We are headed towards computing a probability of life coming about by random chance. But before we do that, we have been looking at the complexity of what goes on at the most fundamental levels of the cell, the smallest complete unit of life. If we are going to compute the odds like a bookie would, we must properly handicap the "teams playing the game". So, we continue this study of what it takes to make a single protein in this post.
Proteins are made inside the cell with an amazing array of robotic machines. The first process is called transcription which starts inside the nucleus of the cell where the DNA is located. A pair of fancy protein robotic machines called helicase and polymerase unwind a section of the DNA for a particular gene and create a strand of messenger RNA (mRNA in blue) utilizing spare RNA nucleotides floating around in the nucleus. An RNA molecule is essentially one half of a section of the DNA strand. This mRNA is what specifies the code for a single protein. RNA is like a copy made for temporary use, much like a contractor makes a copy of the blueprint for use in the field on a building project. Now that the mRNA is made, it moves from inside the nuclear membrane through a gateway into the cytoplasm of the cell. At the same time, two other strands of RNA are made via a similar transcription process from the DNA. These strands of RNA are folded up into a machines called transfer RNA (tRNA) and ribosomal RNA (rRNA). Together they make up another molecular device called a ribosome (green) which is responsible for building the protein.
Now that all the parts are outside the nucleus but still inside the cell proper, the process of Translation begins. The mRNA strand is divided into sets of three nucleotides called codons. The ribosome is like a reading head on a tape player and is able to feel the shape of the codons by using the anticodons of the tRNA molecules. An anticodon contains the sequence of the complementary pairs of nucleotides corresponding to the codon. Each tRNA molecule is able to carry a particular one of twenty different amino acids (in pink). One tRNA molecule is responsible for selecting the next amino acid in sequence and the second tRNA molecule is responsible for hooking the amino acid to end of the resulting polypeptide chain which becomes a protein. The rRna molecule becomes the fixed part of the ribosomal unit which slides along the entire length of the mRNA molecule stopping at the end where it completes building the protein.
The protein is then able to fold up into its functional form to begin its role in making up the parts of the body such as skin, muscle, hair or other tissues. By the way, the inside of the cell is filled with a gelatinous fluid called cytoplasm. This process would not function in water. This makes the need for a cell membrane to protect the entire process from the outside environment a critical part for the entire system to operate.