Biophotonics_Concepts_to_Applications

An important nucleotide isadenosine triphosphate(ATP). One molecule of ATP
contains three phosphate groups. A large amount of chemical energy is stored in the
phosphate bonds. When ATP is broken down (hydrolyzed) the energy that is
released is used for many metabolic processes. Because of this function, ATP is
considered to be a universal energy currency for metabolism.
Lipidsare non-polymer macromolecules that are all insoluble in water. Simple
lipids include fats, phospholipids (e.g., lecithin), and steroids. Fats provide
long-term energy storage and insulation in humans and animals. Fats are composed
of glycerin and fatty acids. As shown in Fig.1.10, a fatty acid is a long chain of
carbon-hydrogen (CH) bonds, with a carboxyl group (COOH) at one end.
Phospholipids are found mainly in the cell membranes of living systems and are
used for cell-to-cell signaling. Examples of steroids include cholesterol, estrogen,
and testosterone.

1.6.2 Biological Cells

All organisms consist of two structurally different kinds of cells called prokaryotic
cells and eukaryotic cells.Prokaryotic cellshave few internal structures and no true
cell nucleus. These cells are found only in bacteria, with the smallest cells being
0.1– 1 μm in diameter. Most bacteria are 1– 10 μm in diameter.Eukaryotic cellsare
found in all animals, plants, fungi, and protists (one-celled eukaryotic organisms
that are not fungi, plants, or animals). As is shown in Fig.1.11, eukaryotic cells are
typically 10– 100 μm in diameter and have a true nucleus that is surrounded by a
membranous envelope. The nucleus averages 5μm in diameter and contains most

Nitrogen

base

Sugar

molecule

Phosphate

group

P

O

O O

O

OH

Fig. 1.9 Basic nucleotide
monomer for creating nucleic
acids

Carboxyl group Chain of carbon-hydrogen bonds

Fig. 1.10 Example of a lipid
molecular structure

1.6 Structures of Biological Cells and Tissues 17