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2.5  Physical Quantities in Biology

Also, natural selection per se does not explain how “life” began in the first place. It is pos­

sible to construct speculative arguments on the basis, for example, of RNA replicators being

the “primordial seed” of life, which forms the basis of the RNA world hypothesis. RNA is a

single-​stranded nucleic acid unlike the double-​stranded DNA and so can adopt more com­

plex 3D structures, as seen, for example, in the clover leaf shape of tRNA molecules and in

the large complex RNAP, both used in transcribing the genetic code. Also, RNA can form

a version of the genetic code, seen in RNA viruses and in mRNA molecules that are the

translated versions of coding DNA. Thus, RNA potentially is an autocatalyst for its own

replication, with a by-​product resulting in the generation of peptides, which in turn might

ultimately evolve over many generations into complex enzymes, which can catalyze the for­

mation of other types of biological molecules. There is a further question though of how

cell membranes came into being since these are essential components of the basic cellular

unit of life. However, there is emerging evidence that micelles, small, primordial lipid bilayer

vesicles, may also be autocatalytic, that is, the formation of a micelle makes it more likely for

micelles to form further. But a full discussion of this theory and others of creation myths of

even greater speculation are beyond the scope of this book but are discussed by Dawkins and

elsewhere.

2.4.5  “OMICS” REVOLUTION

Modern genetics technology has permitted the efficient sequencing of the full genome

of several organisms. This has enabled the investigation of the structure, function of, and

interactions between whole genomes. This study is genomics. The equivalent investigation

between the functional interactions of all the proteins in an organism is called “proteomics.”

Many modern biophysical techniques are devoted to genomics and proteomics investigations,

which are discussed in the subsequent chapters of this book. There are now also several

other omics investigations. Epigenomics is devoted to investigating the epigenome, which

is the collection of epigenetics factors in a given organism. Metabolomics studies the set of

metabolites within a given organism. Other such fields are lipidomics (the characterization

of all lipids in an organism), similarly transcriptomics (the study of the collected set of all

TFs in an organism), connectomics (study of the neural connections), and several others.

An interesting new omics discipline is mechanomics (Wang et al., 2014); this embodies the

investigation of all mechanical properties in an organism (especially so at the level of cellular

mechanical signal transduction), which crosses into gene regulation effects, more conven­

tionally thought to be in the regime of transcriptomics, since there is now emerging evi­

dence of mechanical changes to the cell being propagated at the level of the local structure of

DNA and affecting whether genes are switched on or off. Arguably, the most general of the

omics fields of study is that called simply “interactomics”; this investigates the interactome,

which is the collection of all interactions within the organism and so can span multiple length

and time scales and the properties of multiple physical parameters and, one could argue,

embodies the collection of all other omics fields.

2.5  PHYSICAL QUANTITIES IN BIOLOGY

Many of the physical quantities in biological systems have characteristic origins and scales.

Also, part of the difference in language between physical scientists and biologists involves the

scientific units in common use for these physical quantities.

2.5.1  FORCE

The forces relevant to biology extend from the high end of tissue supporting the weight of

large organisms; adult blue whales weigh ~200 tons, and so if the whale is diving at terminal

velocity, the frictional force on the surface will match its weight, equivalent to 2 × 10⁶ N. For