{"id":135,"date":"2017-09-04T05:03:33","date_gmt":"2017-09-04T05:03:33","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/general-science\/?page_id=135"},"modified":"2017-09-22T13:20:45","modified_gmt":"2017-09-22T13:20:45","slug":"prokaryotes","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/general-science\/prokaryotes\/","title":{"rendered":"Prokaryotes"},"content":{"rendered":"<div class=\"twelve columns\" style=\"margin-top: 10%;\">\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/discovering-cells\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/biochemistry-cell-biology\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/cells-pieces-and-parts\">Next Lesson \u27a1<\/a><\/div>\n<p><!-- CONTENT BEGINS HERE --><\/p>\n<h1 id=\"title\">Prokaryotes<\/h1>\n<h4>Objective<\/h4>\n<p>In this lesson, we will review prokaryotes.<\/p>\n<section>\n<h3>Early Earthlings<\/h3>\n<p>The first organisms to live on Earth were probably primitive prokaryotes\u2014the earliest form of simple, single-celled organisms. <strong>Archaea<\/strong> are the oldest known living things and are grouped in their own domain. Although there is still debate about what organisms actually evolved first, many scientists agree that today\u2019s prokaryotes are their closest relatives. Among these ancient organisms were <strong>methanogens<\/strong>, which synthesize methane from carbon dioxide and hydrogen gases (abundant substances in Earth\u2019s early days);\u00a0<strong>thermoacidophiles<\/strong>, specialized to survive in extremely hot and acidic environment; and <strong>halobacteria<\/strong>, which thrive in highly saline conditions. Many of the archaea still living today are extremophiles, living in and adapted to extreme environmental conditions such as deep-sea vents, hot springs, and geysers.<\/p>\n<p><center><img decoding=\"async\" src=\"http:\/\/americanboard.org\/Subjects\/Images\/gensci\/img\/prokaryote.jpg\" alt=\"Prokayrote\" \/><\/center><\/p>\n<p class=\"figcaption\">Prokaryotic organisms are some of the simplest forms of life on Earth<\/p>\n<h3>No Nukes<\/h3>\n<p>The Archaea probably gave rise to other single-celled prokaryotes called Bacteria (or possibly vice-versa). No matter which organisms came first, we do know that the two most primitive of the three domains of life, are prokaryotic. Their most singular characteristic is their lack of a membrane-bound nucleus and membrane-bound organelles. In prokaryotes, the single, continuous strand of DNA (naked DNA) floats freely in the cytoplasm. Both the Archaea and the Bacteria are prokaryotes.<\/p>\n<p>The fundamental characteristics shared by nearly all prokaryotes include:<\/p>\n<ul>\n<li>a <abbr title=\"among the large class of lipids that contain phosphorus and play important structural or metabolic roles for living cells.\">phospholipid<\/abbr> and cholesterol cell membrane<\/li>\n<li>a complex, polymer (peptidoglycan) cell wall that gives the cell shape, but that may also be rigid or flexible<\/li>\n<li><strong>flagella<\/strong> (singular <em>flagellum<\/em>) or <strong>cilia<\/strong> attached to the cell wall are often present; cilia and flagella beat rapidly to aid locomotion<\/li>\n<li>reproduction is <strong>asexual<\/strong> and commonly by <abbr title=\"an asexual reproduction method that involves the parent cell splitting into two equal parts.\">binary fission<\/abbr>.<\/li>\n<\/ul>\n<h3>Early Earthlings<\/h3>\n<p>Most prokaryote locomotion is accomplished by the rapid beating of the cilia that often completely surround the cell. Some prokaryotes can also have one or more flagella.<\/p>\n<p>Reproduction is usually by binary fission, or cell division. The complex series of steps in mitosis (done in eukaryotes) are not needed among prokaryotes because of their simplified, single-stranded DNA. However, mis-matching and other chemical errors frequently lead to <strong>mutations<\/strong> during the binary split. For many prokaryotes, particularly infectious bacteria, a new generation may arise every 15 minutes. Combine the short generation time with the occurrence of mutations and you can see why bacteria evolve quickly and are able to develop resistance to antibiotics.<\/p>\n<p>Some prokaryotes reproduce via <strong>budding<\/strong>, in which a genetically identical offspring develops out of the parent\u2019s body and eventually buds off from the parent. Some prokaryotes are able to generate <strong>spores<\/strong> that remain dormant, but viable, for long periods. The spores of the bacterium <em>Clostridium botulinum<\/em>, which causes botulism, can survive hours of boiling and still kill you.<\/p>\n<p>Generally, prokaryotes have one of four characteristic shapes:<\/p>\n<ul>\n<li><strong>rod-shaped bacteria<\/strong>, also called <em>bacilli<\/em>, are the gram-positive, aerobic bacteria (e.g., <em>E. coli<\/em>, <em>Listeria<\/em>). Diseases often caused by Bacilli include tuberculosis, whooping cough, and diphtheria.<\/li>\n<li><strong>spherical bacteria<\/strong>, also called <em>cocci<\/em> (e.g., <em>Diplococcus pneumoniae<\/em>). Diseases that are caused by cocci bacteria are staphylococcus infections, food poisoning, urinary tract infections, throat infections, and most pneumonia.<\/li>\n<li><strong>spiral-shaped bacteria<\/strong>, also called <em>spirilla<\/em> (e.g., <em>Spirullum<\/em>). These are rod-like, spiral-shaped bacteria that cause many diseases of infants and fetal infections prior to birth.<\/li>\n<li><strong>incomplete spirals<\/strong> or comma-shaped bacteria called <em>vibrios<\/em> (e.g., <em>Vibrio<\/em>). These are a diverse assemblage of organisms that create bioluminescence in the ocean and cause cholera.<\/li>\n<\/ul>\n<p>Two bacteria that have a unique shape are the <em>spirochetes<\/em> (e.g.,<em>Terponema pallidum<\/em>, which causes syphilis), which can be incredibly long, and <em>rickettsiae<\/em> (e.g.\u00a0<em>Rickettsia prowazeki<\/em>, which causes typhus), which are the smallest cells known.<\/p>\n<h3>Early Eaters<\/h3>\n<p>Most prokaryotes are <strong>heterotrophs<\/strong> that mainly consume dead organic matter. It is to bacteria that we owe the existence of organically rich topsoil, because bacteria decompose organic matter in soil. Some heterotrophic bacteria live <abbr title=\"an interaction between two organisms living together some type of association.\">symbiotically<\/abbr> in hosts, either as <abbr title=\"a symbiotic relationship where one member of the association benefits while the other is not affected (+\/0)\">commensals<\/abbr>, <abbr title=\"a symbiotic relationship where the association is negative and costly to one of the organisms while beneficial to the other (+\/-)\">parasites<\/abbr> (some pathogenic), or in <abbr title=\"symbiotic relationship where the association is beneficial to both organisms (+\/+)\">mutualism<\/abbr> that benefits both organisms. There are even heterotrophic bacteria that are parasites of other bacteria. Some prokaryotes are <strong>chemotrophs<\/strong> that can use inorganic materials as a source of energy. Archaea are largely chemotrophs, particularly the methanogens that still thrive in anaerobic environments. One group of chemotrophs, vital to the nitrogen cycle, transforms inorganic nitrogen and makes it available to plants.<\/p>\n<p>Some bacteria are photosynthetic. In one group of sulfur bacteria, energy derived from the electrons in sulfur atoms take the place of the electrons derived from water in plants. Nonsulfur photosynthetic bacteria are the ancient cyanobacteria, which were extremely important in the formation of the earliest ecosystems. Cyanobacteria are sometimes called blue-green algae, but they are not related to the true algae (which are eukaryotes). Cyanobacteria contain<strong> chlorophyll a<\/strong> and break down water during photosynthesis (as do plants). In the process they release oxygen. The countless cyanophytes that lived in the Earth\u2019s early oceans contributed the oxygen to our atmosphere that we, and most organisms, require to survive. It is probable that cyanophytes gave rise to the first eukaryotic algae.<\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Which of the following is a characteristic of Archaea?<\/p>\n<ol>\n<li>They have at least one flagellum.<\/li>\n<li>They can thrive in extreme environments like high salinity.<\/li>\n<li>They contain no DNA.<\/li>\n<li>They all synthesize hydrocarbons.<\/li>\n<\/ol>\n<p><a class=\"q-answer button button-primary\">Reveal Answer<\/a><\/p>\n<p class=\"q-reveal\">The correct answer is B. The presence or absence of flagella is not a characteristic of Archaea. One type of archaebacteria, the halobacteria, thrive in saline conditions, but only methanogens synthesize hydrocarbons (methane).<\/p>\n<\/section>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>The most common form of reproduction among prokaryotes is<\/p>\n<ol>\n<li>fragmentation.<\/li>\n<li>binary fission.<\/li>\n<li>budding.<\/li>\n<li>sporulation.<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is B. Most prokaryotes reproduce asexually via cell division, or binary fission. Fragmentation is the regeneration of a lost part of the organism, as in starfish. Some prokaryotes do reproduce via budding, but it is not common. Similarly, some prokaryotes produce spores, but this is rare among prokaryotes.<\/p>\n<\/section>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Most prokaryotes are heterotrophs that ingest<\/p>\n<ol>\n<li>autotrophs.<\/li>\n<li>other heterotrophic bacteria.<\/li>\n<li>inorganic matter.<\/li>\n<li>decaying organic matter.<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is D. Most prokaryotes live in soil where they ingest and decompose decaying organic matter and release it back into the soil. Some heterotrophic prokaryotes may consume unicellular autotrophs, but this is not widespread, so A is incorrect. Similarly, some heterotrophic prokaryotes may ingest others of their kind, but this is not common, so B is incorrect. Chemotrophs do metabolize inorganic substances, but they are a small sector of the prokaryotic community, so C is not correct.<\/p>\n<\/section>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>Which of the following bacteria are photosynthetic?<\/p>\n<ol>\n<li>Algae<\/li>\n<li>Vibrios<\/li>\n<li>Mycoplasmas<\/li>\n<li>Cyanobacteria<\/li>\n<\/ol>\n<p><a class=\"button button-primary q-answer\"> Reveal Answer <\/a><\/p>\n<p class=\"q-reveal\">The correct answer is D. Cyanobacteria are photosynthetic marine bacteria that put oxygen into our atmosphere. Algae are eukaryotic, not bacteria. Vibrios are a category of prokaryotes based on their incomplete spiral shape but are not photosynthetic. Mycoplasmas are heterotrophic, not autotrophic, prokaryotes.<\/p>\n<\/section>\n<h3>Setting Boundaries<\/h3>\n<p><strong>Eukaryotes<\/strong> are characterized by their membrane-bound nucleus and organelles, and the chromosomes that carry their DNA. The first eukaryotes evolved about 1.5 billion years ago (for the previous 3 billion years, the world belonged to prokaryotes). The evolutionary step from prokaryotes to eukaryotes was one of the most revolutionary events in the biological history of the Earth.<\/p>\n<p>One widely supported theory, the <abbr title=\"a generally accepted theory about the origins of two organelles of eukaryotic cells: mitochondria and chloroplasts. These formerly free-living prokaryotic organisms came to live inside eukaryotic cells as endosymbionts serving to synthesize energy and photosynthesize.\">endosymbiotic theory<\/abbr>, suggests that mitochondria were once free-living bacteria that had developed the ability to use oxygen and make ATP. This conferred such an evolutionary advantage that these bacteria thrived and eventually evolved into aerobic bacteria. It is believed that over time these ATP-producing organisms became incorporated into larger cells, perhaps through ingestion. A prokaryote that incorporates into itself an ATP-generating cell gains a definite energetic, and evolutionary, advantage. Similarly, a large nonphotosynthetic prokaryote that ingests a photosynthetic prokaryote (a proto-chloroplast) also has a survival advantage. The fact that mitochondria have their own very prokaryote-like, single-strand DNA, and that their RNA and ribosomes closely resemble those of prokaryotes supports this theory further.<\/p>\n<p>Single-celled eukaryotes are mostly classified as Protists, which includes algae, slime molds, and protozoa.<\/p>\n<\/section>\n<p><!-- CONTENT ENDS HERE --><\/p>\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/discovering-cells\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/biochemistry-cell-biology\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/general-science\/cells-pieces-and-parts\">Next Lesson \u27a1<\/a><\/div>\n<p><a class=\"backtotop\" href=\"#title\">Back to Top<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u2b05 Previous Lesson\u00a0Workshop Index\u00a0Next Lesson \u27a1 Prokaryotes Objective In this lesson, we will review prokaryotes. Early Earthlings The first organisms to live on Earth were probably primitive prokaryotes\u2014the earliest form of simple, single-celled organisms. Archaea are the oldest known living things and are grouped in their own domain. Although there is still debate about what [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-135","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/pages\/135","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/comments?post=135"}],"version-history":[{"count":6,"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/pages\/135\/revisions"}],"predecessor-version":[{"id":648,"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/pages\/135\/revisions\/648"}],"wp:attachment":[{"href":"https:\/\/americanboard.org\/Subjects\/general-science\/wp-json\/wp\/v2\/media?parent=135"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}