Enzymes, Water, Acids & Bases: Chemical Principles in Anatomy & Physiology

Enzymes, Water, Acids & Bases

Learning Outcomes

• Understand the notation and basic energetics of chemical bond formation.

• Describe the factors that influence reaction rates.

• Explain the properties, actions, and importance of enzymes.

• Discuss the physiologically important properties of water.

• Define and describe the properties of acids and bases with respect to hydrogen ions.

• Explain what the pH scale measures.

• Explain how a pH buffer works.

Chemical Bond Formation & Energetics

Types of Chemical Energy

Chemical reactions in biological systems involve the making and breaking of chemical bonds, which are associated with energy changes.

• Chemical energy: Potential energy stored in chemical bonds.

• Electrical energy: Energy from the flow of ions (e.g., across cell membranes).

• Mechanical energy: Energy directly transferred from one object to another (e.g., muscle contraction).

Endergonic vs. Exergonic Reactions

Chemical reactions can be classified based on their energy requirements or release.

• Endergonic reactions: Require energy input; products have more energy than reactants. Example: Photosynthesis ($6CO_2 + 6H_2O + ext{energy} \rightarrow C_6H_{12}O_6 + 6O_2$).

• Exergonic reactions: Release energy; products have less energy than reactants. Example: Cellular respiration ($C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ext{energy}$).

Reversible reactions can proceed in both directions, depending on conditions (e.g., $CO_2 + H_2O \rightleftharpoons H_2CO_3$).

Factors Influencing Reaction Rates

Key Factors

The rate at which chemical reactions occur in the body is influenced by several factors:

• Physical contact: Reactants must collide.

• Overcoming repulsion: Reactants must overcome repulsive forces.

• Concentration: Higher reactant concentration increases reaction rate.

• Temperature: Higher temperature generally increases reaction rate.

• Catalysts: Substances that speed up reactions without being consumed (e.g., enzymes).

Enzymes: Properties, Actions, and Importance

Definition and Function

Enzymes are biological catalysts that lower the activation energy required for reactions, making them proceed faster and under milder conditions.

• Highly specific: Each enzyme has a unique active site that binds specific substrates.

• Reusable: Enzymes are not consumed in the reaction and can be used repeatedly.

• Regulation: Enzyme activity can be regulated by various factors (see below).

Factors Affecting Enzyme Activity

• Temperature: Increasing temperature speeds up reactions, but high temperatures can denature (unfold) enzymes, reducing activity.

• Substrate concentration: Higher substrate concentration increases reaction rate up to a saturation point.

• Product concentration: High product concentration can slow reaction rate (negative feedback).

• Enzyme concentration: More enzyme increases reaction rate up to a point.

• pH: Enzymes have an optimal pH range; outside this range, their structure and activity are affected. Example: Pepsin (optimal pH ~2, stomach).

Enzyme Deficiencies

Deficiencies in specific enzymes can lead to disease:

• Tay-Sachs Disease: Deficiency of hexosaminidase; accumulation of gangliosides in neurons.

• Severe Combined Immunodeficiency Syndrome (SCIDs): May be due to adenosine deaminase deficiency; results in absence of immune system.

• Phenylketonuria (PKU): Deficiency of phenylalanine hydroxylase; leads to accumulation of phenylalanine, causing neurological damage if untreated.

Physiologically Important Properties of Water

Key Properties

Water is essential for life and has several important physiological properties:

• Heat absorption: Water absorbs heat without significant temperature change.

• Heat transport: Water carries heat when it evaporates (e.g., sweating).

• Cushioning and protection: Water cushions and protects body structures (e.g., cerebrospinal fluid).

• Lubrication: Water acts as a lubricant between adjacent surfaces (e.g., joints).

Water as a Solvent

Water is a universal solvent, able to dissolve many substances:

• Hydrophilic molecules: Dissolve easily in water (charged or polar).

• Hydrophobic molecules: Do not dissolve in water (nonpolar).

• Hydration spheres: Water molecules surround ions, keeping them dissolved and mobile.

Acids, Bases, and Hydrogen Ions

Definitions

• Acids: Electrolytes that dissociate in water, releasing hydrogen ions ($H^+$); proton donors. Example: $HCl \rightarrow H^+ + Cl^-$.

• Bases: Electrolytes that dissociate in water, releasing hydroxide ions ($OH^-$); proton acceptors. Example: $NaOH \rightarrow Na^+ + OH^-$.

The concentration of $H^+$ determines acidity; the concentration of $OH^-$ determines alkalinity.

The pH Scale

Measurement and Meaning

The pH scale measures the concentration of hydrogen ions in solution:

• Formula: $pH = -\log_{10}[H^+]$

• Low pH: High $[H^+]$, acidic solution.

• High pH: Low $[H^+]$, basic (alkaline) solution.

• Neutral pH: $pH = 7$ (pure water).

pH Buffers

Function and Importance

Buffers are molecules that prevent rapid changes in pH by stabilizing hydrogen ion concentration.

• Weak acids and bases: Buffers consist of weak acids and their conjugate bases.

• Mechanism: Buffers release $H^+$ when pH rises and bind $H^+$ when pH falls.

• Example: Carbonic acid-bicarbonate buffer system in blood: $H_2CO_3 \rightleftharpoons HCO_3^- + H^+$

Blood pH Levels

Condition	pH Range
Acidosis	< 7.35
Normal	7.35 - 7.45
Alkalosis	> 7.45

Summary Table: Acids vs. Bases

Property	Acids	Bases
Ion Released	$H^+$	$OH^-$
pH Range	< 7	> 7
Proton Donor/Acceptor	Donor	Acceptor

Example: Hydrochloric acid ($HCl$) is a strong acid; sodium hydroxide ($NaOH$) is a strong base.

Additional info: Some content was inferred and expanded for clarity and completeness, including definitions, examples, and table structure.