{"id":4854,"date":"2017-07-06T17:12:27","date_gmt":"2017-07-06T17:12:27","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/hccs-waymakerbiology1\/?post_type=chapter&#038;p=4854"},"modified":"2024-04-26T00:27:12","modified_gmt":"2024-04-26T00:27:12","slug":"viral-morphology","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/chapter\/viral-morphology\/","title":{"raw":"Viral Morphology","rendered":"Viral Morphology"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Discuss the basics of virus structure<\/li>\r\n<\/ul>\r\n<\/div>\r\nViruses are <strong>acellular<\/strong>, meaning they are biological entities that do not have a cellular structure. They therefore lack most of the components of cells, such as organelles, ribosomes, and the plasma membrane. Viruses are sometimes called <em>virions<\/em>: a virion is a 'complete' virus free in the environment (not in a host).\u00a0A virion consists of at least a\u00a0<strong>nucleic acid core <\/strong>and\u00a0an <strong>outer protein coating or capsid;\u00a0<\/strong>sometimes a virus will have an outer <strong>envelope<\/strong> made of protein and phospholipid membranes derived from the host cell. Viruses may also contain additional proteins, such as enzymes. The most obvious difference between members of viral families is their morphology, which is quite diverse. An interesting feature of viral complexity is that the complexity of the host does not correlate with the complexity of the virion. Some of the most complex virion structures are observed in <strong>bacteriophages<\/strong>, viruses that infect the simplest living organisms, bacteria.\r\n<h2>Types of Nucleic Acid<\/h2>\r\nUnlike nearly all living organisms that use DNA as their genetic material, viruses may use either DNA or RNA as theirs. The <strong>virus core<\/strong> contains the genome or total genetic content of the virus. Viral genomes tend to be small, containing only those genes that encode proteins that the virus cannot get from the host cell. This genetic material may be single- or double-stranded. It may also be <em>linear or circula<\/em>r.\r\n\r\nDNA viruses cause human diseases, such as chickenpox, hepatitis B, and some venereal diseases, like herpes and genital warts. Human diseases caused by RNA viruses include hepatitis C, measles, and rabies.\r\n<h2>Morphology<\/h2>\r\n[caption id=\"attachment_1141\" align=\"alignright\" width=\"332\"]<img class=\"wp-image-1141\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1648\/2017\/07\/06170614\/Figure_21_01_02.jpg\" alt=\"In the illustration a viral receptor on the surface of a KSHV virus is attached to an xCT receptor embedded in the plasma membrane.\" width=\"332\" height=\"328\" \/> Figure 1.\u00a0The KSHV virus binds the xCT receptor on the surface of human cells.\u00a0 (credit: modification of work by NIAID, NIH)[\/caption]\r\n\r\nViruses come in many shapes and sizes, but these are consistent and distinct for each viral family. All virions have a nucleic acid genome covered by a protective layer of proteins, called a <strong>capsid<\/strong>. The capsid is made up of protein subunits called <strong>capsomeres<\/strong>. Some viral capsids are simple polyhedral \u201cspheres,\u201d whereas others are quite complex in structure.\r\n\r\nMany viruses use some sort of glycoprotein to attach to their host cells via molecules on the cell called <strong>viral receptors<\/strong> (Figure 1).\r\n\r\nAmong the most complex virions known, the T4 bacteriophage, which infects the <em>Escherichia coli<\/em> bacterium, has a tail structure that the virus uses to attach to host cells and a head structure that houses its DNA.\r\n\r\nOverall, the shape of the virion and the presence or absence of an envelope tell us little about what disease the virus may cause or what species it might infect, but they are still useful means to begin viral classification (Figure 2).\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Question<\/h3>\r\n[caption id=\"attachment_1142\" align=\"aligncenter\" width=\"600\"]<img class=\"wp-image-1142\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1648\/2017\/07\/06170616\/Figure_21_01_03.png\" alt=\"Illustration a shows bacteriophage T4, which houses its DNA genome in a hexagonal head. A long, straight tail extends from the bottom of the head. Tail fibers attached to the base of the tail are bent, like spider legs. In b, adenovirus houses its DNA genome in a round capsid made from many small capsomere subunits. Glycoproteins extend from the capsomere, like pins from a pincushion. In c, the HIV retrovirus houses its RNA genome and an enzyme called reverse transcriptase in a bullet-shaped capsid. A spherical viral envelope, lined with matrix proteins, surrounds the capsid. Glycoproteins extend from the viral envelope.\" width=\"600\" height=\"436\" \/> Figure 2.\u00a0Viruses can be either complex in shape or relatively simple. This figure shows three relatively complex virions: the bacteriophage T4, with its DNA-containing head group and tail fibers that attach to host cells; adenovirus, which uses spikes from its capsid to bind to host cells; and HIV, which uses glycoproteins embedded in its envelope to bind to host cells. Notice that HIV has proteins called matrix proteins, internal to the envelope, which help stabilize virion shape. (credit \u201cbacteriophage, adenovirus\u201d: modification of work by NCBI, NIH; credit \u201cHIV retrovirus\u201d: modification of work by NIAID, NIH)[\/caption]\r\n\r\nWhich of the following statements about virus structure is true?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>All viruses are encased in a viral membrane.<\/li>\r\n \t<li>The capsomere is made up of small protein subunits called capsids.<\/li>\r\n \t<li>DNA is the genetic material in all viruses.<\/li>\r\n \t<li>Glycoproteins help the virus attach to the host cell.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"243497\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"243497\"]Statement d is true.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/efd2981a-d5de-42d2-ad67-fd447d531851\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Discuss the basics of virus structure<\/li>\n<\/ul>\n<\/div>\n<p>Viruses are <strong>acellular<\/strong>, meaning they are biological entities that do not have a cellular structure. They therefore lack most of the components of cells, such as organelles, ribosomes, and the plasma membrane. Viruses are sometimes called <em>virions<\/em>: a virion is a &#8216;complete&#8217; virus free in the environment (not in a host).\u00a0A virion consists of at least a\u00a0<strong>nucleic acid core <\/strong>and\u00a0an <strong>outer protein coating or capsid;\u00a0<\/strong>sometimes a virus will have an outer <strong>envelope<\/strong> made of protein and phospholipid membranes derived from the host cell. Viruses may also contain additional proteins, such as enzymes. The most obvious difference between members of viral families is their morphology, which is quite diverse. An interesting feature of viral complexity is that the complexity of the host does not correlate with the complexity of the virion. Some of the most complex virion structures are observed in <strong>bacteriophages<\/strong>, viruses that infect the simplest living organisms, bacteria.<\/p>\n<h2>Types of Nucleic Acid<\/h2>\n<p>Unlike nearly all living organisms that use DNA as their genetic material, viruses may use either DNA or RNA as theirs. The <strong>virus core<\/strong> contains the genome or total genetic content of the virus. Viral genomes tend to be small, containing only those genes that encode proteins that the virus cannot get from the host cell. This genetic material may be single- or double-stranded. It may also be <em>linear or circula<\/em>r.<\/p>\n<p>DNA viruses cause human diseases, such as chickenpox, hepatitis B, and some venereal diseases, like herpes and genital warts. Human diseases caused by RNA viruses include hepatitis C, measles, and rabies.<\/p>\n<h2>Morphology<\/h2>\n<div id=\"attachment_1141\" style=\"width: 342px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1141\" class=\"wp-image-1141\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1648\/2017\/07\/06170614\/Figure_21_01_02.jpg\" alt=\"In the illustration a viral receptor on the surface of a KSHV virus is attached to an xCT receptor embedded in the plasma membrane.\" width=\"332\" height=\"328\" \/><\/p>\n<p id=\"caption-attachment-1141\" class=\"wp-caption-text\">Figure 1.\u00a0The KSHV virus binds the xCT receptor on the surface of human cells.\u00a0 (credit: modification of work by NIAID, NIH)<\/p>\n<\/div>\n<p>Viruses come in many shapes and sizes, but these are consistent and distinct for each viral family. All virions have a nucleic acid genome covered by a protective layer of proteins, called a <strong>capsid<\/strong>. The capsid is made up of protein subunits called <strong>capsomeres<\/strong>. Some viral capsids are simple polyhedral \u201cspheres,\u201d whereas others are quite complex in structure.<\/p>\n<p>Many viruses use some sort of glycoprotein to attach to their host cells via molecules on the cell called <strong>viral receptors<\/strong> (Figure 1).<\/p>\n<p>Among the most complex virions known, the T4 bacteriophage, which infects the <em>Escherichia coli<\/em> bacterium, has a tail structure that the virus uses to attach to host cells and a head structure that houses its DNA.<\/p>\n<p>Overall, the shape of the virion and the presence or absence of an envelope tell us little about what disease the virus may cause or what species it might infect, but they are still useful means to begin viral classification (Figure 2).<\/p>\n<div class=\"textbox exercises\">\n<h3>Practice Question<\/h3>\n<div id=\"attachment_1142\" style=\"width: 610px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1142\" class=\"wp-image-1142\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1648\/2017\/07\/06170616\/Figure_21_01_03.png\" alt=\"Illustration a shows bacteriophage T4, which houses its DNA genome in a hexagonal head. A long, straight tail extends from the bottom of the head. Tail fibers attached to the base of the tail are bent, like spider legs. In b, adenovirus houses its DNA genome in a round capsid made from many small capsomere subunits. Glycoproteins extend from the capsomere, like pins from a pincushion. In c, the HIV retrovirus houses its RNA genome and an enzyme called reverse transcriptase in a bullet-shaped capsid. A spherical viral envelope, lined with matrix proteins, surrounds the capsid. Glycoproteins extend from the viral envelope.\" width=\"600\" height=\"436\" \/><\/p>\n<p id=\"caption-attachment-1142\" class=\"wp-caption-text\">Figure 2.\u00a0Viruses can be either complex in shape or relatively simple. This figure shows three relatively complex virions: the bacteriophage T4, with its DNA-containing head group and tail fibers that attach to host cells; adenovirus, which uses spikes from its capsid to bind to host cells; and HIV, which uses glycoproteins embedded in its envelope to bind to host cells. Notice that HIV has proteins called matrix proteins, internal to the envelope, which help stabilize virion shape. (credit \u201cbacteriophage, adenovirus\u201d: modification of work by NCBI, NIH; credit \u201cHIV retrovirus\u201d: modification of work by NIAID, NIH)<\/p>\n<\/div>\n<p>Which of the following statements about virus structure is true?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>All viruses are encased in a viral membrane.<\/li>\n<li>The capsomere is made up of small protein subunits called capsids.<\/li>\n<li>DNA is the genetic material in all viruses.<\/li>\n<li>Glycoproteins help the virus attach to the host cell.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q243497\">Show Answer<\/span><\/p>\n<div id=\"q243497\" class=\"hidden-answer\" style=\"display: none\">Statement d is true.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_efd2981a-d5de-42d2-ad67-fd447d531851\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/efd2981a-d5de-42d2-ad67-fd447d531851?iframe_resize_id=assessment_practice_id_efd2981a-d5de-42d2-ad67-fd447d531851\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-4854\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":10,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\"}]","CANDELA_OUTCOMES_GUID":"2ea35034-c826-45ff-8981-2448b680fbef, d834da6d-406b-4710-90d7-9643f855a89b","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4854","chapter","type-chapter","status-publish","hentry"],"part":297,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapters\/4854","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":11,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapters\/4854\/revisions"}],"predecessor-version":[{"id":6769,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapters\/4854\/revisions\/6769"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/parts\/297"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapters\/4854\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/wp\/v2\/media?parent=4854"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/pressbooks\/v2\/chapter-type?post=4854"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/wp\/v2\/contributor?post=4854"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology1\/wp-json\/wp\/v2\/license?post=4854"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}