Energy functions and their relationship to molecular conformation
CS/CME/BioE/Biophys/BMI 279 Oct. 1, 2019 Ron Dror Outline
• Energy functions for biomolecular systems – Definition and properties – Molecular mechanics force fields • What does the energy function tell us about biomolecular conformation? – The Boltzmann distribution – Microstates and macrostates – Free energy
How can we associate a particular energy level or state to a given protein conformation?
In simple terms, lower energy states tend to be more common, while higher energy states tend to be less common. Energy functions for biomolecular systems Energy functions for biomolecular systems
Definition and properties Energy function
• A potential energy function U(x) specifies the total potential energy of a system of atoms as a function of all their positions (x) – For a system with n atoms, x is a vector of length 3n (x, y, and z coordinates for every atom) – In the general case, include not only atoms in the protein but also surrounding atoms (e.g., water) Left: energy of system while moving Right: energy of system while moving a single atom along one dimension a single atom along two dimensions ) ) U U Energy( Energy( Position Position Position Highly strained conformations result in higher potential energy, due to a number of energy-costly interactions (see later slides for types of atomic interactions)
When modeling the energy of a protein system, we account for 1) the potential energy for each atom in our protein and 2) the water molecules surrounding the protein - BOTH are important