CH2 CHEM PT 1 - CHEMICAL BONDING -

Foundations of Chemistry in the Body

• Purpose and approach

  • Introduction to chemistry as the smallest level of organization in physiology.

  • The instructor emphasizes teaching this material as if you haven’t had chemistry before to support everyone, including students with no background.

  • A supportive reminder: even if some students have strong chemistry backgrounds, many peers may find this section challenging.

• Elements and atoms

  • An element is made up of a single kind of atom.

  • Elements in the body have important functions; you should know both the chemical symbol and the general function of key elements.

  • Example discussed: potassium with symbol $K$; function related to normal nervous system function and intracellular roles.

  • Action item: review the lecture notes for a list of essential elements with symbols and functions.

• Ions: charged atoms

  • An ion is an element with a charge.

  • Potassium tends to form a positive ion: $K^+$ (a cation).

  • Reason for positive charge: potassium can lose an electron, becoming more stable overall.

  • Other element example: chlorine tends to form a negative ion: $Cl^-$ (an anion) due to gaining an electron.

  • Distinctions:

  • Cation: positively charged ion (examples: $K^+$, $Na^+$, $Ca^{2+}$).

  • Anion: negatively charged ion (example: $Cl^-$, $HCO_3^-$).

  • Note from instructor: you do not have to determine exact ions for every element, but you should recognize cations vs anions.

  • Memorability mnemonic (personal): a positive person (Kathy) helps recall cation concept.

• Ionic bonding and ionic compounds

  • Ionic bonding involves transfer of electrons from a positively charged ion to a negatively charged ion, creating an ionic bond.

  • Ionic compound: formed when a positively charged ion binds with a negatively charged ion due to opposite charges attracting.

  • Examples:

  • Potassium chloride: $KCl$ (ionic compound)

  • Sodium chloride: $NaCl$ (table salt)

  • Mechanism: one element gives up an electron to another element; charges attract and hold the compound together.

  • More complex ions and salts:

  • Calcium can exist as a $Ca^{2+}$ cation.

  • Phosphate ion: $PO_4^{3-}$ (a polyatomic anion).

  • Calcium phosphate: salt formed between $Ca^{2+}$ and $PO<em>4^{3-}$, often written as a salt like $Ca</em>3(PO<em>4)</em>2$.

  • Bicarbonate ion: $HCO_3^-$ (an anion).

  • Redefining term: salts are often referred to as ionic compounds; widely present in bones (bone contains calcium salts).

• Covalent bonding: sharing electrons

  • Covalent bond definition: two elements share electrons instead of transferring them.

  • Simple example: two oxygen atoms bond to form $O_2$, typically via a double bond where electrons are shared.

  • Another example: water, $H_2O$, with oxygen bonded to two hydrogens; electrons are shared.

  • Types of covalent bonds based on electron sharing:

  • Nonpolar covalent bond: electrons shared equally (e.g., $O=O$; O and O share electrons evenly).

  • Polar covalent bond: electrons shared unequally; one atom (usually more electronegative) pulls electrons closer.

  • Electronegativity concept (explained with a rope metaphor):

  • Oxygen is a strong puller of electrons; hydrogen is less able to pull them.

  • The stronger pull by oxygen causes partial charges: $ext{O has } \boldsymbol{ frac{ ext{partial}}{-}{}} ext{negative} \big( ext{denoted as } \boldsymbol{ frac{ ext{δ^-}}{}}\big)$ and $ext{H has partial positive} \boldsymbol{ frac{ ext{δ^+}}{}}.$

  • Significance: the type of covalent bond determines bond polarity and the overall properties of molecules.

• Like dissolves like: solubility principles

  • Water is a polar covalent compound (polar solvent).

  • Polarity rules of solubility:

  • Polar and ionic substances dissolve in water.

  • Nonpolar covalent substances tend not to dissolve in water.

  • Examples of things that dissolve in water:

  • Salts (ionic compounds) like $NaCl$, $KCl$, etc.

  • Polar covalent substances: sugars (e.g., glucose), polar amino acids, and most proteins.

  • Consequences in blood: dissolution in water allows transport through the bloodstream.

  • Demonstrations mentioned:

  • An Erlenmeyer with salt dissolved in water shows dissolution aiding transport in the bloodstream.

• Dissolving nonpolar substances and transport of fats

  • Nonpolar covalent substances do not dissolve in water (they are fat-soluble).

  • Examples of nonpolar substances: $O_2$, carbon dioxide (CO₂), fats like cholesterol and triglycerides.

  • Why nonpolar substances don’t readily move in water: lack of charge prevents interaction with water molecules.

  • How the body transports nonpolar fats in blood:

  • Fats are wrapped with protein to form lipoproteins (a fat surrounded by protein) so they can dissolve in the bloodstream.

  • Lipoproteins enable fats to travel through aqueous blood by presenting charged/polar surfaces around the fat core.

  • Real-world relevance: cholesterol measurements reflect lipoprotein-associated cholesterol (HDL vs LDL).

  • HDL: high-density lipoprotein (generally considered protective/beneficial).

  • LDL: low-density lipoprotein (carrying more fat; higher levels are not ideal for health).

  • Context: lipid transport explains how fats reach tissues and how cholesterol tests (HDL/LDL) are interpreted clinically.

• Oxygen transport and the role of proteins

  • Oxygen transport in blood is mediated by the protein hemoglobin.

  • Oxygen is nonpolar and does not dissolve well in water; it is carried by hemoglobin rather than dissolving freely in the plasma.

• Carbon dioxide and gas solubility caveat

  • Carbon dioxide (CO₂) is nonpolar and, per the instructor’s explanation, does not dissolve in water as readily as polar substances; the narrative emphasizes nonpolar solubility limitations and the need for buffering/carrier mechanisms in blood. (Note: in biology, CO₂ does dissolve to some extent in water, but it is transported mainly as bicarbonate in blood and bound to hemoglobin; this transcription focuses on the nonpolar/non-dissolution perspective presented here.)

• Cell membranes and transport across membranes

  • Cell membranes are composed largely of fat (lipid bilayer), which is nonpolar.

  • Inside and outside of the cell are water-rich environments; the lipid barrier favors the passage of fat-soluble (nonpolar) substances.

  • Fat-soluble molecules move easily through the membrane without assistance.

  • Polar substances, like sugars, cannot readily cross the lipid bilayer by simple diffusion.

  • To move sugars into cells, the membrane uses proteins (channels/transporters) that provide a polar pathway, enabling facilitated diffusion or active transport.

  • Lipids and protein transport implications:

  • Fat and lipid-soluble vitamins can cross membranes more readily.

  • Sugar and other polar molecules require membrane proteins to gain entry into cells.

  • Relevance to physiology and disease: sugar uptake into cells is central to cellular respiration and energy production; diabetes involves impaired glucose uptake/utilization, illustrating the membrane transport concept.

• Recap of the three main bond categories and solubility rules

  • Ionic bonds: electrons transfer, resulting in cations and anions that attract each other (e.g., $K^+$ with $Cl^-$ to form $KCl$).

  • Covalent bonds: electrons are shared; subdivided into

  • Nonpolar covalent bonds: equal sharing (e.g., $O<em>2$, $CO</em>2$ in certain contexts with linear symmetry).

  • Polar covalent bonds: unequal sharing leading to partial charges (e.g., $H_2O$ with partial $ext{δ^-}$ on O and partial $ext{δ^+}$ on H).

  • Solubility rules:

  • Water dissolves polar and ionic substances (like dissolves like).

  • Nonpolar substances dissolve in nonpolar environments; fats dissolve in nonpolar solvents unless encapsulated (lipoproteins) to allow transport in aqueous solutions.

  • Practical demonstrations mentioned:

  • Salt water in a Styrofoam cup remains contained due to polarity mismatch; water is polar, Styrofoam is nonpolar.

  • Acetone (nonpolar) can dissolve Styrofoam, illustrating nonpolar–nonpolar dissolution.

• Relevance to physiology and future topics

  • The membrane’s fat composition explains selective permeability: fat-soluble substances cross readily; polar substances require transporters.

  • Understanding solubility is foundational for physiology topics like respiration, nutrient transport, and energy production.

  • The discussion foreshadows upcoming chapters on cellular respiration and transport mechanisms, linking chemistry to physiology.

• Quick reference: key terms and formulas

  • Elements and symbols (examples): $K$, $Cl^-$, $Na^+$, $Ca^{2+}$, $HCO<em>3^-$, $PO</em>4^{3-}$

  - Ionic bonds and compounds: $KCl$, $NaCl$,

  phosphate ion: $PO<em>4^{3-}$ calcium phosphate: $Ca</em>3(PO<em>4)</em>2$

  • Covalent bonds: polar vs nonpolar

  • water: $H_2O$ (polar covalent)

  • oxygen molecule: $O_2$ (nonpolar covalent, double bond)

  • Transport and proteins:

  • hemoglobin for oxygen transport

  • lipoproteins: fats with protein around them for aqueous transport; HDL and LDL distinctions

  • Membrane transport concepts:

  • nonpolar (fat-soluble) molecules cross membranes easily

  • polar molecules require membrane proteins for entry

• Ethical/practical implications mentioned

  • Understanding lipid transport and cholesterol levels has direct implications for health and disease prevention (HDL vs LDL management).

  • The link between chemistry principles and real-world medical tests reinforces the importance of foundational chemistry in medical fields.

• Connections to prior lectures and real-world relevance

  • Ties chemistry basics to anatomy and physiology across topics like blood chemistry, digestion, respiration, and cellular transport.

  • Sets the groundwork for understanding how the body handles nutrients, gases, and waste products through chemical interactions and membrane dynamics.

• Hypothetical scenario to illustrate key concepts

  • If you mix salt (ionic compound) in water (polar solvent), the salt dissociates into ions and becomes solvated, enabling distribution through the bloodstream.

  • If you attempt to dissolve oil (nonpolar) in water, it forms droplets; wrapping the oil with proteins (lipoproteins) allows it to travel in blood without forming large droplets that could block vessels.

• Summative takeaway

  • The body relies on three core bonding types (ionic, polar covalent, nonpolar covalent) and the resulting solubility patterns to determine how substances move, dissolve, and are transported in biological systems.

  • A solid grasp of these principles is essential for understanding physiology, particularly blood chemistry, lipid transport, gas exchange, and membrane transport mechanisms.