Manufacturing of a raw protein: stop signals & a postal address

 I lay my hand on my mouth. Job 40:4

"The manufacturing of a raw protein is nothing short of an engineering miracle. The cell starts with a complex machine called a ribosome. This is composed of multiple proteins and RNAs, each of which must be coded in the DNA, manufactured with ATP-dependent processes … you get the drill.

*The mRNA is fed into the ribosome from one end. 

*The mRNA will be translated into protein three letters at a time. 

*Each set of three letters is called a ‘codon’. There are 64 possible codons and 21 amino acids, so some amino acids are ‘coded’ by more than one codon. 

*Three of the codons are used as ‘stop’ signals, but one of them can also code for the amino acid selenocysteine.

A series of adaptor molecules called transfer RNAs (tRNA) enter the ribosome. 

*At the base of each tRNA is a three-letter ‘anti-codon’ that matches a codon. 

*At the top of each tRNA is an amino acid that is removed from the tRNA and added to the growing protein strand. 

*Each tRNA is ‘charged’ with its amino acid by a specific protein in the aminoacyl transferase family. There are elaborate mechanisms to make sure the right amino acid is charged, not the wrong one, even if chemically similar. Not only do these proteins require ATP in their manufacture, but the charging step and the protein elongation step

also burn ATP.

Most proteins, if left to themselves, will fold up into a useless knot of random coils. Thus, they need help folding. After the strand leaves the ribosome, helper proteins called chaperones clamp onto the unfolded strand. 

*The protein is then escorted to, and inserted into, a huge multi-protein molecule called a chaperonin. We’re not exactly certain what happens inside, but the chaperonin will fold the protein into its near-finished state and spit it out the other end. More proteins. More activity. More ATP burned.

The final stage in the manufacturing process is delivery. 

Proteins must be actively transported to the site where they are needed. To do that, the cell uses a kinesin protein. There are many different kinesin types, but the main one we need to know about is a slender molecule with two legs. Those legs literally walk along a microtubule (made of proteins that require ATP in their manufacturing, transport, and assembly). Each step requires one ATP. The package to be delivered is stored on the top end of the kinesin and various signals and modifications to it effectively serve as a postal address." 

CMI