Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: thedoc on 24/09/2012 18:30:01

Title: What are the differences between DNA and RNA?
Post by: thedoc on 24/09/2012 18:30:01

ARCC asked the Naked Scientists:
   
Which are all the diferences between DNA and RNA?

What do you think?

Title: Re: What are the differences between DNA and RNA?
Post by: schneebfloob on 25/09/2012 09:18:40

DNA is deoxyribonucleic acid, whilst RNA is ribonucleic acid. They both contain a pentose sugar molecule. In DNA this is deoxyribose, and in RNA it is ribose. The difference here is that in deoxyribose in DNA there is no -OH group present on the second carbon of the sugar, which is found in ribose in RNA. OH groups are quite reactive and this makes RNA less stable than DNA, and more susceptible to degradation.

DNA and RNA both carry bases. In DNA these are: adenine, thymine, cytosine and guanine. In RNA thymine is not used, and uracil is used in its place.

DNA has 3 distinct conformations - A, B and Z. B is almost always the form that is being talked about in living organisms. DNA is a double stranded molecule and it adopts a helical conformation, the double helix. RNA on the other hand comes in many forms in living organisms.
We can talk about:

• mRNA. This is single stranded RNA. This is used to carry genetic information out of the nucleus and brings it to the ribosomes where it can be translated to form protein.
• tRNA. This has a weird 'clover leaf' shape and is used to read the mRNA to synthesise proteins.
• rRNA. This makes up a large proportion of the ribosomes and has a very complex structure. It is the rRNA that gives ribosomes their catalytic activity and enables protein synthesis.

   There are also lots of other RNAs, which start getting too numerous to mention, but mRNA, tRNA and rRNA are the big three.

I realise that may be confusing so I'll provide a little added context.
DNA -> RNA -> Protein.

DNA is a way of storing the information about all of the proteins in your body. Every 3 base pairs in your DNA is called a codon. Each codon codes for a particular amino acid. For example AAA, which is three adenines in a row, codes for the amino acid lysine. Proteins are made up of chains of amino acids, so lots of codons make up genes which code for lots of amino acids in a particular sequence that make up your protein.

The DNA stays in the nucleus, but all machinery (the ribosomes) needed to read the genetic code and synthesise the protein is found outside of the nucleus. So, the genetic code is transcribed into another form so it can move to the ribosomes. This form is the mRNA. tRNA is another RNA, and this is used to basically read the codons in the mRNA and bring in the correct amino acids for each codon. Gradually, as the mRNA is read, more and more amino acids are added to form a chain - the protein. DNA and RNA differ both structurally and functionally.

Sorry if I've gone off on a huge tangent, but I do hope that answers your question.