Chapter Two pt. 2

Enzymes, Water, Acids & Bases

Learning Outcomes

• Understand the notation and basic energetics of chemical bonds and reactions.

• 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.

• Describe how a pH buffer works.

Chemical Bonds and Energetics

Basic Notation and Energetics of Chemical Reactions

Chemical reactions in biological systems involve the making and breaking of chemical bonds, which are associated with energy changes. Understanding these energetics is essential for grasping how cells function.

• Reactants: Substances that enter into a chemical reaction.

• Products: Substances formed as a result of the reaction.

• Intermediates: Molecules formed temporarily during the reaction process.

• Endergonic Reaction: Requires 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 Reaction: Releases 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 (e.g., $AB \rightleftharpoons A + B$)

Additional info: Endergonic reactions are typically anabolic (building molecules), while exergonic reactions are catabolic (breaking down molecules).

Factors Influencing Reaction Rates

Key Factors Affecting Chemical Reaction Rates

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

• Concentration: Higher concentrations of reactants increase the likelihood of collisions and reaction rate.

• Temperature: Increasing temperature generally speeds up reactions, but excessive heat can denature proteins (including enzymes).

• Catalysts: Substances that lower the activation energy required for a reaction, increasing the rate without being consumed.

• Reactant Properties: Physical and chemical properties of reactants (e.g., size, charge) affect their ability to interact.

Additional info: Enzymes are biological catalysts that are highly specific for their substrates.

Enzymes

Properties, Actions, and Importance of Enzymes

Enzymes are proteins that act as catalysts in biological reactions, allowing vital processes to occur rapidly and efficiently at body temperature.

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

• Lower Activation Energy: Enzymes reduce the energy required to start a reaction.

• Reusability: Enzymes return to their original form after catalyzing a reaction.

• Enzyme Deficiencies: Can lead to diseases (e.g., Tay-Sachs disease, SCIDs, phenylketonuria).

Factors Affecting Enzyme Activity

• Temperature: Moderate increases speed up reactions; high temperatures denature enzymes.

• pH: Each enzyme has an optimal pH; deviations can reduce activity (e.g., pepsin works best in acidic stomach environment).

• Substrate Concentration: Increasing substrate increases reaction rate up to a saturation point.

• Product Concentration: High product levels can inhibit enzyme activity (negative feedback).

• Enzyme Concentration: More enzyme increases reaction rate up to a limit.

Example: Sucrase catalyzes the hydrolysis of sucrose into glucose and fructose.

Water: Physiological Properties

Importance of Water in the Human Body

Water is essential for life and has several unique properties that support physiological processes.

• High Heat Capacity: Absorbs heat without significant temperature change.

• Heat of Vaporization: Carries heat away when evaporating (e.g., sweating).

• Cushioning and Lubrication: Protects organs and reduces friction between body structures.

• Solvent Properties: Dissolves hydrophilic (polar and ionic) substances, allowing movement and interaction of ions and molecules.

• Hydration Sphere: Water surrounds ions, keeping them dissolved and mobile.

Additional info: Water makes up about 60% of the human body and is vital for chemical reactions, transport, and temperature regulation.

Acids, Bases, and pH

Properties of Acids and Bases

Acids and bases are substances that affect the concentration of hydrogen ions in solution, influencing pH and many physiological processes.

• Acids: Proton donors; release hydrogen ions ($H^+$) in solution. Example: $HCl \rightarrow H^+ + Cl^-$

• Bases: Proton acceptors; release hydroxide ions ($OH^-$) in solution. Example: $NaOH \rightarrow Na^+ + OH^-$

• Electrolytes: Both acids and bases ionize and dissociate in water, conducting electricity.

• Concentration of $H^+$: Determines acidity; higher $H^+$ means lower pH (more acidic).

• Concentration of $OH^-$: Determines alkalinity; higher $OH^-$ means higher pH (more basic).

pH Scale

The pH scale measures the concentration of hydrogen ions in solution, ranging from 0 (most acidic) to 14 (most basic).

• Formula: $pH = -\log_{10}[H^+]$

• Neutral pH: Water has a neutral pH (~7) because it has equal concentrations of $H^+$ and $OH^-$.

• Acidic Solutions: pH < 7; abundance of $H^+$ ions.

• Basic (Alkaline) Solutions: pH > 7; abundance of $OH^-$ ions.

Summary Table: Properties of Acids and Bases

Property	Acids	Bases
Ion Released	$H^+$	$OH^-$
pH Range	0-6.9	7.1-14
Examples	HCl, H2SO4	NaOH, NH3
Reaction with Water	Releases $H^+$	Releases $OH^-$
Common Uses	Cleaning agents, batteries	Soaps, drain cleaners

pH Buffers

How pH Buffers Work

Buffers are molecules that help maintain stable pH in biological systems by neutralizing excess acids or bases.

• Function: Prevent rapid shifts in pH by releasing or binding $H^+$ ions as needed.

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

• Importance: Maintains blood pH within a narrow range (7.35-7.45); deviations can lead to acidosis or alkalosis.

Additional info: Buffers are essential for homeostasis and proper enzyme function.

pH Indicators

Use of pH Indicators

pH indicators are substances that change color depending on the pH of the solution, allowing for easy identification of acidity or alkalinity.

• Examples: Litmus paper, red cabbage juice.

• Application: Used in laboratory and clinical settings to monitor pH changes.