Chapter 2: Biomolecules, Chemical Bonds, and Protein Function in Physiology

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Function and Mechanism of Physiology

Introduction to Physiology

Physiology is the study of how living organisms function, focusing on the mechanisms that underlie biological processes. Understanding the chemical basis of life is essential for explaining physiological phenomena.

Function: Explains the 'why' of physiological processes (e.g., why do cells need energy?).
Mechanism: Explains the 'how' (e.g., how is energy produced and used in cells?).

Miller’s Experiment and the Origin of Biomolecules

Miller-Urey Experiment (1953)

The Miller-Urey experiment demonstrated that organic molecules necessary for life could form under prebiotic Earth conditions.

Setup: Simulated early Earth’s atmosphere (water, methane, ammonia, hydrogen) with electrical sparks to mimic lightning.
Findings: Formation of amino acids and other organic compounds, supporting the hypothesis that life’s building blocks could arise spontaneously.
Significance: Showed that complex molecules can self-assemble and act as catalysts for biochemical reactions.

Essential Elements for Life

Major and Minor Essential Elements

Living organisms require specific elements for structure and function. These are classified as major and minor essential elements.

Major Essential Elements	Minor Essential Elements
H, C, O, N, Na, Mg, K, Ca, P, S, Cl	Li, F, Zn, Mn, Fe, Co, Ni, Cu, Zn, Se, I, Y, Zr, Nb, Mo, Tc, Ru, Rh, La

Key Point: Catalytic active site metals (e.g., Mg2+, Fe2+/3+, Zn2+) are crucial for enzyme function.

Biomolecules: Classes and Functions

Definition and Classification

Biomolecules are organic molecules essential for life, classified into four main groups:

Carbohydrates: Provide energy and structural support.
Lipids: Store energy, form membranes, and act as signaling molecules.
Proteins: Serve as enzymes, structural components, and signaling molecules.
Nucleotides: Form DNA and RNA, store and transfer genetic information.

Building Blocks: Each class has characteristic monomers (e.g., amino acids for proteins, nucleotides for nucleic acids).

Common Functional Groups

Functional groups determine the chemical properties and reactivity of biomolecules.

Functional Group	Shorthand	Bond Structure
Amino	–NH2	–N–H \| H
Carboxyl (acid)	–COOH	O=C–OH
Hydroxyl	–OH	–O–H
Phosphate	–H2PO4	O \| O–P–O \| O

Atoms, Ions, and Isotopes

Key Elements and Atomic Structure

Atoms consist of protons, neutrons, and electrons. The structure of the atom determines its chemical behavior.

Ions: Atoms or molecules with a net electric charge due to loss or gain of electrons.
Cations: Positively charged ions (e.g., Na+, K+).
Anions: Negatively charged ions (e.g., Cl–, HCO3–).
Isotopes: Atoms of the same element with different numbers of neutrons.

Important Ions in the Body

Cations	Anions
Na+ (Sodium)	Cl– (Chloride)
K+ (Potassium)	HCO3– (Bicarbonate)
Ca2+ (Calcium)	HPO42– (Phosphate)
Mg2+ (Magnesium)	SO42– (Sulfate)

Biological Role of Electrons

Four Major Roles

Forming covalent bonds
Participating in ionic bonds
Creating hydrogen bonds
Facilitating Van der Waals interactions

Types of Chemical Bonds

Covalent Bonds

Covalent bonds involve the sharing of electron pairs between atoms.

Polar Covalent Bonds: Electrons are shared unequally (e.g., H2O).
Non-polar Covalent Bonds: Electrons are shared equally (e.g., O2).

Non-covalent Bonds

Ionic Bonds: Transfer of electrons from one atom to another (e.g., NaCl).
Hydrogen Bonds: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).
Van der Waals Forces: Weak, non-specific interactions between molecules.

Non-covalent Interactions

Hydrophilic: Molecules that interact well with water.
Hydrophobic: Molecules that do not interact well with water.
Molecular Shape: Determined by the types of bonds and interactions present.

Solutions and Solubility

Key Definitions

Solute: Substance dissolved in a solution.
Solvent: Substance that dissolves the solute (usually water in biological systems).
Solution: Homogeneous mixture of solute and solvent.
Solubility: The ability of a substance to dissolve in a solvent.

Acids, Bases, and pH

Concepts and Definitions

Acid: A molecule that donates H+ ions to a solution.
Base: A molecule that accepts H+ ions or produces OH– in solution.
pH: A measure of hydrogen ion concentration; calculated as

Major body fluid pH: Blood pH is tightly regulated around 7.4.

Proteins: Structure and Function

Role of Proteins

Proteins are the primary functional molecules in cells, performing a wide range of tasks.

Enzymes (catalysts)
Structural support
Transport
Signaling
Movement
Defense (immune response)
Regulation of gene expression

Protein Interactions

Activation: Turning protein function on.
Inhibition: Turning protein function off.

Ligand Binding and Binding Sites

Ligand: A molecule that binds specifically to a protein.
Binding Site: The region of the protein where the ligand binds.
Properties: Specificity, affinity, competition, and saturation.

q

Equilibrium Constant (Kd): Describes the affinity between protein and ligand.
Dissociation Equation:

Law of Mass Action: The rate of a chemical reaction is proportional to the product of the concentrations of the reactants.

Factors Affecting Protein Binding

Essential for Binding Activity	Modulators and Factors That Affect Binding
Cofactors: Required for ligand binding at binding site	Competitive inhibitor: Competes directly with ligand by binding to active site
Proteolytic activation: Converts inactive to active form by removing part of molecule	Irreversible antagonist: Binds to binding site and cannot be displaced
	Allosteric modulator: Binds to protein away from binding site and changes activity
	Covalent modulator: Binds covalently to protein and changes its activity
	Physical factors: Changes in temperature or pH can denature protein

Summary and Study Tips

Review the structure and function of biomolecules and their functional groups.
Understand the types of chemical bonds and their biological significance.
Be able to define and distinguish acids, bases, and pH.
Know the major and minor essential elements and important ions in the body.
Master the concepts of protein structure, ligand binding, and factors affecting protein activity.

Additional info: For exam preparation, answer the end-of-chapter questions and concept check questions provided in your textbook.