Viruses

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006699" TEXT="#080000" bgproperties="fixed" background="02c285a1erlcgo.png"> <div> <FONT SIZE="5" COLOR="#FFCC66" FACE="Arial" ><B>Mr. Manning's Life Science Class</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="Mr. Mannings Life Science Class"><B>home</B></A></div> <div>                                                   </div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000" background="02ad2c00dkelyh.png"> <bR> </td> <td valign="top" height=390 width="100%" BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I> <A NAME="viruses"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></I><I>Viruses</I></div> <div> <B>When is a life form not a life form?</B> </div> <div> When it's a virus.   </div> <div>                                       <IMG SRC="8596e6a0.gif" border=0 width="110" height="106" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> Viruses are strange things that straddle the fence between living and non-living. On the one hand, if they're floating around in the air or sitting on a doorknob, they're inert. They're about as alive as a rock. But if they come into contact with a suitable plant, animal or bacterial cell, they spring into action. They infect and take over the cell like pirates hijacking a ship.</div> <bR> <div> <B>What They Are</B></div> <div> A virus is basically a tiny bundle of genetic material—either DNA or RNA—carried in a shell called the viral coat, or capsid, which is made up of bits of protein called capsomeres. Some viruses have an additional layer around this coat called an envelope. That's basically all there is to viruses. </div> <div> <TABLE BORDER="0" CELLPADDING="1" CELLSPACING="1" WIDTH="144" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="VOID" RULES="NONE" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=CENTER ROWSPAN=2 HEIGHT= 113 WIDTH="3"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="113" ALIGN="bottom" WIDTH="3" HSPACE="0" VSPACE="0"></tD> <tD VALIGN=CENTER><NOBR><div> <IMG SRC="85a836b0.gif" border=0 width="131" height="107" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> </NOBR></tD> </tR> <tR> <tD VALIGN=CENTER WIDTH="134"><div> Rotavirus</div> <div> Courtesy CDC</div> <bR> </tD> </tR> </TABLE></div> <div> <B>What They Look Like</B></div> <div> There are thousands of different viruses that come in a variety of shapes. Many are polyhedral <<I>polly-hee-drul</I>>, or multi-sided. If you've ever looked closely at a cut gem, like the diamond in an engagement ring, you've seen an example of a polyhedral shape. (Unlike the diamond in a ring, however, a virus does not taper to a point, but is shaped similarly all around.) Other viruses are shaped like spiky ovals or bricks with rounded corners. </div> <div> <TABLE BORDER="0" CELLPADDING="1" CELLSPACING="1" WIDTH="138" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="VOID" RULES="NONE" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=CENTER HEIGHT= 89 ><NOBR><div> <IMG SRC="85b7d530.gif" border=0 width="125" height="83" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> </NOBR></tD> <tD VALIGN=CENTER ROWSPAN=2 WIDTH="3"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="89" ALIGN="bottom" WIDTH="3" HSPACE="0" VSPACE="0"></tD> </tR> <tR> <tD VALIGN=CENTER HEIGHT= 52 WIDTH="128"><div> Ebola virus</div> <div> Courtesy CDC</div> <bR> </tD> </tR> </TABLE></div> <div> Some are like skinny sticks while others look like bits of looped string. Some are more complex and shaped like little lunar landing pods. </div> <bR> <div> <B>Where They're Found</B></div> <div> Viruses are found on or in just about every material and environment on Earth from soil to water to air. They're basically found anywhere there are cells to infect. Viruses have evolved to infect every form of life, from animal to plant and from fungi to bacteria. </div> <div> However, viruses tend to be somewhat picky about what type of cells they infect. Plant viruses are not equipped to infect animal cells, for example, though a certain plant virus could infect a number of related plants. Sometimes, a virus may infect one creature and do no harm, but cause havoc when it gets into a different but closely enough related creature. For example, the Hantavirus is carried by deer mice without much noticeable effect on the rodents. But if Hantavirus gets into a person, it causes a dramatic and frequently deadly disease marked by excessive bleeding.</div> <div> <TABLE BORDER="0" CELLPADDING="1" CELLSPACING="1" WIDTH="137" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="VOID" RULES="NONE" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=CENTER ROWSPAN=2 HEIGHT= 118 WIDTH="7"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="118" ALIGN="bottom" WIDTH="7" HSPACE="0" VSPACE="0"></tD> <tD VALIGN=CENTER><NOBR><div> <IMG SRC="85c7d700.gif" border=0 width="125" height="112" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> </NOBR></tD> </tR> <tR> <tD VALIGN=CENTER><NOBR><div> Type A flu virus</div> <div> Courtesy CDC</div> <bR> </NOBR></tD> </tR> </TABLE></div> <div> <B>Single-Minded Mission</B></div> <div> Viruses exist for one purpose only: to reproduce. To do that, they have to take over the reproductive machinery of suitable host cells. </div> <div> Upon landing on an appropriate host cell, a virus gets its genetic material inside the cell either by tricking the host cell to pull it inside, like it would a nutrient molecule, or by fusing its viral coat with the host cell wall or membrane and releasing its genes inside. Some viruses inject their genes into the host cell, leaving their empty viral coats sitting outside. </div> <div> If a virus is a DNA virus, its genetic material then inserts itself into the host cell's DNA. If the virus is an RNA virus, it must first turn its RNA into DNA using the host cell's machinery before inserting into the host DNA. The viral genes are then copied many, many times, using the machinery the host cell would normally use to reproduce its own DNA. The virus uses the host cell's enzymes to build new viral capsids and other viral proteins. The new viral genes and proteins then come together and assemble into whole new viruses. The new viruses are either released from the host cell without destroying the cell or eventually build up to a large enough number that they burst the host cell like an overfilled water balloon.</div> <div> <B>Other Virus-Like Things</B></div> <div> Viruses may be referred to often as the smallest infectious things. But there are some smaller contenders. Some of the agents of plant disease lack even a viral coat and are merely small strings of plain, or "naked," RNA. These particles are called <B>viroids</B>. They are believed to be a more primitive version of ordinary viruses. </div> <div> But maybe viroids aren't the smallest infectious agents all.</div> <div> <B>Prions</B></div> <div> Do you recall hearing about Mad Cow Disease? This is an ailment that affects the animals' brains and is also called bovine spongiform encephalopathy <<I>boh-vine sponge-ee-form en-sef-uh-la-puth-ee</I>> because it makes the brain appear holey, like a sponge. There is a human form of this disease called Creutzfeldt-Jakob <<I>kroits-feld ya-cob</I>> disease. Some scientists now believe these brain illnesses are among a few diseases caused by an infectious agents called <B>prions</B> <<I>pree-ons</I>>. Prions are not even DNA or RNA, but simply proteins. They are thought to be misshapen or abnormal versions of proteins normally found in animals or people. Very little is known about prions. Scientists suggest that they spread when a prion comes into contact with the normal version of the protein and causes the normal protein to change shape and become a prion, too. Click <A HREF="#all_about_prions" TITLE="Viruses"><B>All About Prions</B></A> to learn more details about prions.</div> <div> You can also find a lot more detailed information and several photos of viruses at  <A HREF="http://library.thinkquest.org/23054/gather/index.shtml" TARGET="_top" TITLE="http://library.thinkquest.org/23054/gath"><B>Hidden Killers: Deadly Viruses</B></A>. You'll find a great collection of virus portraits at <A HREF="http://www.tulane.edu/~dmsander/Big_Virology/BVHomePage.html" TARGET="_top" TITLE="http://www.tulane.edu/~dmsander/Big_Viro"><B>The Big Picture Book of Viruses</B></A>. </div> <bR> <div> <I> <A NAME="all_about_prions"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></I><I>All About Prions</I></div> <DIV ALIGN="LEFT"></DIV> <div> <IMG SRC="85df04d0.gif" border=0 width="496" height="77" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> Sometimes a scientific discovery shakes the confidence of scientists, making them question whether they truly understand nature's "ground rules." </div> <div> That's exactly what prions have done to scientists' understanding of the ground rules for infectious diseases. Prions cause diseases, but they aren't viruses or bacteria or fungi or parasites. They are simply proteins, and proteins were never thought to be infectious on their own. Organisms are infectious, proteins are not. Or, at least, they never used to be. </div> <div> Prions entered the public's consciousness during the mad cow epidemic that hit England in 1986. For decades, however, scientists had searched for unusual, atypical infectious agents that they suspected caused some puzzling diseases that could not be linked to any of the "regular" infectious organisms. One possibility was that slow viruses--viruses that spent decades wreaking havoc in their hosts--might be the culprits, and these putative viruses were not only leisurely about multiplying but also hard to isolate. Now researchers are coming around, albeit reluctantly, to accepting the shocking fact that naked proteins can be infectious. "More than one protein chemist has declared this to be insane--and yet this is precisely what is implied by a growing number of studies" was the way one news article put it (1). </div> <bR> <bR> <div> Prions (pronounced pree-ahns) enter cells and apparently convert normal proteins found within the cells into prions just like themselves. The normal cell proteins have all the same "parts" as the prions--specifically the same amino acid building blocks--but they <FONT SIZE="3" COLOR="#0000FF" FACE="Arial" ><U>fold differently</U></FONT>. They are much like the toy "Transformers" that intrigued little kids in the 1980s. A sphynx could become a robot; a bug could become a warrior. Nothing was added; nothing subtracted. </div> <div> <IMG SRC="85e4b8d0.gif" border=0 width="75" height="141" ALIGN="BOTTOM" HSPACE="0" VSPACE="0">      <IMG SRC="85f9e4b0.gif" border=0 width="158" height="75" ALIGN="BOTTOM" HSPACE="0" VSPACE="0">      <IMG SRC="860a6640.gif" border=0 width="166" height="100" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <bR> </td> </tr></table></body>