Which Of The Following Statements Is True Regarding Bacteria And Animal Cells?
Prokaryotes: Leaner and Archaea
111 Structure of Prokaryotes: Bacteria and Archaea
Learning Objectives
By the cease of this section, yous will be able to exercise the following:
- Depict the basic structure of a typical prokaryote
- Depict of import differences in structure between Archaea and Bacteria
There are many differences between prokaryotic and eukaryotic cells. The name "prokaryote" suggests that prokaryotes are defined by exclusion—they are not eukaryotes, or organisms whose cells contain a nucleus and other internal membrane-bound organelles. However, all cells take 4 common structures: the plasma membrane, which functions as a bulwark for the cell and separates the cell from its environs; the cytoplasm, a complex solution of organic molecules and salts inside the jail cell; a double-stranded Deoxyribonucleic acid genome, the informational archive of the prison cell; and ribosomes, where protein synthesis takes place. Prokaryotes come in various shapes, but many fall into three categories: cocci (spherical), bacilli (rod-shaped), and spirilli (screw-shaped) ((Figure)).
The Prokaryotic Cell
Recall that prokaryotes are unicellular organisms that lack membrane-spring organelles or other internal membrane-bound structures ((Effigy)). Their chromosome—usually single—consists of a piece of round, double-stranded DNA located in an area of the cell called the nucleoid. Most prokaryotes have a prison cell wall outside the plasma membrane. The cell wall functions as a protective layer, and it is responsible for the organism'due south shape. Some bacterial species have a capsule outside the prison cell wall. The capsule enables the organism to attach to surfaces, protects it from dehydration and attack by phagocytic cells, and makes pathogens more resistant to our immune responses. Some species also have flagella (singular, flagellum) used for locomotion, and pili (singular, pilus) used for attachment to surfaces including the surfaces of other cells. Plasmids, which consist of extra-chromosomal DNA, are as well nowadays in many species of bacteria and archaea.
Recollect that prokaryotes are divided into 2 different domains, Bacteria and Archaea, which together with Eukarya, contain the three domains of life ((Figure)).
Characteristics of bacterial phyla are described in (Effigy) and (Effigy). Major bacterial phyla include the Proteobacteria, the Chlamydias, the Spirochaetes, the photosynthetic Cyanobacteria, and the Gram-positive bacteria. The Proteobacteria are in plow subdivided into several classes, from the Alpha- to the Epsilon proteobacteria. Eukaryotic mitochondria are thought to exist the descendants of alphaproteobacteria, while eukaryotic chloroplasts are derived from blue-green alga. Archaeal phyla are described in (Figure).
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. Its selectively permeable nature keeps ions, proteins, and other molecules within the cell and prevents them from diffusing into the extracellular surroundings, while other molecules may motility through the membrane. Call up that the general construction of a cell membrane is a phospholipid bilayer composed of two layers of lipid molecules. In archaeal cell membranes, isoprene (phytanyl) chains linked to glycerol replace the fat acids linked to glycerol in bacterial membranes. Some archaeal membranes are lipid monolayers instead of bilayers ((Effigy)).
The Prison cell Wall of Prokaryotes
The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes. Therefore, the osmotic pressure within the cell is relatively high. The cell wall is a protective layer that surrounds some cells and gives them shape and rigidity. It is located exterior the cell membrane and prevents osmotic lysis (bursting due to increasing volume). The chemic composition of the prison cell wall varies between Archaea and Leaner, and also varies between bacterial species.
Bacterial cell walls contain peptidoglycan, composed of polysaccharide chains that are cross-linked by unusual peptides containing both L- and D-amino acids including D-glutamic acrid and D-alanine. (Proteins normally have only L-amino acids; as a outcome, many of our antibiotics work by mimicking D-amino acids and therefore have specific furnishings on bacterial cell-wall development.) There are more than 100 unlike forms of peptidoglycan. South-layer (surface layer) proteins are also present on the exterior of cell walls of both Archaea and Bacteria.
Bacteria are divided into two major groups: Gram positive and Gram negative , based on their reaction to Gram staining. Notation that all Gram-positive bacteria belong to ane phylum; bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. The Gram staining method is named afterwards its inventor, Danish scientist Hans Christian Gram (1853–1938). The unlike bacterial responses to the staining procedure are ultimately due to cell wall structure. Gram-positive organisms typically lack the outer membrane plant in Gram-negative organisms ((Figure)). Upwards to ninety percent of the cell-wall in Gram-positive bacteria is composed of peptidoglycan, and most of the remainder is composed of acidic substances called teichoic acids. Teichoic acids may exist covalently linked to lipids in the plasma membrane to form lipoteichoic acids. Lipoteichoic acids anchor the cell wall to the jail cell membrane. Gram-negative leaner have a relatively thin cell wall composed of a few layers of peptidoglycan (but ten percent of the full prison cell wall), surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. This outer envelope is sometimes referred to as a second lipid bilayer. The chemical science of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes.
Visual Connectedness
Which of the following statements is true?
- Gram-positive leaner accept a unmarried cell wall anchored to the jail cell membrane past lipoteichoic acid.
- Porins allow entry of substances into both Gram-positive and Gram-negative bacteria.
- The prison cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.
- Gram-negative bacteria accept a cell wall made of peptidoglycan, whereas Gram-positive leaner have a prison cell wall made of lipoteichoic acid.
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Archaean prison cell walls do not take peptidoglycan. There are four dissimilar types of archaean cell walls. One type is composed of pseudopeptidoglycan, which is similar to peptidoglycan in morphology just contains dissimilar sugars in the polysaccharide chain. The other three types of cell walls are composed of polysaccharides, glycoproteins, or pure poly peptide. Other differences between Bacteria and Archaea are seen in (Figure). Note that features related to DNA replication, transcription and translation in Archaea are similar to those seen in eukaryotes.
Differences and Similarities between Leaner and Archaea | ||
---|---|---|
Structural Characteristic | Bacteria | Archaea |
Cell type | Prokaryotic | Prokaryotic |
Cell morphology | Variable | Variable |
Cell wall | Contains peptidoglycan | Does not contain peptidoglycan |
Cell membrane blazon | Lipid bilayer | Lipid bilayer or lipid monolayer |
Plasma membrane lipids | Fatty acids-glycerol ester | Phytanyl-glycerol ethers |
Chromosome | Typically circular | Typically circular |
Replication origins | Single | Multiple |
RNA polymerase | Single | Multiple |
Initiator tRNA | Formyl-methionine | Methionine |
Streptomycin inhibition | Sensitive | Resistant |
Calvin cycle | Yep | No |
Reproduction
Reproduction in prokaryotes is asexual and usually takes identify by binary fission. (Call up that the DNA of a prokaryote is a unmarried, circular chromosome.) Prokaryotes do non undergo mitosis; instead, the chromosome is replicated and the two resulting copies separate from 1 another, due to the growth of the cell. The prokaryote, now enlarged, is pinched inward at its equator and the ii resulting cells, which are clones, split. Binary fission does not provide an opportunity for genetic recombination or genetic diverseness, but prokaryotes tin share genes by iii other mechanisms.
In transformation, the prokaryote takes in Dna shed by other prokaryotes into its environment. If a nonpathogenic bacterium takes up Dna for a toxin gene from a pathogen and incorporates the new Deoxyribonucleic acid into its own chromosome, it too may become pathogenic. In transduction, bacteriophages, the viruses that infect bacteria, may motility short pieces of chromosomal DNA from ane bacterium to another. Transduction results in a recombinant organism. Archaea also have viruses that may translocate genetic material from one individual to another. In conjugation, DNA is transferred from 1 prokaryote to another by means of a pilus, which brings the organisms into contact with one another, and provides a channel for transfer of Deoxyribonucleic acid. The Dna transferred can be in the form of a plasmid or as a composite molecule, containing both plasmid and chromosomal Dna. These three processes of Deoxyribonucleic acid exchange are shown in (Figure).
Reproduction can exist very rapid: a few minutes for some species. This short generation time coupled with mechanisms of genetic recombination and high rates of mutation effect in the rapid development of prokaryotes, assuasive them to reply to environmental changes (such as the introduction of an antibiotic) very quickly.
Evolution Connection
The Evolution of ProkaryotesHow do scientists answer questions about the evolution of prokaryotes? Unlike with animals, artifacts in the fossil record of prokaryotes offer very little information. Fossils of ancient prokaryotes look like tiny bubbles in rock. Some scientists turn to genetics and to the principle of the molecular clock, which holds that the more than recently 2 species accept diverged, the more similar their genes (and thus proteins) will exist. Conversely, species that diverged long ago will have more genes that are dissimilar.
Scientists at the NASA Astrobiology Institute and at the European Molecular Biology Laboratory collaborated to clarify the molecular evolution of 32 specific proteins common to 72 species of prokaryotes. 1 The model they derived from their data indicates that three important groups of bacteria—Actinobacteria, Deinococcus, and Cyanobacteria (collectively called Terrabacteria by the authors)—were the kickoff to colonize land. Actinobacteria are a group of very common Gram-positive bacteria that produce branched structures similar fungal mycelia, and include species of import in decomposition of organic wastes. Yous will call up that Deinococcus is a genus of bacterium that is highly resistant to ionizing radiation. It has a thick peptidoglycan layer in addition to a second external membrane, so information technology has features of both Gram-positive and Gram-negative bacteria.
Blue-green alga are photosynthesizers, and were probably responsible for the product of oxygen on the ancient earth. The timelines of departure advise that bacteria (members of the domain Bacteria) diverged from mutual ancestral species between 2.5 and three.two billion years ago, whereas the Archaea diverged earlier: between 3.1 and four.1 billion years ago. Eukarya later diverged from the archaean line. The work further suggests that stromatolites that formed prior to the appearance of cyanobacteria (virtually 2.6 billion years ago) photosynthesized in an anoxic environs and that because of the modifications of the Terrabacteria for land (resistance to drying and the possession of compounds that protect the organism from excess calorie-free), photosynthesis using oxygen may be closely linked to adaptations to survive on state.
Department Summary
Prokaryotes (domains Archaea and Bacteria) are single-celled organisms that lack a nucleus. They take a single slice of circular Deoxyribonucleic acid in the nucleoid expanse of the cell. Near prokaryotes accept a cell wall that lies outside the boundary of the plasma membrane. Some prokaryotes may take additional structures such as a capsule, flagella, and pili. Bacteria and Archaea differ in the lipid composition of their jail cell membranes and the characteristics of the jail cell wall. In archaeal membranes, phytanyl units, rather than fatty acids, are linked to glycerol. Some archaeal membranes are lipid monolayers instead of bilayers.
The jail cell wall is located exterior the jail cell membrane and prevents osmotic lysis. The chemical composition of cell walls varies betwixt species. Bacterial jail cell walls contain peptidoglycan. Archaean jail cell walls do not take peptidoglycan, but they may have pseudopeptidoglycan, polysaccharides, glycoproteins, or protein-based cell walls. Bacteria tin can be divided into two major groups: Gram positive and Gram negative, based on the Gram stain reaction. Gram-positive organisms have a thick peptidoglycan layer fortified with teichoic acids. Gram-negative organisms have a thin cell wall and an outer envelope containing lipopolysaccharides and lipoproteins.
Prokaryotes can transfer Dna from one cell to another by iii mechanisms: transformation (uptake of environmental DNA), transduction (transfer of genomic Dna via viruses), and conjugation (transfer of Dna past direct prison cell contact).
Visual Connectedness Questions
(Figure) Which of the following statements is true?
- Gram-positive bacteria have a single cell wall anchored to the jail cell membrane by lipoteichoic acrid.
- Porins allow entry of substances into both Gram-positive and Gram-negative bacteria.
- The prison cell wall of Gram-negative bacteria is thick, and the prison cell wall of Gram-positive bacteria is thin.
- Gram-negative bacteria take a cell wall made of peptidoglycan, whereas Gram-positive bacteria take a cell wall made of lipoteichoic acrid.
(Figure) A
Review Questions
The presence of a membrane-enclosed nucleus is a characteristic of ________.
- prokaryotic cells
- eukaryotic cells
- all cells
- viruses
B
Which of the following consist of prokaryotic cells?
- bacteria and fungi
- archaea and fungi
- protists and animals
- bacteria and archaea
D
The jail cell wall is ________.
- interior to the prison cell membrane
- exterior to the cell membrane
- a office of the prison cell membrane
- interior or exterior, depending on the particular cell
B
Organisms near likely to be plant in extreme environments are ________.
- fungi
- bacteria
- viruses
- archaea
B
Prokaryotes stain as Gram-positive or Gram-negative because of differences in the cell _______.
- wall
- cytoplasm
- nucleus
- chromosome
A
Pseudopeptidoglycan is a characteristic of the walls of ________.
- eukaryotic cells
- bacterial prokaryotic cells
- archaean prokaryotic cells
- bacterial and archaean prokaryotic cells
C
The lipopolysaccharide layer (LPS) is a characteristic of the wall of ________.
- archaean cells
- Gram-negative bacteria
- bacterial prokaryotic cells
- eukaryotic cells
B
Critical Thinking Questions
Mention 3 differences between leaner and archaea.
Responses volition vary. A possible answer is: Leaner contain peptidoglycan in the cell wall; archaea exercise not. The cell membrane in leaner is a lipid bilayer; in archaea, information technology can exist a lipid bilayer or a monolayer. Bacteria contain fat acids on the cell membrane, whereas archaea incorporate phytanyl.
Explain the argument that both types, bacteria and archaea, have the aforementioned basic structures, but built from different chemic components.
Both leaner and archaea take jail cell membranes and they both contain a hydrophobic portion. In the example of bacteria, it is a fatty acid; in the example of archaea, it is a hydrocarbon (phytanyl). Both bacteria and archaea accept a cell wall that protects them. In the case of bacteria, information technology is composed of peptidoglycan, whereas in the case of archaea, it is pseudopeptidoglycan, polysaccharides, glycoproteins, or pure protein. Bacterial and archaeal flagella too differ in their chemical construction.
A scientist isolates a new species of prokaryote. He notes that the specimen is a bacillus with a lipid bilayer and jail cell wall that stains positive for peptidoglycan. Its round chromosome replicates from a single origin of replication. Is the specimen most probable an Archaea, a Gram-positive bacterium, or a Gram-negative bacterium? How do you know?
The specimen is nearly 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.
Footnotes
- 1 Battistuzzi, FU, Feijao, A, and Hedges, SB. A genomic timescale of prokaryote evolution: Insights into the origin of methanogenesis, phototrophy, and the colonization of land. BioMed Central: Evolutionary Biology 4 (2004): 44, doi:10.1186/1471-2148-4-44.
Glossary
- capsule
- external structure that enables a prokaryote to attach to surfaces and protects it from dehydration
- conjugation
- process by which prokaryotes move Dna from ane private to another using a hair
- Gram negative
- bacterium whose cell wall contains petty peptidoglycan but has an outer membrane
- Gram positive
- bacterium that contains mainly peptidoglycan in its prison cell walls
- peptidoglycan
- material composed of polysaccharide chains cantankerous-linked to unusual peptides
- pilus
- surface appendage of some prokaryotes used for zipper to surfaces including other prokaryotes
- pseudopeptidoglycan
- component of archaea cell walls that is similar to peptidoglycan in morphology only contains unlike sugars
- S-layer
- surface-layer protein present on the outside of cell walls of archaea and bacteria
- teichoic acid
- polymer associated with the cell wall of Gram-positive bacteria
- transduction
- process past which a bacteriophage moves Deoxyribonucleic acid from one prokaryote to another
- transformation
- process past which a prokaryote takes in Dna found in its environment that is shed by other prokaryotes
Source: https://opentextbc.ca/biology2eopenstax/chapter/structure-of-prokaryotes-bacteria-and-archaea/
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