I think I am going to stick on viruses again. Yesterday I gave you a sampling of just how many viruses there are on Earth. Today I am going to touch on just how diverse the world of viruses really is. As a teaser, it is probably much more diverse that you can probably imagine.
I'm sure everyone knows that the storage format for genetic information in humans is DNA. All of the genes you need to make a complex person is encoded in DNA, specifically double stranded DNA in a helical arrangement, packed into individual chromosomes. Every living thing on Earth, from the simplest bacteria to the humans encode information and store it in double stranded DNA. Viruses are a little more complex, and this hints that they are incredibly diverse and probably pre-date the universal double stranded DNA system in evolutionary history. How much more diverse? Well, there are certainly viruses that store their genetic information in double stranded DNA, just like everything else on Earth, but that is a small part of the diversity of viruses. You probably also know from a biology class sometime in your past that in humans DNA is made into single stranded messenger RNA, which can then be decoded into protein. Well, many viruses exist solely as single stranded messenger RNA, bypassing the need for DNA. Some of these viruses are 'positive sense' RNA, meaning they encode information that can be directly turned into proteins, but many others are 'minus sense' so they are nonsense when read, and first must be copied into a positive strand. Some viruses are DNA but are not double stranded, but only have a single strand. Others are partially double stranded and partially single stranded. Some are even RNA/DNA hybrids. If that isn't complicated enough, many viruses exist as multiple fragments of DNA or RNA rather than a single molecule.
To give you some idea of what this looks like in a picture, you can look at one classification scheme proposed by Dr. David Baltimore. All living things on Earth are similar to group I in this diagram in terms of the flow of genetic information being from DNA storage to mRNA to make proteins.
Here is a picture of the major classifications of viruses, grouped by type of genome and virion structure that represents the major virus families.
This hopefully gives some perspective in why a drug targeting one type of virus can't be used on all viruses, as well as an idea of just how different viruses can be from one another, and from the rest of the biosphere.
I'm sure everyone knows that the storage format for genetic information in humans is DNA. All of the genes you need to make a complex person is encoded in DNA, specifically double stranded DNA in a helical arrangement, packed into individual chromosomes. Every living thing on Earth, from the simplest bacteria to the humans encode information and store it in double stranded DNA. Viruses are a little more complex, and this hints that they are incredibly diverse and probably pre-date the universal double stranded DNA system in evolutionary history. How much more diverse? Well, there are certainly viruses that store their genetic information in double stranded DNA, just like everything else on Earth, but that is a small part of the diversity of viruses. You probably also know from a biology class sometime in your past that in humans DNA is made into single stranded messenger RNA, which can then be decoded into protein. Well, many viruses exist solely as single stranded messenger RNA, bypassing the need for DNA. Some of these viruses are 'positive sense' RNA, meaning they encode information that can be directly turned into proteins, but many others are 'minus sense' so they are nonsense when read, and first must be copied into a positive strand. Some viruses are DNA but are not double stranded, but only have a single strand. Others are partially double stranded and partially single stranded. Some are even RNA/DNA hybrids. If that isn't complicated enough, many viruses exist as multiple fragments of DNA or RNA rather than a single molecule.
To give you some idea of what this looks like in a picture, you can look at one classification scheme proposed by Dr. David Baltimore. All living things on Earth are similar to group I in this diagram in terms of the flow of genetic information being from DNA storage to mRNA to make proteins.
Here is a picture of the major classifications of viruses, grouped by type of genome and virion structure that represents the major virus families.
This hopefully gives some perspective in why a drug targeting one type of virus can't be used on all viruses, as well as an idea of just how different viruses can be from one another, and from the rest of the biosphere.
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