Enzymes, Water, Acids & Bases: Foundations for Anatomy & Physiology

Enzymes, Water, Acids & Bases

Overview

This study guide covers foundational chemical principles essential for understanding biological processes in Anatomy & Physiology. Topics include chemical bond energetics, reaction rates, enzyme function, water properties, acids and bases, the pH scale, and buffering systems.

Chemical Bond Formation & Energetics

Chemical Energy

Chemical energy is the potential energy stored in chemical bonds. It is released or absorbed during chemical reactions, which are central to cellular processes.

• Chemical energy: Stored in the bonds between atoms and molecules.

• Electrical energy: Results from the movement of charged particles (ions).

• Mechanical energy: Directly transferred from one object to another, often seen in muscle contraction.

Endergonic vs. Exergonic Reactions

Chemical reactions can be classified based on their energy requirements and outputs.

• Endergonic reactions: Require energy input; products have more energy than reactants. Example: Photosynthesis in plants.

• Exergonic reactions: Release energy; reactants have more energy than products. Example: Cellular respiration in cells.

Equation for Gibbs Free Energy:

$\Delta G = G_{products} - G_{reactants}$

• If $\Delta G > 0$, the reaction is endergonic (non-spontaneous).

• If $\Delta G < 0$, the reaction is exergonic (spontaneous).

Example: Photosynthesis is an endergonic process powered by sunlight; cellular respiration is exergonic and provides ATP for cellular work.

Chemical Reactions in Cells

Types of Chemical Reactions

• Synthesis: Two or more reactants combine to form a larger product. Example: $A + B \rightarrow AB$

• Decomposition: A compound breaks down into smaller components. Example: $AB \rightarrow A + B$

• Exchange: Parts of reactants are swapped to form new products. Example: $AB + CD \rightarrow AC + BD$

• Reversible reactions: Can proceed in both directions. Example: $CO_2 + H_2O \rightleftharpoons H_2CO_3$

Key Terms:

• Reactants: Substances that enter a reaction.

• Intermediates: Temporary products formed during a reaction.

• Products: Final substances produced by a reaction.

Factors Influencing Reaction Rates

Key Factors

The rate of a chemical reaction is affected by several variables:

• Concentration: Higher reactant concentration increases reaction rate.

• Temperature: Higher temperature generally increases reaction rate, but extreme heat can denature proteins (enzymes).

• Catalysts: Substances that speed up reactions without being consumed; enzymes are biological catalysts.

• Reactant properties: Physical and chemical characteristics of reactants affect how easily they interact.

Example: Enzyme-catalyzed reactions in the body are highly sensitive to temperature and pH.

Enzymes: Properties, Actions, and Importance

Enzyme Function

Enzymes are biological catalysts that lower the activation energy required for chemical reactions, making them proceed faster and more efficiently.

• Highly specific: Each enzyme acts on a particular substrate due to its unique active site.

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

• Lower activation energy: Enzymes make reactions possible at body temperature.

Equation for Enzyme-Catalyzed Reaction:

$E + S \rightarrow ES \rightarrow E + P$

• E: Enzyme

• S: Substrate

• ES: Enzyme-substrate complex

• P: Product

Factors Affecting Enzyme Activity

• Temperature: Increases reaction rate up to a point; high temperatures denature enzymes.

• Substrate concentration: Higher substrate increases rate until saturation.

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

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

• pH: Each enzyme has an optimal pH; extreme pH can denature enzymes.

Example: Pepsin works best in the acidic environment of the stomach (optimal pH ~2).

Enzyme Deficiencies

Deficiencies in specific enzymes can lead to serious health conditions:

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

• Severe Combined Immunodeficiency Syndrome (SCIDs): Often due to adenosine deaminase deficiency; results in a nearly absent immune system.

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

Physiologically Important Properties of Water

Water's Roles in the Body

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

• Heat absorption: Water absorbs heat without significant temperature change, helping regulate body temperature.

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

• Cushioning and protection: Water protects organs and tissues from physical shock.

• Lubrication: Water reduces friction between adjacent surfaces (e.g., joints).

Water as a Solvent

Water dissolves many substances, facilitating chemical reactions and transport in the body.

• Hydrophilic molecules: Dissolve easily in water (ionic and polar compounds).

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

Example: Electrolytes (e.g., Na+, Cl-) dissolve in water, allowing nerve impulse transmission.

Acids, Bases, and Hydrogen Ions

Acids

Acids are substances that release hydrogen ions (H+) in solution, increasing acidity.

• Electrolytes: Acids ionize and dissociate in water.

• Proton donors: Acids donate H+ to the solution.

• Example: $HCl \rightarrow H^+ + Cl^-$

Bases

Bases are substances that accept hydrogen ions or release hydroxide ions (OH-), increasing alkalinity.

• Electrolytes: Bases ionize and dissociate in water.

• Proton acceptors: Bases accept H+ from the solution.

• Release OH-: $NaOH \rightarrow Na^+ + OH^-$

• OH- + H+ \rightarrow H_2O$

pH Scale and Measurement

Understanding pH

The pH scale measures the concentration of hydrogen ions in a solution, indicating its acidity or alkalinity.

• Neutral pH: Pure water has a pH of 7.

• Acidic solutions: pH < 7; higher concentration of H+.

• Basic (alkaline) solutions: pH > 7; lower concentration of H+, higher OH-.

pH Equation:

$pH = -\log_{10}[H^+]$

• Lower pH = higher acidity

• Higher pH = higher alkalinity

Buffers and pH Regulation

How Buffers Work

Buffers are molecules that stabilize pH by either releasing or binding hydrogen ions, preventing rapid changes in pH.

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

• Release H+ when pH rises (to lower pH).

• Bind H+ when pH falls (to raise pH).

Example: Carbonic acid-bicarbonate buffer system in blood:

$H_2CO_3 \rightleftharpoons HCO_3^- + H^+$

• If pH falls: reaction shifts right, releasing H+.

• If pH rises: reaction shifts left, binding H+.

Blood pH Levels

Condition	pH Range
Death (acidosis)	< 6.8
Acidosis	6.8 - 7.35
Normal	7.35 - 7.45
Alkalosis	7.45 - 7.8
Death (alkalosis)	> 7.8

Additional info: The buffer system is crucial for maintaining homeostasis and proper cellular function.

Organic vs. Inorganic Compounds

Classification

• Organic compounds: Contain carbon bonded to hydrogen (e.g., carbohydrates, proteins, lipids, nucleic acids).

• Inorganic compounds: Generally do not contain carbon-hydrogen bonds (e.g., water, acids, bases, salts).

Example: Water ($H_2O$) is an inorganic compound essential for life.

Summary Table: Key Properties

Property	Acids	Bases	Water
Ionization in Water	Release H+	Release OH-	Partial ionization
pH Range	< 7	> 7	7
Role in Body	Digestion, metabolism	Neutralization, pH balance	Solvent, temperature regulation