Other biological examples

Box 3 Optical tweezers have been used to study a wide variety of different biological systems 

The uses of optical tweezers are extending beyond molecular motors they are manifold and exhaustive. 

Optical tweezers have since been used to stretch and even unwind DNA unfold the tertiary structure of proteins pull on DNA processing enzymes like RNA polymerase as it walks along DNA resist the force produced by viral capsid packaging motors and manipulate entire mammalian cells, sperms and sub-cellular organelles and vesicles. The applications are manifold and the future possibilities are great. 

The authors are grateful for financial support provided by the Medical Research Council UK and the UK IRC in Bionanotechnology. 

Greulich, K.O. (1999). Micromanipulation by Light in Biology and Medicine. Birkhauser  

---

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

Besides these features, the formation of a layer due to an interaction of a stratified fluid with light is itself noteworthy. Analogs to this phenomenon can be found in other media. Examples include photochemical reactions in the atmosphere near the Earth s surface, photochemical reactions in the surface water of the ocean and biological activity near the ocean surface. 

The herbicide activity ascribed to the 1,2,4-oxadiazole derivative 67 (60) has prompted the search for other biologically active derivatives. This example was prepared from the corresponding 5-chloromethyl-1,2,4-oxadiazole 63 via conversion to the HHT 65 through the aminomethyl analog 64. Reaction of the HHT 65 with diethyl phosphite under neat conditions produced the desired diethyl ester intermediate 66, which was hydrolyzed to 67. 

The Staudinger reaction [92], a [2 + 2]-cycloaddition of a ketene and a nucleophilic imine, usually proceeds by an initial imine attack on the ketene thus forming a zwitterionic enolate which subsequently cyclizes. This reaction is an expedient route to p-lactams, the core of numerous antibiotics (e.g., penicillins) and other biologically active molecules [93]. In contrast, for Lewis-base catalyzed asymmetric reactions, nonnucleophilic imines are required (to suppress a noncatalyzed background reaction), bearing, for example, an N-Ts [94] or -Boc-substituent [95]. 

Theoretically, any number of solutes can be separated in this manner and the method has been applied, for example, to the separation of fatty acids, amino acids, polypeptides and other biological materials with distribution... 

Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin, were utilized primarily to protect from inflammation. Other biological effects were also found gradually, for example, induction of apoptosis [94, 95], stimulation of immune activity... 

The discovery of pharmaceuticals commences with the scanning of hundreds of compounds, whether with actual materials (irrational approach) or virtual simulations (rational approach). To discover biopharmaceuticals, we have to examine the compounds within us, for example, hormones or other biological response modihers, and determine how they affect the biological processes. In some cases, we study pathogens such as the influenza virus or bacteria to derive the vaccines. In other cases, we copy these biological response modifiers and use them as replacement therapy. 

---