Rise Of The Retrovirals…

I watched Rise of the Planet of the Apes this evening, which had been recommended (and lent) to me by JHB. He is very kind with such things, even though it sometimes takes me several years to return a DVD. I expect most of you have seen it and marvelled at the effects that seamlessly integrate animated apes with live action. I have read some articles criticising how realistic the apes are but I thought it was outstanding. I never once felt that I was watching an animated film. A few thoughts did occur to me though whilst I watched it because I always seem to have my science hat on even when I am submerged in an obvious fantasy.

California seems to have a phenomenal chimpanzee population. The few experimental animals quickly amassed an army, all of whom inherited the intelligence instantly. Caesar took eight years to learn his sign language – the others picked it up during their first interaction. Remarkable! Also the drug’s effect on John Lithgo is literally overnight. In reality, any retroviral drug takes time to work its way through the body.

Viruses are used for gene therapy in a way similar to that described in the film although I doubt that most scientists live in such luxury. A virus is not usually classified as a living thing because it is not able to reproduce without a host organism. I will explain what this means in more detail further down the page. The premise of the film is that retroviruses are being used to add DNA to chimpanzees in the hope of finding a cure for the regressive effects of Alzeimer’s disease. Most families will know somebody at some point who suffers from this terrible condition. It causes loss of memory, changes in personality and problems with communication and reasoning. The scientists in the film were hoping to use DNA introduced through viruses to reverse this effect. The viruses infect the subject then the DNA is added to brain cells and begins to alter the brain’s structure and function.

I said earlier that viruses are not usually classified as being alive. You will know that the standard definition for being alive includes seven specific processes…

• Respiration – the release of energy from glucose, usually involving oxygen
• Excretion – the removal of waste products from the cells of the organism
• Nutrition – the need for absorbing nourishment from the environment, or in the case of plants, for making it themselves
• Growth – single celled organisms grow until they are large enough to divide into two, multicellular organisms replace old and damaged cells in a continuous process
• sensitivity – organisms can sense changes in their environment. This may be simple things like light or sound, or in the case of more complex organisms electrical signals or changes in odour
• Reproduction – living things produce offspring (usually sexually but in some instances they do so asexually)
• Movement – living things are able to move either in the sense that we do or in more subtle ways such as leaves turning to face the sun

Living things are thus grouped into 5 Kingdoms (since Robert Whittaker in 1969), comprising two ’empires’ of the prokaryotes and the eukaryotes. The prokaryotes are single-celled organisms without a nucleus – basically bacteria.

The eukaryotes are more modern organisms that do have a nucleus and are divided into four further kingdoms…

• Protista – single celled animals (protozoa) and simple plants (protophytes) including single-celled algae but also other thallophytes such as sea-weed
• Plants – organisms that make their food by photosynthesis (homotrophic)
• Fungi – such as yeast, mould and mushrooms. Their cell walls contain chitin (rather than the cellulose in plant cell walls). They extract their nutrition from other decaying organisms
• Animals – multi-cellular, mobile organisms that get their nutrition from other living things (heterotrophic)

Viruses don’t quite fit into any of these categories. They infect their host and inject their genetic material into their hosts DNA. The host then makes copies of the virus which exits the cell to infect another cell elsewhere. The retroviruses used in medical research have a simpler RNA molecule to carry their genes rather than the double stranded DNA that you and I share.

Questions…

1. What is a gene?
2. Give an example of a single-celled animal.
3. What are the raw materials for photosynthesis? (I seem to ask this on every post!)
4. Name a chemical that you excrete.
5. What is the Kingdom, Phylum, Class, Order, Family, Genus and Species of a chimpanzee.