Give the Lord What He Wants: Protein Synthesis

For we are God’s fellow works; you are God’s field, God’s building.

1 Corinthians 3:9, Douay-Rheims

As we said in the last section, your genes carry the instructions for what sort of creature you are – what color your hair is, how tall you are, the shape of your nose. Your DNA looks like a simple ladder with about 3.2 million rungs that twists as it goes up, a shape known as a double helix. The outside of the ladder is made up of repeated sugar molecules and phosphates (phosphorus and oxygen). Each rung of the ladder is made up of a pair of nucleotides (the nucleic acid part of deoxyribonucleic acid), which come in four types: adenine (A), thymine (T), cytosine (C), and guanine (G). In DNA, the nucleotides always come in pairs, with A matched to T and C matched to G.

How can something so simple determine what you are like? After all, DNA is really just like a book. What can you do with a book? You can open and close the book, read it, copy it, and…that is about all you can do without destroying it or using it in a way that it is not intended. A book cannot make an apple pie or a car, although it can give you instructions for how to make them yourself. Similarly, DNA cannot make your hair red, but it does contain the instructions for how to do it.

The way things are done in your body is through proteins. Proteins do so many different jobs in your body, from giving hair its color to making your fingernails hard and strong to making copies of the DNA itself. If you want something done in a creature, proteins are likely the way to do it. Proteins, as you might recall, are made of amino acids – little round balls that join together like a pearl necklace to make a protein. There are many types of amino acids, and twenty of them usually go into making proteins. Each amino acid has its own personality, of sorts: some don’t like water while others love it, some are positive while others are negative. These characteristics cause the protein to twist and fold into a unique shape that allows it to do its job. So, choosing what amino acids goes into a protein determines what that protein does, and do you know who chooses those amino acids? The DNA! But, it’s kind of a long process; to get us there, let’s visit once again our cell castle.

As you may recall, the lord of the castle is the nucleus, the brain of the cell. Today in our castle, the lord has received a letter from his brother telling him of a wonderful new saddle design; the lord decides he must have such a saddle made right away. The letter is like the DNA, while the saddle design is like the gene; the letter has many other things in it besides the design (how Auntie Mable is doing, if the crops are growing well, and so forth), but all that the lord needs right now is the bit about how to make the saddle.

The first thing that the lord will do is call his scribe to come and make a copy of that part of the letter to take to the saddle maker. In the cell, this is going to look like copying the particular gene from the whole of the creature’s DNA, a process known as transcription. An enzyme (a special kind of protein that makes things happen in your body) comes and unzips the double helix, breaking apart the bonded nucleotides and straightening out the ladder. Then, just as the scribe copies the saddle design, another nucleic acid, ribonucleic acid (RNA), copies one side of the DNA. RNA is like DNA except that it has only one strand rather than two, making it look like a ladder that has been cut in half lengthwise. Also, it doesn’t use thymine (T) but instead uses the nucleotide uracil (U) in its place. The messenger RNA (mRNA – the particular type of RNA used here) forms by grabbing nucleotides out of the nucleus (where they are just swimming around waiting to be of assistance) to complement those on the DNA. In the end, the copy is like a mirror image, where the original TCA on the DNA looks like AGU on the mRNA.

So now we have a copy of the gene, but we still don’t have the protein that we need – time for translation! The mRNA leaves the nucleus and goes into the cytoplasm, looking for a ribosome. The ribsosome reads the mRNA to build the protein that the DNA has requested. In our castle, the scribe is hurrying through the bailey, headed for the saddle maker’s workshop. The saddle maker looks over the design and calls for his apprentice to bring him the wood, leather, and nails that he needs to make the design. Shrinking back down to the cell level, you will recall that proteins are made of amino acids (like a medieval saddle is made of wood, leather, and nails). The amino acids are brought to the cell by another type of RNA known as transfer RNA (tRNA). Each cross-shaped tRNA is equipped with three nucleotides which are like a code that goes with a particular amino acid (and they match up with each set of three nucleotides on the mRNA – the ones on the mRNA are called the codon and the ones on the tRNA are called the anticodon). For example a tRNA with a UUC anticodon would always have attached on its other end a lysine amino acid while one with the codon ACC would bring a tryptophan.

The mRNA goes into the ribosome, which reads each codon and the right tRNA bring its amino acid and attaches it to the growing protein chain, like the saddle maker fitting together pieces of wood, carving it into the right shape and finishing the saddle with leather and nails. When the ribosome gets to the end of the mRNA, the protein chain breaks free and folds into its shape. The protein is finally ready to do its job, and the saddle is ready to take its rider. The lord didn’t make it, nor the letter, the scribe, or the apprentice. Even the saddle maker could not have made it on his own – he needed the instructions from the lord. Similarly, without the mRNA, the ribosome, the tRNA, and the protein made from amino acids, the DNA could not make anything happen in the creature. The proteins might stay in the cell or leave depending on its job, but either way it will ensure that the creature looks and works in the way that the Creator intended.