Ebook Harrison’s infectious diseases (2/E): Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Ebook Harrison’s infectious diseases (2/E): Part 2
Ebook Harrison’s infectious diseases (2/E): Part 2
SECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2e proteins. Some viruses also have an outer-membrane envelope. viruses arc obligate intracellular parasites: they can replicate only within cells since their nucleic acids do not encode tlie many enzymes necessary tor protein, carbohydrate, or lipid metabolism and tor the generation OÍ high-energy p Ebook Harrison’s infectious diseases (2/E): Part 2hosphates. Typically. viral nucleic acids encode proteins necessary for replicating and packaging the nucleic acids within the biochemical milieu of hEbook Harrison’s infectious diseases (2/E): Part 2
ost cells.viruses differ from virusoids, viroids. and prions. riruandt arc nucleic acids that depend on helper viruses to package their nucleic acids SECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2l, and are replicates! by cellular RNA polymerase II Priom (Chap. 104) are abnormal protein molecules that can spread, reproducing by changing the structure of their normal cellular protein counterparts. Prions have been implicates! in neurodegenerative conditions such as Creutzfeldt-Jakob disease. Ebook Harrison’s infectious diseases (2/E): Part 2Gerstmann-Straussler disease, kuru, and human bovine spongiform encephalopathy (“mad cow disease"’).VIRAL STRUCTUREa aipsid. Because of the limited geEbook Harrison’s infectious diseases (2/E): Part 2
neric complexity of viruses, then capsids are usually composed of multimers OÍ identical capsorneres. Capsomeres arc in turn composed of one ora few pSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2. while helical structures have only a twofold axis of symmetry. The entire structural unit of nucleic acid, nucieoproreints). and capsid is called a Hitdeowpsid.Many human viruses are composed simply of a core and a capsid. For these viruses, the outer surface of the capsid medialei contact with un Ebook Harrison’s infectious diseases (2/E): Part 2infected cells. Other viruses are more complex and have an outer hpid-containing envelope der.ved from virus-modified membranes of the infected cell.Ebook Harrison’s infectious diseases (2/E): Part 2
The piece of infected-cell membrane that becomes the viral envelope has usually been modified during infection by the insertion of virus-encoded glycoSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2e envelope in many enveloped viruses. In general, enveloped viruses are sensitive to lipid solvents and nonionic detergents that can dissolve the envelope, while viruses that consist only Of nucleocapsids are somewhat resistant. A schematic diagram for large and complex herpesviruses is shown in Fig Ebook Harrison’s infectious diseases (2/E): Part 2. 82 I. Prototypical pathogenic human viruses are listed in I able 82 1. The relative sizes and structures of typical pathogenic human viruses are shoEbook Harrison’s infectious diseases (2/E): Part 2
wn in Fig. 82 2.Viral genomes consist of (1) a single-strand or double-strand DNA. (2) a single-strand sense RNA, (3) a single-strand or segmented antSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2 can be translated directly into protein, whereas antisense RNAs must be copied into translatable RNA. Sense and antisense genomes are also referred to as poiitive-itrand and negative-strand genomes, respectively. Viral nucleic acid is usually associated with one or more virus-encoded nucleoproteins Ebook Harrison’s infectious diseases (2/E): Part 2 in the core of the viral particle. The viral nucleic acid and nucleoproteins are almost always enclosed in a protein shell called758TAXONOMY OF PATHOEbook Harrison’s infectious diseases (2/E): Part 2
GENICHUMAN VIRUSESAs is apparent from Table 82-1 and Fig. 82-2. the classification of viruses into orders and families is based on nucleic acid composSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2morphologically indistinguishable ill electron micrographs. Further subclassification into genera depends on similarities in epidemiology, biologic effects, and nucleic acid sequence.FIGURE 82-1Schematic diagram of an enveloped herpesvirus with an icosahedral nucleocapsid. The approximate respective Ebook Harrison’s infectious diseases (2/E): Part 2 dimensions of the nudeocapsid and the enveloped particles arc 110 and 180 nm. The capsid is composed ol 162 capso-rncrcs: 150 with sixfold and 12 witEbook Harrison’s infectious diseases (2/E): Part 2
h fivefold axes ol symmetry.Most human viruses have a common name related to their pathologic effects or the circumstances of their dis-coven-. FormalSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2wed by the family or genus of the virus and a number. This dual terminology can cause confusion when viruses are referred to and referenced by either name e.g., varicella-zoster virus (V/.V) or human herpesvirus (HHV)3.VIRAL INFECTION IN VITROSTAGES OF VIRAL INFECTIONAT THE CELLULAR LEVELViral Inter Ebook Harrison’s infectious diseases (2/E): Part 2actions with the cell surface and cell entryAll viruses must overcome the barrier posed by the cell’s plasma membrane in order to deliver their payloaEbook Harrison’s infectious diseases (2/E): Part 2
d of nucleic acid into the cell. Infection is initiated by attachment of the virus to the cell surface. Various cellular proteins, carbohydrates, and SECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2ough relatively weak or nonspecific interactions with vữal surface proteins. Higher-affinity binding of viral surface proteins to specific cell-surface proteins, or receptors (see Table 2-1), is more critical for viral infection" Receptor binding is often augmented by interaction of viral surface pr Ebook Harrison’s infectious diseases (2/E): Part 2oteins with other cell- surface proteins, or co-receptors. important for various aspects of virus entry. Receptors and co-receptors are important deteEbook Harrison’s infectious diseases (2/E): Part 2
rminants of the cell types and species that a virus can infect. For example, the HIV envelope glycoprotein binds to the T cell surface protein CD4 andSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2 B lymphocyte complement receptor CD21 and 759 then Uses major histocompatibility complex (MHC) class II molecules as a co-receptor.Viruses use different strategies to penetrate the cell membrane. Some enveloped viruses use membrane fusion to deliver their contents into the cytoplasm. In general, a Ebook Harrison’s infectious diseases (2/E): Part 2trigger (e.g.. receptor binding) induces a conformational change that allows the viral surface protein to extend into the cell membrane, bringing theEbook Harrison’s infectious diseases (2/E): Part 2
virus and cell membrane into close proximity and thereby enabling fusion and formation of a pore through which the viral nucleocapsid can re be deliveSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2ed by s endocylosis. The low pH in endosomes can trigger viral 2. membrane or capsid fusion with the endocytic membrane. Conformational changes in nonenveloped capsids can lead to endosomal membrane penetration and release of viral nucleic acid into the cytoplasm.Influenza virus provides a well-stud Ebook Harrison’s infectious diseases (2/E): Part 2ied example of the effect of low pH on viral penetration. Influenza hemagglutinin mediates adsorption, receptor aggregation. and endocytosis. In low-pEbook Harrison’s infectious diseases (2/E): Part 2
n endosomes, changes in conformation of the hemagglutinin expose amphipathic domains that interact chemically with the cell membrane and initiate fusiSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2an ion channel in the envelope.I he fusion of viral proteins with cell membranes is a crucial step in viral infection. The hydrophobic interactions required tor fusion can be susceptible to chemical inhibition or blockade, rhe HIV envelope glycoprotein gpizo is associated with gp41 on the viral surf Ebook Harrison’s infectious diseases (2/E): Part 2ace. Binding of inv gp!20 to CD4 and chemokine receptors results in a conformational change, allowing gp41 to initiate cell membrane fusion. EnfuvirliEbook Harrison’s infectious diseases (2/E): Part 2
de is a small-pcplide drug derived from gp41 that hinds to gp4l and prevents the conformational change requứed for fusion. Maravi-roc prevents virus eSECTION VVIRAL INFECTIONSCHAPTER 82MEDICAL VIROLOGYFred Wang ■ Elliott KieffDEFINING A VIRUSKirrnw consist of a nucleic acid surrounded by one or more Ebook Harrison’s infectious diseases (2/E): Part 2lease of viral nucleoprotein into the cytoplasm, the viral genome is transported to a site for expression and replication. In order to produce infectious progeny, viruses must (1) produce proteins necessary' to replicate then nucleic acid. (2) produce structural proteins, and (3) assemble the nuclei Ebook Harrison’s infectious diseases (2/E): Part 2c acid and proteins into progeny virions. Different viruses use different strategies and gene repertoires to accomplish these goals. DNA viruses, exceEbook Harrison’s infectious diseases (2/E): Part 2
pt for poxviruses, replicate then nucleic acid and assemble into nucleocapsid complexes in the cell nucleus. RNA viruses, except for influenza VitusesGọi ngay
Chat zalo
Facebook