thermodynamics

Regulation of Enzymes and Metabolic Pathways

• Enzymes can be regulated by allosteric effectors that bind to the allosteric site, altering the shape of the protein to either inhibit or activate enzyme function.
• Metabolic pathways can be regulated at different steps depending on the demands of the cell.
• Negative feedback loops use the product of a pathway to inhibit an enzyme at the beginning of the pathway.

Thermodynamics and Energy Transformations

• The First and Second Laws of Thermodynamics state that energy is transformed in many ways, but always at a cost of energy lost through entropy.
• Free energy (G) is chemical energy available to do work and is expressed as the difference between enthalpy (total energy) and entropy.
• Any reaction involves a change in free energy, ∆G, between reactants and products.
• The direction of change in free energy tells if it is positive or negative ∆G (anabolic or catabolic).

Enzymes and Reaction Coupling

• Enzymes are proteins that reduce the activation energy of a reaction.
• Enzyme specificity and function are the result of the structure (shape) of the protein.
• Substrates interact with enzymes at the active site, forming an enzyme-substrate complex with a close interaction through induced fit.
• Reaction coupling combines a positive ∆G reaction with a negative ∆G reaction to give a new net negative ∆G for the combined reactions.
• The most common means of reaction coupling is to use the hydrolysis of ATP, yielding a ∆G = -7.3 kcal/mole, to generate phosphorylated intermediate molecules of higher energy.

Redox Reactions and Energy Transfer

• Oxidation is the loss of electrons and reduction is the gain of electrons by molecules.
• NADH (or NADPH) is a commonly used high energy electron carrier in metabolism.
• It captures high energy electrons from organic molecules and holds on to them for later when energy from those electrons can be extracted bit by bit using an electron transport chain to do work.

Anabolic and Catabolic Reactions

• Anabolic reactions synthesize or "build" molecules with more bonds, making higher free energy products.
• They use or store energy (endergonic), reduce entropy, and are non-spontaneous.
• Catabolic reactions degrade or "break" molecules to make lower free energy products with fewer bonds.
• They increase entropy and release energy (exergonic), and are spontaneous.

Metabolism and Cellular Processes

• Metabolism is the sum of all anabolic and catabolic reactions in a cell, connected in a network of reaction pathways.
• You should be able to define the first and second laws of thermodynamics and recognize energy transformations and changes in entropy in cellular processes.
• Compare and contrast anabolic and catabolic reactions in terms of change in free energy, change in entropy, if they are spontaneous, and if they are endergonic and exergonic.
• Recognize and explain free energy diagrams for negative and positive delta G reactions.
• Explain the function of enzymes in relation to their structure and their role in negative delta G reactions, and discuss how enzymes are regulated in cells.