EVOLUTION INSTALLMENT TWENTY

Chapter Eight (Continued)

RNA5

A very basic molecular machine, necessary to all living beings, is the RNA molecule which, like the DNA molecule, has a backbone consisting of sugar and phosphate molecules, and embedded base pairs. The RNA molecule differs chemically from its DNA kin in two areas: the composition of the sugar molecule and the composition of one base. The deoxyribose5 sugar in the DNA molecule has one less oxygen molecule than the ribose5 molecule in the RNA molecule. As for the base, the hydrocarbon molecule thymine in DNA is replaced in RNA by the different but similar hydrocarbon molecule uracil. The base pairs A-T and T-A in DNA are correspondingly represented by base pairs A-U and U-A in RNA.

RNA also is generally much shorter in length than DNA, and is used for two basic purposes. Messenger RNA {messenger RNA} is used to transcribe sections of DNA code, typically genes, for use within the cell as a template to specify the sequence of amino acids that comprise a specific protein. Transfer RNA {transfer RNA}, on the other hand, is used in conjunction with messenger RNA to actually assemble amino acids in the sequence specified by the messenger RNA. Both messenger and transfer RNA are assisted in this process by a protein machine called a ribosome5 {ribosome}. This machine operates with an intricacy of a sewing machine or a packaging machine on a factory floor to pluck and place, essentially ‘reading’ the information off a segment of messenger RNA to encode a transfer RNA for a specific amino acid molecule, which is picked up by the other end of the transfer RNA and placed onto the growing chain of amino acids comprising the protein being manufactured. After this series of operations, the ribosome advances the RNA to the next section to be ‘read’.

Protein Manufacture6

One function of genes, or sections of DNA representing modular operational subroutines, directs one of the cell’s primary operations, that of manufacturing proteins. Why, one might think, would the cell work so hard to make proteins when they are so readily available as food? Why not just eat what we need, instead of going to the trouble of making our own?

The answer is available only to those of us who are living during the great revolution in microbiological insight taking place before our very eyes, and it’s a fascinating one. The short answer is that proteins are machines, intricate devices like cars or airplanes or forklifts or any number of tools, devices and vehicles that perform useful tasks. Like our bigger machines, they have limited lifetimes. More importantly, they are specialized to perform tasks that are immediately useful only to the cells in which they exist. The proteins in the food we eat aren’t likely to be the proteins that our cells require at that point in time.

Take an old car, for example, and a warehouse that needs a forklift to transport pallets of goods from the storage area to the shipping department. The car would be so inefficient at doing the job of the forklift that the workers using it for that purpose would threaten to quit before the day was out. But there’s a junkyard next door and an ironworks and a forklift factory next to that. It would be much better to take the car to the junky’s, get the metal melted down, sent over to the ironworks and then get it assembled into the forklift that the warehouse needs. Getting the car recycled at the junky’s and the ironworks is akin to the process of digestion in our bodies which recycles unusable proteins into the raw materials that the cell uses to make the protein machinery useful to it.

Proteins are assembled out of the 20 amino acids of left-handed chirality6 that are useful to life among the 80 possible of both chiralities. The amino acids and the sequence in which they are assembled gives them their characteristic shapes and usefulness. This selection of amino acids and the sequence are dictated by the associated gene, or DNA sequence corresponding to that protein. The process works in the following way:

A protein may be thought of as a word. In this context, each of the amino acids that makes up this word can be thought of as a letter. The alphabet of 20 relevant amino acid letters, then, can be represented by a string of 5 binary characters or, equivalently, three base pairs. If the purpose of a gene is to create a specific protein, its DNA is encoded in precisely this manner, where each group of three base pairs represents an associated amino acid.

The sequence of three base pairs encoding for amino acids is preserved in the messenger RNA molecule that represents a copy of that gene. After the DNA-to-RNA copy process is complete, the messenger RNA6 {messenger RNA} enters the ribosome6, which ‘reads’ the sequence from it. At the same time, another type of RNA called transfer RNA {transfer RNA} also enters the ribosome and is placed in proximity to the next available three-base-pair code of the messenger RNA. The other end of this complex-shaped molecule is chemically prepared to accept only the amino acid that corresponds to the code. That amino acid is placed adjacent to the previously attached amino acid chain, called a polypeptide6 chain {polypeptide}. When the chain is complete, a new protein has been formed.

To this point we have described in very simplistic fashion some of the bare essentials of what takes place within living cells. In its investigation of these basic life processes science has encountered some amazingly intricate, machine-like devices and processes such as the hardware and software embedded in the DNA molecule, its replication and division in the mitotic and meiotic cell division processes, messenger and transfer RNA molecules, and protein manufacture.

If the sugar-phosphate backbone and the base-pair ladder rungs of DNA are the essential hardware of a living creature, and if the pattern of embedded base-pairs is the software, then the various combinations of proteins, as directed by switching proteins attached to segments of DNA, are the peripheral equipment associated with life. This peripheral equipment is roughly equivalent to the various computer-driven peripherals like scanners, printers, and Internet modems. However, since all this biological equipment is self-assembling, some equipment is more representative of tools, scaffolding and structural components.

The self-replication and self-assembly of all this complex molecular equipment associated with life adds an additional dimension of complexity on top of the already enormous odds against its mere existence. Moreover, the chicken-egg problem extends down to this level too: the manufacture of proteins within the cell demands the ribosome to convert the RNA codes into amino acid sequences, but the ribosome itself is a complex assembly of interactive proteins that had to exist before it could create itself via the cellular manufacturing process. Yet further, ribosome is useful only in conjunction with RNA. Its existence would be meaningless without it, just as both messenger and transfer RNA molecules would be meaningless of themselves without DNA. Beyond that, each of these very complex mechanisms is, of itself, irreducibly complex in that any subset of it is useless – only the complete mechanism has any use whatsoever. The existence, then, of each enormously complicated component is meaningless not only without its completion, but also without a large number of enormously complicated companion components, all of which are self-replicating and self-assembling. All that’s a lot to ask of a mindless process like evolution. It is, in fact, too much. That’s why the Darwinist can’t afford to think too deeply on this issue.

But, just for the sake of argument, let’s assume for the time being that evolution is capable of such a monumental feat. Then we are forced to confront the even more enormously complicated information embedded in DNA and its own uselessness without all the peripheral equipment required to activate it. But here we’re speaking qualitatively at the level of common sense. In the next chapter we’ll describe how our conclusions can be firmed up with hard numbers.

[to be continued]

NOTES:

5.Meyer, Signature in the Cell, pp. 122-131, Chapter 14; Google on “ribosome”, “ribose sugar”, “deoxyribose sugar”, “messenger RNA”, “transfer RNA”

6.Muncaster, Dismantling Evolution, pp. 124-129; Meyer, Signature in the Cell, pp. 122-131, 206, 207; also Google on “protein manufacture”, “messenger RNA”, “transfer RNA”, “ribosome”, “polypeptide”

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