Lesson 07: Energetics of Living Systems

Kinetic energy

The energy of motion.

Potential energy

Stored energy, representing the capacity to move.

Oxidation

The loss of an electron by an atom or molecule, moving it to a lower energy level.

Reduction

The gain of an electron by an atom or molecule, moving it to a higher energy level.

Coupled Reactions

Oxidation and reduction reactions that always occur together.

First Law (Conservation of Energy)

Energy cannot be created or destroyed; it only changes forms.

Second Law (Entropy/Disorder)

The entropy (disorder) of the universe continuously increases as energy transformations spontaneously proceed to convert matter from more ordered/less stable to less ordered/more stable forms.

Gibbs Free Energy

The energy available to do work in a system, calculated as G = H - TS.

Endergonic Reactions

Reactions where the change in free energy (\Delta G) is positive, meaning products have more free energy than reactants and require energy input to proceed spontaneously.

Exergonic Reactions

Reactions where the change in free energy (\Delta G) is negative, meaning products have less free energy than reactants and proceed spontaneously, releasing energy (often as heat).

Activation Energy

The extra energy needed to initiate a chemical reaction by destabilizing existing bonds.

Catalysts

Substances that influence chemical bonds to lower activation energy without being changed or consumed in the reaction, and without altering the proportion of reactant converted to product.

Enzymes as Biological Catalysts

Primarily proteins (and some RNA, ribozymes) that regulate chemical reactions within cells by lowering activation energy.

Active Site

Pockets or clefts on an enzyme where substrates bind, with a precise fit that allows amino acid side chains to interact with and stress substrate bonds, lowering activation energy.

Induced Fit

A phenomenon where substrate binding often induces the enzyme to change its shape, thereby improving the interaction between the enzyme and substrate.

Allosteric Enzymes

Enzymes that exist in active or inactive forms, regulated by molecules binding to an allosteric site.

Enzyme Inhibitors

Molecules that bind to an enzyme and decrease its activity.

Competitive Inhibitors

Enzyme inhibitors that compete with the substrate for binding to the active site.

Non-competitive Inhibitors

Enzyme inhibitors that bind to an allosteric site (a site other than the active site), inducing a shape change that prevents substrate binding.

Allosteric Activators

Regulatory molecules that bind to allosteric sites and activate the enzyme.

Metabolism

The total of all chemical reactions carried out by an organism.

Anabolic (Anabolism)

Metabolic reactions that expend energy to synthesize larger molecules from smaller ones (e.g., amino acids, fatty acids).

Catabolic (Catabolism)

Metabolic reactions that harvest energy by breaking down larger molecules into smaller ones (e.g., carbohydrates, lipids).

Biochemical Pathways

Chemical reactions organized in a sequence where the product of one reaction becomes the substrate for the next.

Feedback Inhibition

A mechanism for controlling biochemical pathways where the end product of a pathway binds to an allosteric site on the enzyme that catalyzes the first reaction, shutting off the pathway.

Adenosine Triphosphate (ATP)

A major form of chemical potential energy and the main energy currency for all cell types.

ATP Structure

A nucleotide consisting of an adenine base, a five-carbon sugar ribose, and a chain of three phosphates, which stores energy in the covalent bonds between the phosphate groups.

ATP Hydrolysis

The breaking of high-energy phosphate bonds in ATP (e.g., ATP o ADP + Pi) to release substantial energy, which drives endergonic reactions.

ATP Cycle

The continuous process where ATP hydrolysis provides energy for endergonic processes, and ATP synthesis depends on energy from exergonic reactions, with ADP and Pi serving as reactants for new ATP synthesis.

Coupled reactions

Reactions that combine exergonic and endergonic reactions for a net negative \Delta G, allowing energy released from one to drive the other.

Phosphorylation

A process where an enzyme called a kinase hydrolyzes ATP and covalently attaches the released phosphate group to a target protein, often acting as a molecular switch to activate or inactivate the protein.

Kinase

An enzyme that hydrolyzes ATP and covalently attaches the released phosphate group to a target protein, often on serine, threonine, or tyrosine side chains.

Dephosphorylation

A process where an enzyme called a phosphatase removes a phosphate group from a protein.

Phosphatase

An enzyme that removes a phosphate group from a protein.