Learning Objectives

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

Describe the straightforward structure the a typical prokaryoteDescribe important differences in structure in between Archaea and also Bacteria

There are numerous differences in between prokaryotic and also eukaryotic cells. The name “prokaryote” says that prokaryotes are defined by exclusion—they are not eukaryotes, or biology whose cells contain a nucleus and other interior membrane-bound organelles. However, every cells have actually four typical structures: the plasma membrane, which functions as a obstacle for the cell and separates the cabinet from that is environment; the cytoplasm, a complicated solution of essential molecules and also salts within the cell; a double-stranded DNA genome, the informational save on computer of the cell; and also ribosomes, whereby protein synthetic takes place. Prokaryotes come in various shapes, yet many fall into three categories: cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped) ((Figure)).

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Common prokaryotes cell types. Prokaryotes fall into three basic categories based upon their shape, visualized 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 occupational by zenith Haney Carr, Dr. Richard Facklam, CDC; credit transaction c: alteration of work-related by Dr. David Cox; scale-bar data from Matt Russell)


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

The three domain names of life organisms. Bacteria and also Archaea room both prokaryotes but differ sufficient to be placed in separate domains. An ancestor of modern Archaea is believed to have given rise to Eukarya, the third domain of life. Major groups that Archaea and also Bacteria room shown.


Other bacter phyla. Chlamydia, Spirochetes, Cyanobacteria, and Gram-positive bacteria are described in this table. Keep in mind that bacterial form is no phylum-dependent; bacteria in ~ a phylum might be cocci, rod-shaped, or spiral. (credit “Chlamydia trachomatis”: alteration of work by Dr. Lance Liotta Laboratory, NCI; credit “Treponema pallidum”: alteration of work-related by Dr. David Cox, CDC; credit “Phormidium”: alteration of job-related by USGS; credit “Clostridium difficile”: modification of occupational by Lois S. Wiggs, CDC; scale-bar data native Matt Russell)

Archaeal phyla. Archaea space separated into four phyla: the Korarchaeota, Euryarchaeota, Crenarchaeota, and also Nanoarchaeota. (credit “Halobacterium”: alteration of work-related by NASA; credit transaction “Nanoarchaeotum equitans”: modification of job-related by karl O. Stetter; credit transaction “Korarchaeota”: change of occupational by Office of science of the U.S. Dept. The Energy; scale-bar data from Matt Russell)
The Plasma Membrane of ProkaryotesThe prokaryotes plasma membrane is a slim lipid double layer (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 native diffusing right into the extracellular environment, while various other molecules may move through the membrane. Recall that the basic structure the a cell membrane is a phospholipid bilayer created of two layers the lipid molecules. In archaeal cabinet membranes, isoprene (phytanyl) chains connected to glycerol replace the fat acids attached to glycerol in bacterial membranes. Part archaeal membranes room lipid monolayers rather of bilayers ((Figure)).

Bacterial and also archaeal phospholipids. Archaeal phospholipids different from those uncovered in Bacteria and also Eukarya in 2 ways. First, they have branched phytanyl sidechains rather of linear ones. Second, an ether bond instead of an ester link connects the lipid to the glycerol.
The Cell wall of Prokaryotes

The cytoplasm of prokaryotes cells has actually a high concentration of liquified solutes. Therefore, the osmotic pressure within the cabinet is reasonably high. The cell wall surface is a security layer the surrounds some cells and gives castle shape and rigidity. It is located exterior the cell membrane and also prevents osmotic lysis (bursting as result of increasing volume). The chemistry composition that the cell wall varies in between Archaea and also Bacteria, and additionally varies in between bacterial species.

Bacterial cell walls contain peptidoglycan, created of polysaccharide chains that space cross-linked by unusual peptides comprise both L- and D-amino acids including D-glutamic acid and also D-alanine. (Proteins usually have just L-amino acids; together a consequence, many of our antibiotics job-related by mimicking D-amino acids and also therefore have details effects on bacterial cell-wall development.) over there are much more than 100 various forms of peptidoglycan. S-layer (surface layer) proteins are additionally present on the outside of cell walls of both Archaea and also Bacteria.

Bacteria are split into two significant groups: Gram positive and Gram negative, based upon their reaction to Gram staining. Keep in mind that all Gram-positive bacteria belong come one phylum; bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and also others) are Gram-negative. The Gram staining an approach is called after that inventor, Danish scientist Hans Christian Gram (1853–1938). The various bacterial responses to the staining procedure room ultimately as result of cell wall surface structure. Gram-positive organisms commonly lack the external membrane uncovered in Gram-negative organisms ((Figure)). As much as 90 percent of the cell-wall in Gram-positive bacteria is composed of peptidoglycan, and also most the the rest is written of acidic substances called teichoic acids. Teichoic acids may be covalently linked to lipids in the plasma membrane to form lipoteichoic acids. Lipoteichoic acids anchor the cell wall surface to the cabinet membrane. Gram-negative bacteria have actually a relatively thin cell wall surface composed of a few layers of peptidoglycan (only 10 percent the the total cell wall), surrounded by an outer envelope comprise lipopolysaccharides (LPS) and lipoproteins. This outer envelope is occasionally referred to as a second lipid bilayer. The chemistry that this outer envelope is very different, however, from that of the common lipid double layer that develops plasma membranes.

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

Gram-positive bacteria have actually a single cell wall anchored come the cabinet membrane through lipoteichoic acid.Porins allow entry of substances right 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 actually a cell wall made of peptidoglycan, whereas Gram-positive bacteria have a cell wall surface made of lipoteichoic acid.

Archaean cell walls execute not have peptidoglycan. There are 4 different types of archaean cell walls. One type is written of pseudopeptidoglycan, i m sorry is comparable to peptidoglycan in morphology yet contains various sugars in the polysaccharide chain. The various other three varieties of cabinet walls are composed of polysaccharides, glycoproteins, or pure protein. Other differences between Bacteria and also Archaea room seen in (Figure). Keep in mind that attributes related to DNA replication, transcription and translation in Archaea are similar 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 in prokaryotes is asexual and also usually takes ar by binary fission. (Recall the the DNA the a prokaryote is a single, one chromosome.) Prokaryotes carry out not experience mitosis; instead, the chromosome is replicated and the 2 resulting copies separate native one another, as result of the expansion of the cell. The prokaryote, currently enlarged, is pinched inward in ~ its equator and also the two resulting cells, which room clones, separate. Binary fission go not carry out an chance for hereditary recombination or genetic diversity, however prokaryotes have the right to share gene by three various other mechanisms.

In transformation, the prokaryote absorbs DNA melted by various other prokaryotes right into its environment. If a nonpathogenic bacter takes increase DNA because that a toxin gene native a pathogen and incorporates the new DNA into its own chromosome, it also may end up being pathogenic. In transduction, bacteriophages, the viruses that infect bacteria, may move quick pieces the chromosomal DNA native one bacter to another. Transduction outcomes in a recombinant organism. Archaea likewise have viruses that might translocate hereditary material indigenous one separation, personal, instance to another. In conjugation, DNA is moved from one prokaryote to an additional by means of a pilus, which bring the biology into call with one another, and also provides a channel for move of DNA. The DNA transferred deserve to be in the kind of a plasmid or as a composite molecule, comprise both plasmid and chromosomal DNA. This three processes of DNA exchange are presented in (Figure).

Reproduction deserve to be an extremely rapid: a few minutes for some species. This quick generation time coupled v mechanisms of hereditary recombination and also high rates of mutation result in the rapid evolution of prokaryotes, allowing them to respond come environmental changes (such together the arrival of one antibiotic) very quickly.

Gene move mechanisms in prokaryotes. There space three mechanisms whereby prokaryotes have the right to exchange DNA. In (a) transformation, the cabinet takes up prokaryotes DNA straight from the environment. The DNA might remain different as plasmid DNA or be integrated into the organize genome. In (b) transduction, a bacteriophage injects DNA right into the cell that consists of a little fragment that DNA indigenous a various prokaryote. In (c) conjugation, DNA is moved from one cabinet to an additional via a adjustment bridge, or pilus, that connects the two cells ~ the sex pilus draws the two bacteria close enough to type the bridge.
The evolution of ProkaryotesHow carry out scientists price questions about the advancement of prokaryotes? Unlike with animals, artefacts in the fossil record of prokaryotes offer very tiny information. Fossils of ancient prokaryotes look choose tiny bubbles in rock. Part scientists revolve to genetics and also to the principle of the molecular clock, i m sorry holds the the more recently two varieties have diverged, the much more similar their genes (and therefore proteins) will certainly be. Conversely, types that sail long back will have an ext genes that room dissimilar.

Scientists in ~ the NASA Astrobiology Institute and at the european Molecular Biology activities collaborated to analyze the molecular evolution of 32 certain proteins common to 72 varieties of prokaryotes.1 The design they acquired from your data indicates that three essential groups the bacteria—Actinobacteria, Deinococcus, and Cyanobacteria (collectively called Terrabacteria through the authors)—were the very first to colonize land. Actinobacteria room a group of really common Gram-positive bacteria that produce branched structures favor fungal mycelia, and include types important in decomposition of organic wastes. You will certainly recall the Deinococcus is a genus of bacterium that is very resistant to ionizing radiation. It has a thick peptidoglycan great in addition to a second external membrane, so that has functions of both Gram-positive and Gram-negative bacteria.

Cyanobacteria space photosynthesizers, and also were more than likely responsible for the production of oxygen top top the old earth. The timelines of aberration suggest that bacteria (members that the domain Bacteria) sail from typical ancestral species between 2.5 and also 3.2 billion year ago, vice versa, the Archaea sail earlier: in between 3.1 and 4.1 billion years ago. Eukarya later on diverged indigenous the archaean line. The work further suggests that stromatolites that formed prior to the arrival of cyanobacteria (about 2.6 billion years ago) photosynthesized in an anoxic environment and that due to the fact that of the modifications of the Terrabacteria for land (resistance to drying and also the possession of compound that safeguard the biology from overabundance light), photosynthesis making use of oxygen might be closely linked to adaptations to endure on land.

Section Summary

Prokaryotes (domains Archaea and Bacteria) space single-celled biology that lack a nucleus. They have a single piece of one DNA in the newly closed area the the cell. Most prokaryotes have a cell wall surface that lies external the border of the plasma membrane. Some prokaryotes might have additional structures such together a capsule, flagella, and pili. Bacteria and Archaea different in the lipid composition of your cell membranes and the characteristics of the cabinet wall. In archaeal membranes, phytanyl units, quite than fatty acids, are connected to glycerol. Part archaeal membranes room lipid monolayers rather of bilayers.

The cell wall surface is located outside the cell membrane and prevents osmotic lysis. The chemistry composition the cell wall surfaces varies in between species. Bacter cell walls contain peptidoglycan. Archaean cabinet walls do not have peptidoglycan, however they may have actually pseudopeptidoglycan, polysaccharides, glycoproteins, or protein-based cell walls. Bacteria can 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 fortified with teichoic acids. Gram-negative organisms have actually a slim cell wall surface and an external envelope containing lipopolysaccharides and lipoproteins.

Prokaryotes can transfer DNA from one cabinet to another by three mechanisms: revolution (uptake of eco-friendly DNA), transduction (transfer of genomic DNA via viruses), and conjugation (transfer of DNA by straight cell contact).

(Figure) which of the following statements is true?

Gram-positive bacteria have a single cell wall surface anchored to the cell membrane by lipoteichoic acid.Porins allow 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 surface of Gram-positive bacteria is thin.Gram-negative bacteria have actually a cell wall surface made that peptidoglycan, vice versa, Gram-positive bacteria have actually a cell wall made the lipoteichoic acid.

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

prokaryotic cellseukaryotic cellsall cellsviruses

Which that 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, depending upon the specific cell


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



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


Pseudopeptidoglycan is a properties of the walls of ________.

eukaryotic cellsbacterial prokaryotes cellsarchaean prokaryotes cellsbacterial and archaean prokaryotes cells

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

archaean cellsGram-negative bacteriabacterial prokaryotic cellseukaryotic cells


Critical thinking Questions

Mention three differences between bacteria and also archaea.

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

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

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Both bacteria and also archaea have cell membranes and also they both contain a hydrophobic portion. In the situation of bacteria, the is a fatty acid; in the case of archaea, it is a hydrocarbon (phytanyl). Both bacteria and archaea have actually a cell wall that protects them. In the situation of bacteria, that is written of peptidoglycan, vice versa, in the case 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 v a lipid bilayer and cell wall surface that stains optimistic for peptidoglycan. Its one chromosome replicates native a single origin the replication. Is the specimen most most likely an Archaea, a Gram-positive bacterium, or a Gram-negative bacterium? how do girlfriend know?

The specimen is most most likely a gram-positive bacterium. Since 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.


capsuleexternal structure that enables a prokaryote to affix to surfaces and protects the from dehydrationconjugationprocess whereby prokaryotes move DNA indigenous one individual to another using a pilusGram negativebacterium who cell wall surface contains tiny peptidoglycan but has an outer membraneGram positivebacterium that has mainly peptidoglycan in its cell wallspeptidoglycanmaterial written of polysaccharide chain cross-linked to unusual peptidespilussurface appendage of some prokaryotes provided for attachment to surfaces including other prokaryotespseudopeptidoglycancomponent of archaea cell walls that is similar to peptidoglycan in morphology but contains different sugarsS-layersurface-layer protein present on the exterior of cell walls of archaea and also bacteriateichoic acidpolymer connected with the cell wall of Gram-positive bacteriatransductionprocess by which a bacteriophage moves DNA indigenous one prokaryote come anothertransformationprocess by which a prokaryote takes in DNA discovered in its environment that is melted by various other prokaryotes