Energy and Chemical Reactions in Cells

Energy, Chemical Reactions, and Cellular Respiration

• All living organisms require energy.
• Energy is needed for various bodily functions, including powering muscles, pumping blood, absorbing nutrients, exchanging respiratory gases, synthesizing new molecules, and establishing cellular ion concentrations.
• Glucose is broken down through metabolic pathways to form ATP, the energy currency of cells.

Energy: States of Energy

• Energy is the capacity to do work, invisible except for its effects on matter.
• Energy exists in two states: potential energy (stored energy, energy of position) and kinetic energy (energy of motion).
• Energy can be converted from one state to another. For example, water at the top of a dam possesses potential energy, which is transformed into kinetic energy as it falls, and this kinetic energy can be harnessed to do work.
• A concentration gradient across a plasma membrane creates potential energy, similar to water at the top of a dam. Sodium ions moving from high concentration to low concentration across the membrane exhibit kinetic energy.

Energy: Forms of Energy

• Chemical energy is a form of potential energy stored in molecules' chemical bonds.
  • It is the most important form of energy in the body.
  • This energy powers movement, molecule synthesis, and establishing concentration gradients.
  • It's released when bonds are broken.
• Triglycerides are used for long-term energy storage in adipose tissue.
• Glycogen stores glucose in liver and muscle tissue.
• ATP is stored in all cells and is produced continuously, used immediately for energy-requiring processes.
• Proteins can be used as a fuel source, though they primarily have other important functions for the body.

Kinetic Energy Forms

• Electric energy is the movement of charged particles; an example is electricity or ions moving across a plasma membrane, like in a neuron.
• Mechanical energy is exhibited by moving objects; an example is muscle contraction during movement.
• Sound energy comes from molecule compression by a vibrating object; for example, sound waves vibrating the eardrum.
• Radiant energy is the energy of electromagnetic waves that vary in wavelength and frequency. Some forms can penetrate the body and have the potential to damage cells for example; UV rays and X-rays. Visible light is detected by retinal cells of the eye.
• Heat is kinetic energy from random motion and typically isn't usable for work within the body. It's measured as temperature.

Energy: Laws of Thermodynamics

• The first law of thermodynamics states energy cannot be created or destroyed; it only changes form.
• The second law of thermodynamics indicates that some energy is lost as heat when energy transformations occur. The amount of usable energy decreases in these transformations. For example, during physical activity, chemical energy in the body is used to produce mechanical energy (movement), but some of that energy is converted to heat, which is not utilized for productive work.

Chemical Reactions: Chemical Equations

• Metabolism is the collective term for all chemical reactions within the body.

• Chemical reactions occur when chemical bonds in existing molecules are broken, creating new chemical bonds and producing changes summarized in a chemical equation.

• Reactants are substances present at the start of a reaction and are written on the left side of an equation.

• Products are the substances created by a reaction and are written on the right side of the equation. For example, A + B → C where, A and B are reactants and C is the product.

• In a balanced chemical equation, the number of elements on each side of the arrow is equal.

Chemical Reactions: Classification of Chemical Reactions

• Categorized by chemical structure changes, energy changes, or reaction reversibility.
  • Catabolism reactions (breakdown reactions) are classified as the collective term for decomposition reactions.
  • Anabolism reactions (synthesis reactions) are the collective term for synthesis of new chemical bonds.
• Exergonic reactions release energy with a net decrease in potential energy during the reaction.
  • An example of an exergonic reaction is the breakdown of glucose.
• Endergonic reactions require energy with a net increase in the potential energy of the products.
  • An example of an endergonic reaction is the synthesis of proteins from amino acids to form new proteins.
• ATP cycling describes the continuous formation and breakdown of ATP.
  • ATP is produced from energy released during exergonic reactions; fuel molecules are oxidized (break down). Energy is temporarily stored within the bonds within the ATP molecule.
  • ATP energy is then used to power other energy needs of the body.
  • The actual amount of ATP in the body at any given time is relatively small, but its continuous formation and breakdown is essential.

Enzymes: Function of Enzymes

• Enzymes are catalysts that speed up chemical reactions in living organisms. 
• Enzymes decrease the activation energy (energy needed to start a reaction).
• Enzymes facilitate reactions that would already occur, increasing the rate of product formation.
• Uncatalyzed reactions are those that occur without enzymes. 
• Catalyzed reactions are those that occur with enzymes present.

Enzymes: Structure and Location

• Most enzymes are globular proteins with unique three-dimensional shapes.
• The active site is a region of the enzyme that accommodates a reactant (called the substrate).
• The active site's specific shape binds to only one specific reacting substrate, forming an enzyme/substrate complex. The enzyme's shape permits only one type of substrate to bind and catalyze only one specific reaction.

Enzymes: Mechanism of Enzyme Action

• Enzyme catalysis involves four steps:
  1. The substrate enters the active site of the enzyme.
  2. The enzyme changes shape slightly to create an induced fit; the shape change increases the strength of the interactions between the enzyme and substrate.
  3. The change in enzyme shape stresses bonds of the substrate(s), allowing bonds of the substrate(s) to be broken or newly formed
  4. The products are released, and the enzyme is free to catalyze more reactions.

Enzymes: Enzymes and Reaction Rates

• Effect of Temperature on Enzyme Function
  • Optimal temperature for human enzymes ranges from 35°C to 40°C.
  • Moderate rises in body temperature increase enzyme activity; a slight rise in body temperature may help speed up the reactions of enzymes so that they can perform their functions more efficiently.
  • Severe increases in temperature can denature proteins (including enzymes) causing them to lose their shape and function.
• Effect of pH on Enzyme Function
  • Most human enzymes function best between pH 6 and 8, the optimal conditions found in the human body. A change in pH can lead to the break down of the proper shape and structural organization of enzymes, which will in turn affect their ability to bind to reactants (substrates).
  • This loss of shape can happen if the pH is too acidic or too basic, and this commonly happens in other environments, such as the stomach's low pH.

Clinical View: Lactose Intolerance

• Lactose intolerance is caused by a deficiency in lactase, the enzyme needed for breaking the lactose bond into glucose and galactose.
• Symptoms of lactose intolerance include abdominal upset.
• Lactose intolerance is treated through the use of lactase enzymes or by avoiding dairy products, which are common sources of lactose.

Explore the crucial roles energy plays in living organisms, including its forms, the processes of cellular respiration, and energy transformations. Understand how glucose breakdown leads to ATP production and the significance of potential and kinetic energy. This quiz focuses on the essential concepts related to energy in biology.