Question

How does DNA code for proteins?

Answer 1

This is probably one of the most complex processes and rather difficult to explain in a short space.

An overview:
DNA =>RNA=>Protein
These are the steps:
Replication
Transcription
Translation

The DNA remains in the cell nucleus but the production of the protein occurs in the cytoplasm. This requires the help of mRNA. DNA has the code for a protein which mRNA has to copy and then take that copy out of the nucleus to an other organelle called a ribosome. There the copy is translated into the protein.

There are three types of RNA: mRNA, tRNA and rRNA.(ribosomal).

In translation, messenger RNA (mRNA) produced by transcription is decoded by a ribosome complex to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein using tRNA.

The ribonucleotides are "read" by translational machinery (the ribosome) in a sequence of nucleotide triplets called codons. Each of those triplets codes for a specific amino acid. These amino acids are "added" one by one to form a protein.