A
nucleotide is like this:
The nitrogenous base (green) is variable - the others are constant. IE, the sugar (pink) is always ribose for RNA, and always deoxyribose for DNA. A phosphate (purple) is just a phosphate group.
A
nucleoside is the nitrogenous base (green) + sugar, a
nucleotide is base + sugar + phosphate, and a base is the nitrogen-containing single or double ring that points into the DNA helix, pairing with the one on the opposite strand.
There are four kinds of bases in DNA:
Note how they are labelled as Adenine, Cytosine, Guanine and Thymine.
(RNA uses
uracil (sorry, can't seem to put in as a pic) instead of thymine, and since the sugars are riboses instead of deoxyriboses, the "bases" are called ribonucleotides and are adenosine 5'-triphosphate, guanosine 5'-triphosphate, cytidine 5'-triphoshate and uridine 5'-triphosphate ... but normally, in an RNA molecule, just referred to as adenine, guanine etc - or just AUCG.)
DNA is a very long string of these bases, which pair A-T and C-G like so:
The two strands of DNA are antiparallel (ie one runs up and the other down), and coil into a helix.
The sequence of nucleobases is the
genetic code that you hear about. The sequence is
transcribed onto RNA, making a reverse, complementary strand: the DNA double-helix opens up so that free-floating ribonucleotides can come in and form a complementary strand. The RNA strand is then
translated by ribosomes into a sequence of amino acids to make a protein. Since there are only four bases, and you want a variety of proteins, the bases are read in threes - triplets - with a set amino acid for each individual
codon of three.
This figure explains how the RNA is translated: the RNA codon UCA would give you Ser. The ribosomes just throw in amino acids in the matching configuration, sticking them together to form a protein chain. The codon AUG doubles for a START signal.
Amino acids are what make up
proteins; proteins are the main structural and functional molecules in biology. They have this basic structure:
The R group is variable again: there are 20 commonly occuring natural amino acids.
Proteins are formed by the
condensation of many amino acids - they bond together in a long chain.
A
polypeptide is just a long chain of peptides - ie, a protein.
For more info on protein structure, read the Folding@Home links in my sig!
Mutations arise when the DNA is damaged, incorrectly copied or incorrectly repaired. In non-coding regions (junk DNA etc), this may have no effect - but in an actual gene, or a regulatory region, it may well change things. If one base is substituted for another base, you may get just a change of one amino acids in one protein; or there may be no effect. If a base is added in, or removed, then it will snarl up a whole sequence of amino acids, giving a different protein. This protein may be non-functional, or have its function affected positively or negatively - or it may do something else intirely.
Beautiful!
to be honest we know there are some holes out there that need a little clarity, but there hardly big enough to destroy the theory they are just based on things we don't know or can only guess at, not exactly holes more conjectural inconsistencies.
