DNA codes for life, but how?  It is the blue print for the chemicals that make up our body.  DNA tells the body what proteins to make which in turn carry out the functions of the cell, and form the structures of the cell.  How does DNA code for the proteins and what are proteins made of?  Proteins are made of Amino Acids which are bonded together in chains during transcription.  To determine what Amino Acids to bond together, certain enzymes have to "read" the DNA strands, construct an RNA strand that compliments the DNA strand, and then put together the Amino Acid chain.
 

DNA to RNA

    Remember the structure of DNA and chromosomes.  There are multiple genes on each DNA strand that spans the chromosome.  When the time comes to make a certain protein from the code of a certain gene, the cell does not need to read the whole DNA strand.  Instead, it only reads that gene, this being the most sensible thing to do.  There are a few enzymes that help this process to work.  The first of which are the Basal Factors which are a set of proteins that mark the promoter region or the beginning of the gene that is to be read.  The end of the gene is marked by the Enhancer Region with the Activator proteins (transcription factors).  From the promoter region and the enhancer region, transcription will take place.  The first step begins with the Bending protein traveling along the gene to a spot between the enhancer region and the promoter region.  Once at this halfway spot the protein bends the DNA strand so that the activator proteins at the enchancer region are toughing the basal factors at the promoter region.  This combining of the proteins stimulates RNA polymerase to do its work.

    RNA polymerase is an enzyme that more or less does the same thing that DNA helicase and polymerase do.  It begins at the Promoter Region of the gene and unzips the DNA strand.  Next, it constructs a polynucleotide chain of RNA (ribonucleic acid) that compliments the DNA bases.  This enzyme pairs RNA nucleotides with the original DNA nucleotides with the rule of C=G and A=U.  U being Uracil takes the place of Thymine on the RNA strand that is forming.   As separate RNA nucleotides pair up with the bases of the DNA strand the enzyme bonds them into an polynucleotide chain of messanger RNA (mRNA).  When the RNA polymerase is finished, it drags the mRNA strand away from the DNA strand outside of the nucleus of the cell into the cytoplasm while the DNA strand "zips" up to its original form.
 

Introns

    Scientists have determined that up to 70 percent of the RNA that is made through transcription by copying DNA is unneeded.  One term for this unneeded DNA is "Junk DNA".  It is not known why there is so much junk DNA, but it possibly could lower the chances of mutations in the DNA sequence that could cause a disease, or a deformity.  This could be true since the mutations have a greater chance of happening to the junk DNA since there is more of it.  Since there is so much "Junk DNA" in the mRNA strand, it needs to be removed so the correct protein can be assembled.  As the mRNA is taken into the cytoplasm of the cell, an enzyme called a spliceosome runs along the polynucleotide chain to determine what part of the DNA strand should be cut out and discarded.  A string of unnecessary mRNA is called an intron.  When the sliceosome finds an intron it pulls the RNA together so that the intron loops away from the strand.  Then it cuts out the intron and bonds the two ends together.  Once the introns are cut out of the mRNA it is taken into the cytoplasm to undergo the last stage of transcription, protein synthesis.
 

Protein Synthesis

    Once the mRNA is outside of the nucleus, the protein is made.  A special component of the cell called a Ribosome runs along the strand to determine which amino acids to bond together to make a protein.  The ribosome reads every base in groups of three.  These groups are called codons.  Thus, a codon could be ACG, UGA, etc.
 

Anti-codons

    Changing focus.  There is a different kind of RNA called tRNA or transfer RNA.  Transfer RNA units are simple because they are made of RNA which is attached to a certain amino acid.  On these units of tRNA a special group of three bases distinguish what amino acid is attached to it.  This special group of three bases is called an anti-codon because the ribosome pairs up anti-codons with codons.  Each anti-codon is the exact compliment of bases as its codon.  For example:
 
Codons GAC UCC CGG UAU
Anti-codons CUG AGG GCC AUA
 

Ribosome

    Back to the ribosome.  As the ribosome runs along the mRNA strand, it reads the codons.  When the ribosome comes to the codon, AUG, it places its matching anti-codon next to it and uses the amino acid, methionine, that accompanies this anti-codon as the first amino acid in the amino acid chain.  Then it reads the next codon and the procedure is repeated, but it now bonds the first amino acid to the second one.  This process of reading the codons, matching them with their anti-codons, and bonding the amino acids together is continued until the ribosome reads a triplet of UAA, UAC, or UGA.  These codons tell the ribosome to stop bonding the amino acids together.  Once the Ribosome is finished bonding the amino acids together into what is called a polypeptide chain (not to be confused with polynucleotide chain), named because of the type of bond between the amino acids, the protein is finished being made and transcription is complete.
 
A Point to Remember
    AUG is the start codon which tells the ribosome to begin making the polypeptide chain.  UAA, UAC, and UGA are stop codons which tell the ribosome to stop making the polypeptide chain.


 
 

Links

DNA: Structure and Function
            DNA the Code of Life
            Nucleic Acids
            Replication