DNA is not all the nucleic acid material there is in a cell. There are other acids involved in making the body work.
In addition to DNA, there is a major form of nucleic acid that is as important as DNA to the cell. This molecule is called RNA. RNA stands for ribonucleic acid. There are two forms of RNA that play very important roles in protein synthesis. These are called mRNA and tRNA. mRNA is messenger RNA and tRNA stands for transfer RNA.
This is probably all very confusing to you now. mRNA? tRNA? What do they have to do with genetics? Don't worry, you're not expected to know this yet. This level explains it all.
You see, DNA can never leave the nucleus. It's much too big for that. Imagine your computer as the nucleus and the world to be the rest of the cell. Say you have written a novel and saved it on your hard drive. Would you remove the hard drive, with programs, games, pictures, and all sorts of other unnecessary imformation on it, and take it to a publisher? No! Of course not. You'd get some disks and transfer just the novel onto them. This is the same with DNA. DNA contains all the information needed to make you. If your liver cells needed to produce a chemical, they don't need all the DNA instructions telling them how to make eyelashes, fingernails, and other things. All they want is the one gene that tells them how to make that chemical.
This, however, is more difficult than it seems. DNA cannot just break off the needed portion and send it to the cell's factory. It needs a more efficient way of getting the data out of the nucleus.
RNA is the answer to the problem. RNA is very similar to DNA in most ways,
but they do have some minor differences. For one, the five-carbon sugar in DNA,
deoxyribose, has one less oxygen atom than in RNA's five-carbon sugar, ribose. 
Another difference is the
fact that RNA is single stranded, not double stranded like DNA. Finally, there
is a difference in the bases that RNA employs. Recall that DNA's four bases are
adenine, thymine, guanine, and cytosine. These hold true for RNA, except for
thymine. Thymine is replaced by uracil, which
is represented by U, so instead of having A-T, we have A-U. You might be
thinking: Why would there be a need for A-U? Isn't RNA single stranded? There
wouldn't be any base-pairs! Actually, you'd be half right. RNA, by itself, is
single stranded. But it must be formed somehow. You then probably know more
about how it is formed than you think.
RNA is formed from DNA. The process is actually quite similar to DNA replication, only there is one additional mRNA strand produced, instead of another DNA double helix. Here's how it works.
Just like in DNA replication, the double helix unwinds and unzips. The two
strands of DNA are now separate. Another enzyme 
called RNA
polymerase goes along one of the DNA strands and, just like in DNA
replication, puts in the appropriate base pair nucleotides. Only, this time, RNA
nucleotides are put in instead of DNA nucleotides. After the gene is transcribed
onto the mRNA, the two DNA strands rejoin, and the mRNA goes on to its next
step.
Our mRNA needs to go through another series of processes before leaving the nucleus. mRNA has to mature. A special head nucleotide is attached to the top of the molecule, and a tail of as many as 200 nucleotides is also attached. We think the head allows the mRNA to bind with parts of the cell factory later in protein synthesis, but the function of the tail isn't very clear. After this maturing process, the mRNA strand is ready to see the world outside the nucleus.
The mRNA travels out of the nuclear pores and travels to the assembly line of
the cell: the ribosomes.
This is
where the exciting process of protein synthesis occurs. We won't get into that
just yet, but we will talk about some components of it so you will understand it
more easily.
There is another form of RNA: tRNA. tRNA is like mRNA in some ways, and
completely different in others. tRNA, like mRNA, is made of a ribose "backbone",
with the four bases A, U, C, G. However, it is not a long, flowing strand like
mRNA. It twists back upon itself in kind of a "t" shape. Look at 
the illustration. The tRNA holds
itself in this position by base-pairing with itself! tRNA also differs in its
role, which will be discussed more thoroughly in Level 4. However, tRNA will
eventually line some of its base pairs with mRNA. That's enough for information
on mRNA! Good luck on your quiz, and I will see you next level.
The Cosmic SerpentThe Cosmic Serpent is a personal adventure, a fascinating study of anthropology and ethnopharmacology, and a revolutionary look at how intelligence and consciousness may come into being. In a first-person narrative of scientific discovery that open new perspectives on biology, anthropology, and the limits of rationalism. Jeremy Narby reveals how startlingly different the world around us appears when we open our minds to it.
The Healers Handbook: A Journey Into Hyperspace penetrates the secrets of creation through the mysterious principles of DNA, the biological interface between spirit and matter which determines our actual physical characteristics and maladies.
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