Comprehensive Notes on Polar Molecules, pH Regulation, and Macromolecules

Polar vs Nonpolar; Hydrophilic vs Hydrophobic

Polar molecules arise when two nonmetals share electrons unequally, creating partial charges that make the molecule polar. If polar, a molecule tends to be hydrophilic (water-loving).
Nonpolar molecules lack significant charge separation and tend to be hydrophobic (water-avoiding).
When polar substances are placed in water, they tend to dissolve; nonpolar substances (like oil) do not dissolve well in water and may separate.
Example: Salts (e.g., NaCl) are ionic compounds that dissociate in water into ions: ext{NaCl}
ightarrow ext{Na}^+ + ext{Cl}^-
Hydrocarbons (e.g., oil) are nonpolar and do not mix with water.
Elements found in hydrocarbons: Hydrogen and Carbon.
In the context of biology, oil is nonpolar and does not mix with water.

Solutions, Ionization, and pH basics

When salts like NaCl dissolve, they ionize into Na^+ and Cl^- in solution.
In solutions, molecules can form ions; ionization numbers or counts can be discussed in chemistry conversations.
In biology/anatomy, solutions are categorized as:
- Colloids: larger particles suspended, may stay in suspension depending on size and medium.
- Suspensions: particles are large enough to settle out; example given involved a centrifuge separating components like plasma from cells.
pH is a measure of hydrogen ion concentration; pH stands for potential hydrogen.
pH scale: 0 (very acidic) to 14 (very basic), with 7 being neutral.
pH is measured on a log scale; an example provided: a neutral solution has
[ ext{H}^+] = 1 imes 10^{-7} ext{ M} at pH = 7.
Relationship between hydrogen and hydroxide ions:
[ ext{H}^+][ ext{OH}^-] = 1 imes 10^{-14}
\,( ext{at } 25^ ext{o}C)
Also,
ext{pH} = -rac{}{} ext{log}{10}([ ext{H}^+]) ext{pOH} = -rac{}{} ext{log}{10}([ ext{OH}^-])
and ext{pH} + ext{pOH} = 14
Examples of pH values and corresponding [H^+]:
- pH = 3 → [ ext{H}^+] = 1 imes 10^{-3} ext{ M}
- pH = 7 → [ ext{H}^+] = 1 imes 10^{-7} ext{ M}
- pH = 11 → [ ext{H}^+] = 1 imes 10^{-11} ext{ M}

Blood pH, CO2, and buffering systems

Blood pH fluctuates and must be kept within a narrow range (homeostasis) using buffering systems.
Buffering in the blood largely involves buffering hydrogen ions (H^+) and bicarbonate (HCO3^–); kidneys play a major role by exchanging H^+, K^+, and bicarbonate to maintain balance.
Carbon dioxide (CO₂) levels influence blood pH via a bicarbonate buffering system:
- CO₂ reacts with water to form carbonic acid, which dissociates to H^+ and HCO₃⁻. The enzyme carbonic anhydrase speeds this reaction.
- Reaction (simplified):
  ext{CO}2 + ext{H}2 ext{O}
  ightleftharpoons ext{H}2 ext{CO}3
  ightleftharpoons ext{H}^+ + ext{HCO}_3^-
In tissues, CO₂ produced by metabolism increases H^+ (more acidic); bicarbonate leaves red blood cells (RBCs) in exchange for chloride (Cl⁻) to balance charge (chloride shift).
In the lungs, bicarbonate re-enters RBCs and reacts to release CO₂, which is exhaled. This shifts the reaction back toward CO₂ and water, reducing acidity.
If you hyperventilate, you blow off CO₂, decreasing hydrogen ions, and the blood becomes more basic (alkaline).
Breath rate adjustments are driven by CO₂ concentration, not directly by oxygen level.
Summary: CO₂ concentration acts as a driver for blood pH; buffering and respiratory adjustments work together to maintain homeostasis.

Macromolecules: overview of building blocks and properties

Macromolecules are built from monomers via dehydration (condensation) reactions; water is released in polymer formation. The reverse is hydrolysis (add water to break polymers).
- Dehydration synthesis (condensation): monomer + monomer → polymer +
  {
  m H_2O}
- Hydrolysis (hydration): polymer + ${
  m H_2O}$ → monomer + monomer
Synthesis (anabolic) vs. decomposition (catabolic) processes: anabolism builds up macromolecules; catabolism breaks them down.
End groups on macromolecules: carboxyl groups, amine groups, and other functional groups influence polarity and reactivity.

Carbohydrates

Building blocks: monosaccharides (e.g., glucose, fructose).
Major elements: Carbon (C), Hydrogen (H), Oxygen (O).
General composition: Carbohydrates have a H:O ratio of 2:1; empirical formula often written as
ext{(CH}2 ext{O)}n
Carbon-to-oxygen ratio is typically 1:1 per unit in the repeating unit, with hydrogen roughly double that of carbon in terms of total count for simple sugars.
Examples and storage:
- Disaccharides (two monosaccharides) include sucrose (glucose + fructose).
- Polysaccharides store energy: glycogen is a polymer of glucose used to store energy in animals.
Classification of glycogen vs other polysaccharides: glycogen is a storage polysaccharide; starch is another plant storage polymer; cellulose is a structural polysaccharide.

Lipids

General features: primarily composed of carbon, hydrogen, and oxygen; no fixed ratio like carbohydrates.
Fatty tails are long hydrocarbon chains (nonpolar); phosphate-containing heads create phospholipids (polar head, nonpolar tail).
Phospholipids and membranes:
- Phospholipid bilayer forms the cell membrane, with polar heads facing water and nonpolar tails inside, creating a barrier.
- This arrangement makes membranes selectively permeable: small nonpolar molecules pass easily; polar molecules require transport mechanisms.
Cholesterol is a lipid that contributes to membrane structure and fluidity (often depicted in membranes; its role is not as a polymer monomer).
Lipids do not have a single fixed monomer; they exist as molecules like fats, phospholipids, and steroids.

Proteins

Monomer: amino acids (20 naturally occurring).
Elements in proteins: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) — sometimes sulfur (S) in cysteine-containing proteins.
Amino acid structure: central carbon with an amino group, carboxyl group, hydrogen, and an R group (side chain).
R group determines polarity: polar vs nonpolar; determines the protein’s folding and function.
- If the R group is mainly hydrocarbons (C/H), that region tends to be nonpolar.
- If the R group contains amine, hydroxyl, or other electronegative atoms, it tends to be polar.
- Cysteine contains sulfur and can form disulfide bridges.
Protein structure levels (influenced by amino acid sequence):
- Primary structure: amino acid sequence (determines all higher levels).
- Secondary structure: local folding patterns such as alpha helices and beta-pleated sheets, stabilized mainly by hydrogen bonds.
- Tertiary structure: overall 3D shape formed by interactions among R groups (polar/nonpolar, hydrogen bonds, ionic bonds, disulfide bridges, van der Waals interactions).
- Quaternary structure: assembly of multiple polypeptide subunits into a functional protein (e.g., hemoglobin).
Interactions stabilizing structure:
- Hydrogen bonds between polar groups.
- Van der Waals (hydrophobic) interactions between nonpolar regions.
- Ionic bonds between charged side chains.
- Disulfide bridges between cysteine residues.
Protein types:
- Globular proteins: folded, compact shapes (often enzymes, transport proteins).
- Fibrous proteins: elongated, structural roles (e.g., collagen).
Proteins are essential for virtually all body functions; enzymes act as catalysts that accelerate reactions; without them, many biological processes would not occur at meaningful rates.

Enzymes, temperature, and reaction rates

Enzymes lower the activation energy of reactions, acting as biological catalysts.
Reaction rates depend on temperature: increasing temperature initially increases rate, but excessive heat can denature enzymes, reducing rate.
Enzymes are composed of proteins (and sometimes RNA in ribozymes); their activity depends on structure and environment.

Summary of key concepts and relationships

Polar vs nonpolar determines solubility in water; hydrophilic vs hydrophobic behavior shapes interactions in biology (e.g., cell membranes, transport).
pH and buffering regulate cellular and systemic chemistry; the carbonic acid-bicarbonate buffering system maintains blood pH; kidneys and lungs cooperate to maintain homeostasis.
Macromolecules are built from monomers via dehydration synthesis and broken via hydrolysis; their structure (primary to quaternary) determines function.
Carbohydrates: C, H, O; CH_2O repeating unit; energy storage and structure in organisms.
Lipids: hydrophobic components, phospholipid bilayers, membranes, and cholesterol influence fluidity and permeability.
Proteins: amino acids with diverse R groups; folding governed by sequence; structure determines function; interactions stabilize structure; enzymes accelerate reactions.

Quick reference equations and terms

pH and ionization:
- ext{pH} = -rac{}{} ext{log}_{10}([ ext{H}^+])
- ext{pOH} = -rac{}{} ext{log}_{10}([ ext{OH}^-])
- [ ext{H}^+][ ext{OH}^-] = 1 imes 10^{-14}
- ext{pH} + ext{pOH} = 14
Carbonic acid buffering in blood:
- ext{CO}2 + ext{H}2 ext{O}
  ightleftharpoons ext{H}2 ext{CO}3
  ightleftharpoons ext{H}^+ + ext{HCO}_3^-
- Enzyme: carbonic anhydrase speeds the conversion between CO₂ and H₂CO₃.
Dehydration synthesis (condensation):
- Monomer + Monomer → Polymer +
  {
  m H_2O}
Hydrolysis (hydration):
- Polymer +
  {
  m H_2O} → Monomer + Monomer
Basic protein terms:
- Primary structure: amino acid sequence
- Secondary structure: alpha-helix, beta-pleated sheet, hydrogen bonds
- Tertiary structure: 3D folding; hydrophobic/hydrophilic interactions, disulfide bridges, ionic bonds
- Quaternary structure: multiple polypeptides forming a functional unit