Prions and Other Infectious Agents

Welcome Back! A year of research under my belt, and I’m back to answer some more GRE questions. Here’s today’s:

An infectious agent that appears to have no nucleic acid is a:
A) bacterium
B) bacteriophage
C) viroid
D) virus
E) prion

This is one of those basic fact-knowledge questions, although even if you don’t know the exact properties of everything on this list, you may be able to figure it out. So let’s get into what the question is asking.

What exactly is an infectious agent? An infectious agent is some sort of organism (we can debate whether a virus is a true organism later…) that invades another organism to utilize the host’s resources to some end. Pop culture types call these things “germs,” which is a term that encompasses anything that makes humans feel bad in some way.

Scientists have the annoying ability to break up these germs into like groups that act and infect in a particular way, which usually involves the anatomy, physiology and phylogeny of the organism. This question is basically testing your knowledge of microbial anatomy.

On to the second part of the question. What is nucleic acid? This is the “NA” portion of DNA or RNA. The D and R simply refer to the sugar groups attached to the nucleic acid. Most organisms have some sort of nucleic acid (either DNA, RNA or both) that they use to reproduce. After all, DNA is the blueprint for life. I say “most organisms” because as we get better and better at finding things, we’re noticing an exception to this rule. More on that in a moment.

Alright, so now that we know what the question is asking, how do answer it? This is simply a fact question, so you need to know a little bit about these organisms. Let’s start with bacteria.

Bacteria are single celled organisms that have a cell wall and the ability to live free. Most people know about bacteria after a trip to the doctor and a filled prescription for antibiotics. The main thing you need to know, though, is these organisms reproduce by DNA, and therefore have nucleic acid.

Viruses are also single celled organisms (although here is where every biologist begins the “what is an organism?” debate) that is rather simple–they consist of some proteins and DNA or RNA. In order to do any biological process, they must invade a host cell and take over the cell’s functions. So, while simple, these still have nucleic acid, else they wouldn’t be able to take cells hostage.

Bacteriophages are much like viruses–in fact, they are a form of virus that infects specifically bacteria (hence the “bacterio” portion of the name). Just like other viruses, these are made of protein and DNA or RNA, and they take over a cell’s function inorder to reproduce. Did you catch that? They have nucleic acid.

Viroids are along the same line, and just like the name suggests, are a lot like viruses. These are specifically plant pathogens, consisting of circular RNA and protein. Once again, an organism with nucleic acid.

That leaves prions. This is one of those things I alluded to earlier–a new form of what may be an organsim or may not, that causes infection. A prion is misfolded protein that is able to act as an infectious agent. That’s pretty much all we know about it now. We don’t know how it reproduces (because it doesn’t have DNA or RNA!) nor do we know how it forms. There has been a lot of researhch into prions lately, as people are beginning to think these buggers are responsible for a variety of nasty diseases. The biggest problem is because we have so little knowledge about the prion, we don’t know how exactly they are spread, or how to stop them. Ah, the mysteries of medicine.

So our answer is D, prions.

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