Viruses are submicroscopic agents that can reproduce themselves only inside a living cell. Some or other of them have the capacity to infect every kind of life form. Basically, a virus consists of a protective protein coat with genetic information (RNA or DNA) enclosed inside. In that viruses commandeer the life processes of a cell which they have invaded, they tend not to need a lot of genetic information. Mainly their information deals with how to synthesize the protein coat and any associated molecular machines for packaging the genetic material into the protein coat (capsid).
Viruses are quite diverse: some contain RNA for their genetic information, others have DNA. Some exhibit single stranded molecules of genetic information, others have double sided DNA or RNA. No known viruses contain ribosomes, so they cannot manufacture their own proteins apart from the machinery of a host cell. Viruses also cannot generate or store energy in the form of ATP, depending upon the host cell for that as well.
Since viruses are not themselves alive, that is, not able to reproduce on their own, evolutionary scientists are somewhat at a loss to figure out where they came from. Anyway, there are some amazing viruses which, because of their features, cannot be explained by evolution. For example, in recent years some “gigantic” viruses have been discovered. The first observed were the mimivirus inside free-living amoebas. These may contain 2.5 million nucleotides, far larger than many living bacteria. Virus specialists tell us that these viruses display unimaginable genomic complexity! Other large virus include the tupanviruses which are about the size of a bacterium but may include more than 1200 genes. This is far more than some bacteria which may have 500 genes or fewer. Some of these viruses include polymerase proteins for copying genetic material and some tRNAs for protein construction. Moreover, some giant viruses exhibit unique genes not found in any life forms!
We are all only too aware of the devastating effects more common viruses can have on their victims. These particles can infect people, animals, plants and even bacteria. On their protein capsid exterior, viruses need a very specifically shaped protein which is able to connect with a specific protein receptor on a victim’s cell surface. The virus also needs a very specific means of gaining access to the cell once it has attached itself to the surface.
One of the most interesting examples of how a virus can gain access to the inside of a victim cell, is that used by the bacteriophage. These look like miniature spaceships – an icosahedral head with a projecting tail and stabilizing devices like the kick stand of a bicycle. Anyway, the virus settles tail end down onto a suitable bacterial cell and stabilizes itself with the landing gear.
One of the well-studied phage viruses is the T4 phage which infects E. coli among other victims. This virus exhibits a relatively large head with about 170,000 nucleotides inside. After stabilizing itself on the host cell, it punches a hole in the bacterial wall with “exquisite specificity and efficacy.” The action resembles a spring-loaded spear gun. It happens like this: the tail, which connects with the host cell, has 2 concentric tubes where the outer one contracts and the inner one is thrust with great force into the E. coli cell, shooting DNA stored inside the head into the cell.
At 37 degrees it will take only half an hour for a host of new viruses to be released from the E. coli cell. Upon penetration by the virus, the bacterial cell gene expression stops. Synthesis of virus proteins begins in 5 minutes and DNA replication within 10 minutes. Soon new virus particles begin to form and within 30 minutes the cell bursts, releasing about 400 viral particles available to attack other cells.
The wonder of all this is that some living bacteria exhibit a very similar system to the phage weapon allowing these bacteria to attack other bacteria or eukaryotic cells. These bacteria exhibit what is called the T6SS (type 6 secretion system). Armed with the T6SS, the bacterium punches a hole in the victim’s cell wall or plasma membrane, also with great force. Similarities between the two weapon systems have not escaped the notice of biologists. But how did a virus and a bacterium come to exhibit so similar a weapon? An article in Nature declared: “our findings strengthen the existing hypothesis that the T6SS is evolutionarily and functionally related to the bacteriophage.” [Alistair B. Russell et al. 2011. Type VI secretion delivers bacteriolytic effectors to target cells. Nature 475: 343-347. See p. 346.]
Others suggest that the two weapons are “structurally and functionally related,” [M. Basler et al. 2012. Nature 483: 182-186. See p. 182.] that the T6SS and the phage evolved from a common ancestor, [Kudry.. 2015] or that a “unique ancestral protein fold has given rise to a large number of bacteriophage modules as well as to some related components found in cell-wall embedded bacterial nanomachines.” [David Veesler and Christian Cambillau. 2011. A Common Evolutionary Origin for Tailed-Bacteriophage Functional Modules and Bacterial Machineries. Microbiology and Molecular Biology Reviews September pp. 423-433. See p. 424 and p. 431] These authors justify their conclusions by suggesting that “protein sequences diverge faster than their structures. Therefore, in the case of a shared architecture between two or more proteins, one can assume that a common ancestor might be at the origin of such proteins.” [p. 423]. This certainly sounds like fairy tales because it is the gene sequence which determines the protein structure, not the other way around. These scientists fail to explain how the structure can stay the same while the determining sequence changes.
The problems associated with trying to explain the process behind how a virus and a bacterium developed a common weapon design based on a common ancestor or protein are mind boggling. The logical solution to the problem is that both have a common designer.
Viruses are particularly interesting because the design aspect is so clear.
Also, there are good video clips on-line for the Phi29 bacteriophage packing its DNA into its capsid at 60 atmospheres of pressure. How DNA Got into the Bacteriophage (YouTube, 2 min)