Chapter 9 – Emerging Biophysics Techniques  411

electrical resistance in this way could have significantly very high electrical resistances for

wires whose width is of the nanometer length scale, resulting in a highly inefficient gen­

eration of heat. Nonbiophysical methods for tackling this issue include the use of super­

conductive materials whose electrical resistance can be made exceptionally low. Currently,

these are limited in their use at relatively low temperatures (e.g., liquid nitrogen); however,

it is likely that viable room-​temperature superconductive material will be available in the

near future.

Biophysics-​inspired research into this area has included fabricating nanowires from

single DNA molecule templates that are spatially periodically labeled with alternating

electron-​donor and electron-​acceptor probes. These enable electrical conduction through

a series of quantum tunneling processes, rather than by conventional electron drift.

Similarly, using molecular photonics wires that use a DNA molecule containing multiple

FRET acceptor–​donor pairs along its length enables the transfer of optical information

through space via FRET, thus acting as an optical switch at the nanometer length scale

(Heilemann et al., 2004).

In 2012, the estimated average total power consumption of the human world was ~18

TW (1 TW =​ 1 terawatt =​ 10¹² W), equivalent to the output of almost 10,000 Hoover

Dams. The total power production estimated from global photosynthesis is more like

2000 TW, which may indicate a sensible strategy forward to develop methods to harness

the energy transduction properties of natural photosynthetic systems. However, the total

power available to the Earth from the sun is ~200 PW (1 PW =​ 1 petawatt =​ 10¹⁵ W)—​in

this sense, natural photosynthesis is arguably relatively inefficient at only extracting ~1%

of the available solar energy. Solar energy that is not reflected/​scattered away from plant

leaves is mainly transformed to heat as opposed to being locked in high-​energy chemical

bonds in molecules of sugars.

One route being developed to harness this process more controllably is in the modifi­

cation of natural cyanobacteria (photosynthetic bacteria), potentially to develop synthetic

chloroplasts by introducing them into other more complex organisms. These cyanobacteria

contain carboxysomes, which have a protein shell similar in size and shape to the capsid coat

of viruses but contain the enzyme RuBisCo that catalyzes photosynthesis. The application

of these carboxysomes to different organisms has not yet been clearly demonstrated, but

chloroplasts have been imported into foreign mammalian macrophage cells and zebrafish

embryos, to increase their photosynthetic yield (Agapakis et al., 2011).

Modification of bacteria has also been applied in the development of synthetic strains,

which can generate alcohols as fuels, for example, butanol. This method manipulates the

natural fermentation process by adapting the acetyl-​CoA complex that forms an essential

hub between many metabolic pathways, most importantly in the Krebs cycle (see Chapter 2).

The key challenge is that the alcohol is toxic to the cell, so achieving commercially feasible

concentrations is difficult. However, biophysics tools such as fluorescence microscopy and

mass spectrometry can be used to assist in understanding how the molecular homeostasis of

the acetyl-​CoA is achieved and potentially can be manipulated.

9.3.5  ENGINEERING ARTIFICIAL PEPTIDES, PROTEINS, AND LARGER PROTEIN

COMPLEXES

Bioengineering of peptides and proteins can take multiple forms. One is the genetic

manipulation/​modification of existing native proteins starting from their composition

of natural amino acids. Another is the chemical conjugation of native proteins (see

Chapter 7), which in part crosses over into genetic modification. And finally one can also

utilize unnatural amino acids in peptide and protein synthesis to generate truly artificial

products.

Engineering of proteins using genetic modifications typically involves point mutations

of single amino acids to modify their function. Often, the effect is to impair functionality,

for example, to impair a kinase enzyme from its normal ability to catalyze phosphoryl­

ation, but more rarely to increase functionality in some way. The techniques involved