Energy is the driving force behind all biological processes. From the food we eat to the air we breathe, chemical reactions power our bodies. These reactions involve the transfer and transformation of energy, allowing us to move, think, and live.

Chemical reactions in our bodies are carefully orchestrated processes. They involve breaking down complex molecules for energy, building new structures, and maintaining balance. Understanding these reactions helps us grasp how our bodies function and adapt to changing conditions.

Energy and Chemical Reactions

Kinetic vs potential energy

• Kinetic energy involves the energy of motion possessed by moving objects, particles, atoms, and molecules
• Potential energy represents stored energy that is available for use but not currently being used, including chemical energy stored in bonds between atoms
• Exergonic reactions release energy, often in the form of heat, with products having less potential energy than reactants, are spontaneous and favorable under all conditions (combustion, cell respiration, hydrolysis reactions)
• Endergonic reactions absorb energy from the surroundings, with products having more potential energy than reactants, are non-spontaneous and require an input of energy to proceed (photosynthesis, anabolic reactions, ATP synthesis)
• Chemical equilibrium occurs when the forward and reverse reaction rates are equal, resulting in no net change in reactant and product concentrations

Energy forms for body functions

• Chemical energy involves potential energy stored in chemical bonds, released during exergonic reactions and absorbed during endergonic reactions (ATP, glucose, fats)
• Mechanical energy encompasses the kinetic energy of moving objects or particles, including energy of muscle contraction, blood flow, and joint movement
• Electrical energy represents the kinetic energy of moving charged particles (electrons or ions), essential for nerve impulse transmission, muscle contraction, and heart function
• Thermal energy (heat) refers to the kinetic energy of random motion of atoms and molecules, generated as a byproduct of many metabolic reactions, maintains body temperature and drives chemical reactions

Chemical Reactions in Biological Systems

Types of biological chemical reactions

• Synthesis (anabolic) reactions involve smaller molecules combining to form larger, more complex molecules, require an input of energy (endergonic) (protein synthesis, glycogen synthesis, lipid synthesis)
• Decomposition (catabolic) reactions break down larger molecules into smaller, simpler molecules, release energy (exergonic) (digestion of nutrients, glycogen breakdown, beta-oxidation of fatty acids)
• Exchange reactions involve atoms or functional groups being exchanged between molecules, may be exergonic or endergonic (transamination reactions, phosphorylation reactions)
• Redox reactions involve the transfer of electrons between molecules, playing a crucial role in energy metabolism and cellular respiration

Factors in chemical reaction speed

• Temperature: Higher temperatures increase the kinetic energy of molecules, leading to more frequent collisions and faster reactions; enzymes have optimal temperature ranges; extreme temperatures can denature enzymes
• Concentration of reactants: Higher concentrations of reactants increase the likelihood of collisions, speeding up the reaction rate; applies to enzyme-substrate complexes in biological systems
• Presence of catalysts (enzymes): Lower the activation energy required for a reaction to occur, speed up reactions without being consumed in the process, highly specific to their substrates and reactions
• pH: Changes in pH can alter the structure and function of enzymes; each enzyme has an optimal pH range; deviations can slow down or stop enzyme-catalyzed reactions
• Surface area: Larger surface area of reactants increases the frequency of collisions, speeding up the reaction rate; relevant in digestion, where mechanical and chemical breakdown of food increases surface area for enzymatic reactions

Reaction Kinetics

• Reaction rate refers to the speed at which reactants are converted into products, influenced by factors such as temperature, concentration, and catalysts
• Activation energy is the minimum energy required for a reaction to occur, often lowered by enzymes in biological systems
• The law of mass action states that the rate of a chemical reaction is proportional to the product of the concentrations of the reactants