This chapterfirst describes the concepts and benefits of biophotonics, gives
illustrations of the disciplines where biophotonics techniques are used, and gives
some basic concepts of light-tissue interactions. Further details of light-tissue inter-
actions are given in Chap. 6. In order to understand the various biophotonics concepts
and their application to medical issues, thefinal section of this chapter gives a brief
tutorial of biological cell and molecular structures, cellular and molecular functions,
and the vocabulary used to describe these structures and functions.
1.8 Problems.
1 :1 If a biological tissue sample has a refractive index n = 1.34, show that the
speed of light in this medium is s = 2.24× 108 m/s = 22.4 cm/ns.
1 :2 Show that the photon energies for UV-C light at 190 nm and UV-A light at
315 nm are 6.53 and 3.94 eV, respectively.
1 :3 Collagen is the most abundant protein in humans and animals. It is organized
into long chains of insolublefibers that have great tensile strength. Collagen is
found in tissues such as bone, teeth, cartilage, tendon, ligament, and the
fibrous matrices of skin and blood vessels. (a) Using literature or Web
resources, describe the basic structural unit of collagen, which is a
triple-stranded helical molecule. (b) What are the three principal amino acids
present in collagen?
1 :4 Elastin is a protein consisting of tissuefibers that can stretch to several times
their normal length and then return to their original configuration when the
stretching tension is released. (a) Using Web resources, what are the four basic
amino acids found in elastin? (b) Give at least four organs in the human body
that contain elastin and briefly describe its function in these organs.
1 :5 When ATP is broken down (hydrolyzed) the energy that is released is used for
many metabolic processes. (a) Using Web resources, draw the chemical
structure of the nucleotide ATP to show the triple phosphate group, the sugar
molecule, and the nitrogen base. (b) Describe how ATP releases energy by
producing adenosine diphosphate (ADP) or adenosine monophosphate
(AMP). (c) What happens to these molecules when an orgasm is resting and
does not need energy immediately?
1 :6 For certain biophotonics procedures, an important factor is the ratio of the
surface area of a cell to its volume. Consider two different spherical cells
called Cell #1 and Cell #2. Suppose Cell #1 has a membrane surface area of
1 μm^2 for every microliter (μL) of volume. If the diameter of Cell #2 isfive
times smaller than the diameter of Cell #1, show that the ratio of the surface
area to the volume for Cell #2 is 5μm^2 /μL.
1 :7 Suppose the body of a 70 kg adult human male contains about 44 billion cells.
If the average mass density of humans is about the same as that of water
(1 gm/cm^3 ), show that the average volume of a human cell is about
1.59× 106 μm^3.
1.7 Summary 21