bacteria is a lipid bilayer; in archaea, it have the right to be a lipid bilayer or a monolayer. Bacteria contain fat acids ~ above the cell membrane, vice versa, archaea contain phytanyl.

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

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Both bacteria and also archaea have actually cell membranes and also they both contain a hydrophobic portion. In the situation of bacteria, it is a fat acid; in the situation of archaea, it is a hydrocarbon (phytanyl). Both bacteria and archaea have actually a cell wall that protects them. In the instance of bacteria, it is composed of peptidoglycan, whereas 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 new species that prokaryote. The notes the the specimen is a bacillus v a lipid bilayer and also cell wall that stains hopeful for peptidoglycan. Its one chromosome replicates indigenous a single origin the replication. Is the specimen most most likely an Archaea, a Gram-positive bacterium, or a Gram-negative bacterium? just how do friend know?

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


capsuleexternal framework that permits a prokaryote to affix to surfaces and also protects that from dehydrationconjugationprocess whereby prokaryotes move DNA from one individual to another using a pilusGram negativebacterium who cell wall surface contains small peptidoglycan yet has an external membraneGram positivebacterium that contains mainly peptidoglycan in its cabinet wallspeptidoglycanmaterial composed of polysaccharide chain cross-linked to unexplained peptidespilussurface appendage of part prokaryotes supplied for attachments to surfaces consisting of other prokaryotespseudopeptidoglycancomponent that archaea cell wall surfaces that is similar to peptidoglycan in morphology but contains various sugarsS-layersurface-layer protein existing on the outside of cell wall surfaces of archaea and bacteriateichoic acidpolymer associated with the cell wall surface of Gram-positive bacteriatransductionprocess by which a bacteriophage move DNA indigenous one prokaryote come anothertransformationprocess by which a prokaryote takes in DNA found in its atmosphere that is shed by other prokaryotes