TABLE OF CONTENTS A model should be as simple as possible but not simpler.
Albert Einstein
Photosynthesis is the complex series of processes that enable the conversion of solar energy into chemically stored energy. The absorption of light takes place in photosynthetic antennae systems composed of supramolecular arrays of pigments, and is followed by the ultrafast migration of electronic excitation energy through the antenna arrays to reaction centres (RCs), where energy storage occurs by electron transfer across the photosynthetic membrane, as outlined in Chapter 1. This chapter describes the molecular components and structures of light-harvesting systems, and the mechanisms by which energy transfer occurs. The emphasis will mainly be on the antennae systems of oxygen-evolving organisms (higher plants, algae and cyanobacteria), and the antennae of purple and other photosynthetic bacteria will be described only briefly. In recent years, the detailed structures of the light-harvesting systems and reaction centres of several organisms have been determined, some to atomic resolution. This chapter discusses our current understanding of the structural, dynamic and other features that allow efficient light harvesting in photosynthesis.
Before delving into the details of specific light-harvesting systems in photosynthetic organisms, we will first consider the general concept of a photosynthetic unit (PSU). As Fig. 2.1 shows, a PSU consists of an array of light-absorbing chromophores arranged around a reaction centre. The antenna chromophores may be arranged regularly or irregularly...
