: The functional form of a molecule (e.g., a four-unit hemoglobin complex), which may differ from the Asymmetric Unit (the smallest portion used to solve the crystal structure).
: An "Entity" is a unique molecule (like a specific protein chain), while an "Instance" (or Chain ID) is a specific copy of that molecule within the structure (e.g., Chain A and Chain B). 2. Standard File Formats P.D.B.
The is the worldwide repository for the 3D structural data of large biological molecules, such as proteins and nucleic acids. This guide provides the essentials for navigating and understanding its data. 1. Core Concepts & Identifiers : The functional form of a molecule (e