How proteins are made
D. Indumathi, The Institute of Mathematical Sciences, Chennai
We know that all living things are made of cells. Eucaryotic cells have a cell nucleus. The most important molecule in the nucleus is DNA. Deoxyribonucleic acid (abbreviated DNA) is the molecule that carries genetic information for the development and functioning of an organism. DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix. DNA is made up of repeating units called nucleotides. Each nucleotide in DNA is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, and a phosphate group.
Ribonucleic acid (abbreviated RNA) is a nucleic acid present in all living cells that has structural similarities to DNA. Unlike DNA, however, RNA is most often single-stranded. An RNA molecule has a backbone made of alternating phosphate groups and the sugar ribose, rather than the deoxyribose found in DNA.
The bases in DNA are (cytosine [C], guanine [G], adenine [A] or thymine [T]). The two chains of the double helix are bonded together by the bases: A on one leg bonds with T of the other, while G and C bond together (see figure). In contrast, RNA has uracil [U] instead of thymine.
RNA synthesis: trancription
RNA is made from DNA when the double strands open up and one of the strands is copied in a process called transcription. You can see in the figure that the RNA is a copy of one of the DNA strands, with orange U replacing red T. Synthesis of RNA needs the enzyme called RNA polymerase. This complicated looking protein opens up the DNA strands at the right place to produce the RNA that is needed. This RNA then leaves the nucleus and goes into the outer cytoplasm of the cell to synthesise (produce) proteins. It is called messenger RNA or m-RNA.

Protein Synthesis
Just like DNA was the template used to make RNA with the help of RNA polymerase, here mRNA is the template used to make proteins with the help of ribosomes. The ribosome has a large and small subunit. The ribosome traverses the mRNA three units (nucleotides) at a time. Three such units code for an amino acid, which are the building blocks of proteins. One at a time, these amino acids are formed and then these together form a chain of amino acids which form the protein that needs to be synthesised. This process is called translation. Every protein in your body is formed this way. Amazing, isn't it?
Images and text from several sources