Figure Which of the following statements is true? Responses will vary. A possible answer is: Bacteria contain peptidoglycan in the cell wall; archaea do not.
The cell membrane in bacteria is a lipid bilayer; in archaea, it can be a lipid bilayer or a monolayer. Bacteria contain fatty acids on the cell membrane, whereas archaea contain phytanyl.
Explain the statement that both types, bacteria and archaea, have the same basic structures, but built from different chemical components. Both bacteria and archaea have cell membranes and they both contain a hydrophobic portion. In the case of bacteria, it is a fatty acid; in the case of archaea, it is a hydrocarbon phytanyl. Both bacteria and archaea have a cell wall that protects them. In the case of bacteria, it is composed of peptidoglycan, whereas in the case of archaea, it is pseudopeptidoglycan, polysaccharides, glycoproteins, or pure protein.
Bacterial and archaeal flagella also differ in their chemical structure. A scientist isolates a new species of prokaryote. He notes that the specimen is a bacillus with a lipid bilayer and cell wall that stains positive for peptidoglycan. Its circular chromosome replicates from a single origin of replication. Is the specimen most likely an Archaea, a Gram-positive bacterium, or a Gram-negative bacterium? How do you know? The specimen is most likely a gram-positive bacterium.
Since the cell wall contains peptidoglycan and the chromosome has one origin of replication, we can conclude that the specimen is in the Domain Bacteria. Since the gram stain detects peptidoglycan, the prokaryote is a gram-positive bacterium. Skip to content Prokaryotes: Bacteria and Archaea.
Learning Objectives By the end of this section, you will be able to do the following: Describe the basic structure of a typical prokaryote Describe important differences in structure between Archaea and Bacteria. Common prokaryotic cell types. Prokaryotes fall into three basic categories based on 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.
David Cox; scale-bar data from Matt Russell. The Prokaryotic Cell Recall that prokaryotes are unicellular organisms that lack membrane-bound organelles or other internal membrane-bound structures Figure. The features of a typical prokaryotic cell.
Flagella, capsules, and pili are not found in all prokaryotes. The three domains of living organisms. Bacteria and Archaea are both prokaryotes but differ enough 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 of Archaea and Bacteria are shown. The Proteobacteria.
Phylum Proteobacteria is one of up to 52 bacteria phyla. Proteobacteria is further subdivided into five classes, Alpha through Epsilon. Archaeal phyla. The Plasma Membrane of Prokaryotes The prokaryotic plasma membrane is a thin lipid bilayer 6 to 8 nanometers that completely surrounds the cell and separates the inside from the outside.
Bacterial and archaeal phospholipids. Archaeal phospholipids differ from those found in Bacteria and Eukarya in two ways. First, they have branched phytanyl sidechains instead of linear ones. Second, an ether bond instead of an ester bond connects the lipid to the glycerol. The Cell Wall of Prokaryotes The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes. Visual Connection. Cell walls in Gram-positive and Gram-negative bacteria. Bacteria are divided into two major groups: Gram positive and Gram negative.
Both groups have a cell wall composed of peptidoglycan: in Gram-positive bacteria, the wall is thick, whereas in Gram-negative bacteria, the wall is thin. In Gram-negative bacteria, the cell wall is surrounded by an outer membrane that contains lipopolysaccharides and lipoproteins.
Porins are proteins in this cell membrane that allow substances to pass through the outer membrane of Gram-negative bacteria. In Gram-positive bacteria, lipoteichoic acid anchors the cell wall to the cell membrane.
Reproduction Reproduction in prokaryotes is asexual and usually takes place by binary fission. Gene transfer mechanisms in prokaryotes. There are three mechanisms by which prokaryotes can exchange DNA. In a transformation, the cell takes up prokaryotic DNA directly from the environment.
In b transduction, a bacteriophage injects DNA into the cell that contains a small fragment of DNA from a different prokaryote. In c conjugation, DNA is transferred from one cell to another via a mating bridge, or pilus, that connects the two cells after the sex pilus draws the two bacteria close enough to form the bridge.
The fossil record indicates that the first living organisms were prokaryotes Bacteria and Archaea , and eukaryotes arose a billion years later. Study Tip: It is suggested that you create a chart to compare and contrast the three domains of life as you read.
The information below was adapted from OpenStax Biology Prokaryotes have been and are able to live in every environment by using whatever energy and carbon sources are available. Prokaryotes fill many niches on Earth, including being involved in nutrient cycles such as nitrogen and carbon cycles, decomposing dead organisms, and thriving inside living organisms, including humans.
The very broad range of environments that prokaryotes occupy is possible because they have diverse metabolic processes. Phototrophs or phototrophic organisms obtain their energy from sunlight. Chemotrophs or chemosynthetic organisms obtain their energy from chemical compounds. Prokaryotes not only can use different sources of energy but also different sources of carbon compounds. Recall that organisms that are able to fix inorganic carbon for example, carbon dioxide into organic carbon for example, glucose are called autotrophs.
In contrast, heterotrophs must obtain carbon from organic compounds. The terms that describe how prokaryotes obtain energy and carbon can be combined. Thus, photoautotrophs use energy from sunlight, and carbon from carbon dioxide and water, whereas chemoheterotrophs obtain energy and carbon from an organic chemical source. Chemoautotrophs obtain their energy from inorganic compounds, and they build their complex molecules from carbon dioxide. Finally, photoheterotrophs use light as an energy source, but require an organic carbon source they cannot fix carbon dioxide into organic carbon.
In contrast to the great metabolic diversity of prokaryotes, eukaryotes are only photoautotrophs plants and some protists or chemoheterotrophs animals, fungi, and some protists. The table below summarizes carbon and energy sources in prokaryotes.
The videos below provide more detailed overviews of Archaea and Bacteria, including general features and metabolic diversity:. Archaea: cell membrane contains ether linkages; cell wall lacks peptidoglycan; genes and enzymes behave more like Eukaryotes; have three RNA polymerases like eukaryotes; and extremophiles. Bacteria: cell membrane contains ester bonds; cell wall made of peptidoglycan; have only one RNA polymerase; react to antibiotics in a different way than archea do. Cite APA 7 lance, r.
Difference Between Archaea and Bacteria. Difference Between Similar Terms and Objects. MLA 8 lance, raa. Archaea only have one RNA polymerase. It is similar to the three found in eucarya which is why it is suspected to be a homolog.
Archaea are no longer considered extemophiles as they are much more ubiquitous than previously thought. I would not consider that a difference; however, the remaining description seems accurate. Granted these significant biochemical differences but do these differences justify breaking bacteria and archaea into two separate domains more-or-less coequal with the very different eukaryotes?
To my knowledge, we have discovered no organisms intermediate between eukaryotes and prokaryotes. However, if such organisms exist it might make more sense placing the bacteria and archaea under a single domain—Bacteria [on top] subdivided into Eubacteria and Archaea.
By the way, using antibiotic pathways to distinguish archaea and bacteria seems to me to be spurious.
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