Modification of lipid production
In plant cells, genetic manipulation of the mechanism of formation of lipid droplets has staggering implications for seed crops. The biochemistry of production of oils in plant cells follows very similar routes to lipids in animal cells, and one group of enzymes (the diacyl glycerol transferases which catalyse triglyceride production) have already been genetically manipulated to approximately double the yield of oil and oleic acid in maize.
The cytoskeleton
A ‘skeleton’ instantly brings to mind the bony remnants of a long dead individual. The longevity of bone is due to the deposition of minerals such as calcium phosphate into the bone matrix by cells called osteoblasts, creating the structural rigidity. In life, the bones of the human skeleton are held together with tendons and ligaments, flexibly attached to each other as a system of levers, ready to generate movement which is driven by muscle contraction. There are structures with similar functions within cells, where microtubules play the role of levers and the ‘muscle’ activity is provided by actin microfilaments in association with myosin, which slide over each other to provide contraction much as they do in muscle itself. However, unlike the relative rigidity and permanence of our own musculo-skeletal system, the overriding characteristic of the cytoskeleton is one of extreme plasticity and dynamism, where components can be built (polymerized) from building blocks with remarkable speed and just as quickly removed by being broken down (depolymerization). The old-fashioned idea of a cell as essentially a balloon filled with jelly could not be more misleading; cell shape is controlled from within, modulated by signals received from the external environment, and capable of rapid response. Cells continually change their shape, change position relative to their neighbours, move through solid tissues, or take long journeys around the body by entering and exiting the bloodstream. Add to this the reorganization of the entire cytoskeleton required to separate chromosomes at division (as will be described in Chapter 4), and the dynamic nature of the cytoskeleton becomes its main characteristic.