What type of nucleic acid can be found in viruses

Deoxyribonucleic acid DNA encodes the information the cell needs to make proteins. A related type of nucleic acid, called ribonucleic acid RNA , comes in different molecular forms that participate in protein synthesis. So they're actually made of polymers of strings of repeating units, and the two most famous of the nucleic acids, that you've heard about, are DNA and RNA.

And nucleic acids in the cell act to actually store information. The cell encodes information, much like you recorded on a tape, into nucleic acids. Each capsomer is composed of one to six molecules of polypeptide, usually of the same kind homopolymers but sometimes different heteropolymers. Capsomers from the vertices and the faces are usually composed of different polypeptides.

A few viruses have a double capsid, each being composed of a different set of polypeptides. Other proteins, invariably glycoproteins, make up the peplomers projecting from the envelope; a second type of envelope protein is the nonglycosylated matrix protein that occurs as a layer at the inner surface of the lipid envelope of orthomyxoviruses, paramyxoviruses, and rhabdoviruses. One or more of the proteins on the surface of the virion has a specific affinity for complementary receptors present on the surface of susceptible cells; the same viral protein contains the antigenic determinants against which neutralizing antibodies are made.

Virions of several families carry a limited number of enzymes, transcriptases being the most important Table As a consequence, the composition of lipids of particular viruses differs according to the composition of the membrane lipids of the cells in which they have replicated.

The poxviruses, ranaviruses, and African swine fever virus contain cellular lipid in their envelopes, and other lipids in the inner part of the virion. Lipid occurs in the outer membrane of poxviruses, and has a different composition from that of host cell lipids. In ranaviruses and African swine fever virus the additional viral lipid occurs within the icosahedral capsid.

Apart from that associated with viral nucleic acid, carbohydrate occurs as a component of viral glycoproteins, which usually occur as peplomers, with their hydrophobic ends buried in the lipid bilayer of the envelope, while their glycosylated hydrophilic ends project into the medium. Poxviruses also contain internal glycoproteins, in the membrane of the core, and one of the outer capsid proteins of rotaviruses is glycosylated. In general, viruses are more sensitive than bacteria or fungi to inactivation by physical and chemical agents.

A knowledge of their sensitivity to environmental conditions is therefore important for ensuring the preservation of the infectivity of viruses as reference reagents, and in clinical specimens collected for diagnosis, as well as for their deliberate inactivation for such practical ends as sterilization, disinfection, and the production of inactivated vaccines see Chapter 14 and Chapter The principal environmental condition that may adversely affect the infectivity of viruses in clinical specimens is too high a temperature; other important conditions are pH and lipid solvents.

Viruses vary considerably in heat stability. At ambient temperature the rate of decay of infectivity is slower but significant, expecially in hot summer weather or in the tropics in any season.

The enveloped viruses are more heat labile than nonenveloped viruses. Some enveloped viruses, notably respiratory syncytial virus, tend to be inactivated by the process of freezing and subsequent thawing, probably as a result of disruption of the virion by ice crystals.

This poses problems in the collection and transportation of clinical specimens. The most practical way of avoiding such problems is to deliver specimens to the laboratory as rapidly as practicable, packed without freezing, on ice see Chapter In the laboratory, it is often necessary to preserve stocks of viable virus for years.

Freeze-drying prolongs viability significantly even at ambient temperatures, and is important in enabling live viral vaccines to be used in tropical countries. On the whole, viruses prefer an isotonic environment at physiological pH, but some virions tolerate a wide ionic and pH range. For example, whereas most enveloped viruses are inactivated at pH 5—6, adenoviruses and many picornaviruses survive the acidic pH of the stomach. The infectivity of enveloped viruses is readily destroyed by lipid solvents such as ether or chloroform, or detergents like sodium deoxycholate, so that these agents must be avoided in laboratory procedures concerned with maintaining the viability of viruses.

On the other hand, detergents are commonly used by virologists to solubilize viral envelopes and liberate proteins for use as vaccines or for chemical analysis.

Sensitivity to lipid solvents is also employed as a preliminary screening test in the identification of new viral isolates, especially by arbovirologists. National Center for Biotechnology Information , U. Veterinary Virology. Published online Jun PAUL J. Copyright and License information Disclaimer.

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Publisher Summary Viruses are smaller and simpler in construction than unicellular microorganisms, and they contain only one type of nucleic acid—either DNA or RNA—never both. Open in a separate window. Viral Structure In the simpler viruses the virion consists of a single molecule of nucleic acid surrounded by a protein coat, the capsid; the capsid and its enclosed nucleic acid together constitute the nucleocapsid.

PLATE Helical Symmetry The nucleocapsids of several RNA viruses have a different type of symmetry: the capsomers and nucleic acid molecule s self-assemble as a helix Fig. Nucleic Acid Any particular virus contains only a single kind of nucleic acid.

DNA The genome of all DNA viruses consists of a single molecule, which is double-stranded except in the case of the parvoviruses, and may be linear or circular. Protein Some virus-coded proteins are structural, i. Carbohydrate Apart from that associated with viral nucleic acid, carbohydrate occurs as a component of viral glycoproteins, which usually occur as peplomers, with their hydrophobic ends buried in the lipid bilayer of the envelope, while their glycosylated hydrophilic ends project into the medium.

Temperature Viruses vary considerably in heat stability. Ionic Environment and pH On the whole, viruses prefer an isotonic environment at physiological pH, but some virions tolerate a wide ionic and pH range. Lipid Solvents The infectivity of enveloped viruses is readily destroyed by lipid solvents such as ether or chloroform, or detergents like sodium deoxycholate, so that these agents must be avoided in laboratory procedures concerned with maintaining the viability of viruses.

Morphology: virus structure. In: Brown F. Williams and Wilkins; Baltimore: Design principles in virus particle construction. In: Horsfall F. Lippincott; Philadelphia: Viral membranes. In: Fraenkel-Conrat H. Plenum Press; New York: Structures of viruses. In: Mahy B. Cambridge University Press; Cambridge: Part I. Structural analysis of animal virus genomes. CRC Press; Philadelphia: Support Center Support Center. External link. Please review our privacy policy.

Enzymes affecting interaction of virions with the host cell surface. Cleaves N-acetylneuraminic acid from surface polysaccharides. Enzymes transcribing the viral genome into mRNA a. Enzymes adding specific terminal groups to viral mRNA.

Viruses synthesizing mRNA in virions e. Enzymes for nucleic acid replication or processing. Retrovirus, orthomyxovirus, paramyxovirus, herpesvirus, adenovirus. Circular superhelical dsDNA see Plate Linear dsDNA with inverted terminal repeats and a covalently bound protein see Fig. Linear dsDNA; two unique sequences flanked by reiterated sequences; isomeric configurations occur see Fig. Linear dsDNA; both ends covalently closed, with inverted terminal repeats see Fig.

The virus obtains the lipid molecules from the cell membrane during the viral budding process. However, the virus replaces the proteins in the cell membrane with its own proteins, creating a hybrid structure of cell-derived lipids and virus-derived proteins. Many viruses also develop spikes made of glycoprotein on their envelopes that help them to attach to specific cell surfaces. Nucleic Acid - Just as in cells, the nucleic acid of each virus encodes the genetic information for the synthesis of all proteins.

While the double-stranded DNA is responsible for this in prokaryotic and eukaryotic cells, only a few groups of viruses use DNA. Most viruses maintain all their genetic information with the single-stranded RNA. There are two types of RNA-based viruses. In most, the genomic RNA is termed a plus strand because it acts as messenger RNA for direct synthesis translation of viral protein. A few, however, have negative strands of RNA.

In these cases, the virion has an enzyme, called RNA-dependent RNA polymerase transcriptase , which must first catalyze the production of complementary messenger RNA from the virion genomic RNA before viral protein synthesis can occur. The Influenza Flu Virus - Next to the common cold, influenza or "the flu" is perhaps the most familiar respiratory infection in the world.

In the United States alone, approximately 25 to 50 million people contract influenza each year. The symptoms of the flu are similar to those of the common cold, but tend to be more severe. Fever, headache, fatigue, muscle weakness and pain, sore throat, dry cough, and a runny or stuffy nose are common and may develop rapidly.

Gastrointestinal symptoms associated with influenza are sometimes experienced by children, but for most adults, illnesses that manifest in diarrhea, nausea, and vomiting are not caused by the influenza virus though they are often inaccurately referred to as the "stomach flu.

Since that time, a tremendous amount of research focusing upon the causative agent of AIDS has been carried out and much has been learned about the structure of the virus and its typical course of action. HIV is one of a group of atypical viruses called retroviruses that maintain their genetic information in the form of ribonucleic acid RNA.

The activity of the enzyme enables the genetic information of HIV to become integrated permanently into the genome chromosomes of a host cell. License Info. Image Use. Custom Photos. Site Info. Contact Us. The Galleries:. Photo Gallery.