Inorganic and Organic Compounds Essential to Human Functioning

2.4 - Inorganic Compounds Essential to Human Functioning

• Types of Compounds

•     Compounds can be categorized into two broad classes based on their elemental composition and origin:

  • Inorganic Compounds:

    • Definition: Substances that typically do not contain both carbon and hydrogen atoms bonded together. Many inorganic compounds are simple in structure.

    • Common Inorganic Compounds:

      • Water $(\text{H}_2\text{O})$, the most abundant inorganic compound in the body, essential for nearly all physiological processes.

      • Hydrochloric acid $(\text{HCl})$, a strong acid produced by the stomach to aid digestion and kill pathogens.

      • Carbon dioxide $(\text{CO}_2)$, a unique exception that contains carbon but is generally classified as inorganic due to its simple structure and prevalence in non-living systems, and its role as a metabolic waste product.

      • Various salts (e.g., $(\text{NaCl})$, $(\text{KCl})$) and many acids and bases.

  • Organic Compounds:

    • Definition: Substances that contain both carbon and hydrogen, often forming complex molecular backbones. These compounds are large and structurally diverse.

    • Synthesis: Predominantly created through covalent bonds by living organisms, including humans, via metabolic pathways.

    • Significance: Carbon and hydrogen are the second and third most abundant elements in the body, respectively, forming the building blocks of macromolecules that influence various bodily functions and structures, such as energy storage, genetic information, and structural support.

Essential Inorganic Compounds

• The next section details four critical groups of inorganic compounds necessary for life: water, salts, acids, and bases.

Water

• Abundance: Comprises approximately 70% of an adult's body weight, making it the most vital inorganic compound. It serves as the medium for all cellular activities.

• Roles in the Body:

  • Lubricant and Cushion:

    • Major component of lubricating fluids such as synovial fluid in joints (reducing friction), pleural fluid in lungs (facilitating movement), and cerebral spinal fluid (around the brain and spinal cord).

    • Ensures smooth movement of food through the digestive tract via mucus and saliva and protects delicate organs from trauma through its cushioning properties (e.g., amniotic fluid protects a fetus).

  • Heat Sink:

    • Definition: Water has a high specific heat capacity, meaning it can absorb and release large amounts of heat energy without experiencing drastic changes in its own temperature.

    • Mechanism: This property helps maintain a stable internal body temperature (homeostasis). It removes excess heat during high environmental temperatures or strenuous activity through evaporative cooling (sweating) and by distributing heat via blood circulation throughout the body.

  • Component of Liquid Mixtures:

    • Mixture Definition: A combination of substances that are physically blended but retain their individual chemical identities and properties. Water forms the solvent for many biological mixtures.

    • Types of Liquid Mixtures Containing Water:

      • Solutions: Homogeneous mixtures where solutes (the minor component) are uniformly and completely dissolved in a solvent (the major component), forming a clear liquid (e.g., glucose dissolved in blood plasma, sugar in water).

      • Colloids: Heterogeneous or opaque mixtures with larger solute particles that remain dispersed and do not settle out. These particles are large enough to scatter light (Tyndall effect) but too small to be visible individually (e.g., milk, cytoplasm within cells).

      • Suspensions: Heterogeneous mixtures where solute particles are relatively large and will eventually settle out over time if left undisturbed. They are often opaque (e.g., blood where red blood cells can settle, sand in water).

Importance of Water as a Solvent

• Chemical Reactions: Nearly all vital body chemical reactions, including those involved in metabolism and signaling, occur with compounds dissolved in water, providing a necessary medium for molecular interaction.

• Polarity of Water Molecules: Water molecules are polar (one end is slightly negative, the other slightly positive, due to uneven sharing of electrons between oxygen and hydrogen). This polarity allows water to effectively dissolve ionic compounds (like salts) and other polar covalent compounds, which are termed hydrophilic (water-loving) compounds, by forming hydration shells around ions or hydrogen bonds with polar molecules.

• Nonpolar molecules (like fats and oils) are termed hydrophobic (water-fearing) and do not dissolve well in water, tending to aggregate away from water.

Concentrations of Solutes

• Definition: Refers to the precise amount (number of particles or mass) of solute present in a given volume of solution.

• Measurement Units: Concentration is commonly measured in milligrams per deciliter $(\text{mg/dL})$ (often used in clinical settings for substances like glucose) or molarity $(\text{M})$ (moles of solute per liter of solution, preferred for chemical reactions due to its relation to the number of molecules).

• Example of Glucose Concentration: The average glucose level in the blood of healthy adults is approximately $100\ \text{mg/dL}$. Maintaining these specific concentrations is critical for normal physiological function.

• Calculating Molarity: Molarity is calculated using the molecular weight of a compound. For glucose (C₆H₁₂}O₆), its molarity would depend on the mass dissolved in a liter:

  • Carbon: Atomic weight = $12.011\ \text{g}$, Total for 6 carbons = $6 \times 12.011 = 72.066\ \text{g}$.

  • Hydrogen: Atomic weight = $1.008\ \text{g}$, Total for 12 hydrogens = $12 \times 1.008 = 12.096\ \text{g}$.

  • Oxygen: Atomic weight = $16.00\ \text{g}$, Total for 6 oxygens = $6 \times 16.00 = 96.00\ \text{g}$.

  • Total Molecular Weight of Glucose = $180.156\ \text{g/mol}$. One mole of glucose is $180.156\ \text{g}$.

Water and Chemical Reactions

• Water participates directly in many crucial biological reactions:

  • Dehydration Synthesis (Condensation Reaction):

  • Definition: A chemical reaction where two smaller molecules (monomers) are joined together to form a larger molecule (polymer) with the removal of a water molecule. In this process, one reactant releases a hydrogen atom $(\text{H})$ and another releases a hydroxyl group $(\text{OH})$, which combine to form water as a byproduct.

  • Biological Example: The formation of disaccharides from monosaccharides, or the assembly of proteins from amino acids.

  • Hydrolysis (Decomposition Reaction):

  • Definition: The reverse of dehydration synthesis. Water is used to break down a larger compound into smaller units. During hydrolysis, a water molecule is split into a hydrogen atom $(\text{H})$ and a hydroxyl group $(\text{OH})$, which are then added to the cleaved fragments of the original compound, breaking a chemical bond.

  • Biological Example: The digestion of food, where carbohydrates, proteins, and lipids are broken down into their constituent monomers.

  • Reversibility: Both dehydration synthesis and hydrolysis reactions are reversible and fundamental processes in organic chemistry, enabling the constant building up and breaking down of biological molecules.

Salts

• Formation of Salts: Salts are formed through ionic bonding, which occurs when one atom completely transfers one or more electrons to another atom, resulting in the formation of oppositely charged ions that are attracted to each other.

• Definition of Salts: Ionic compounds that dissociate into ions other than hydrogen ions $(\text{H}^+)$, and hydroxyl ions $(\text{OH}^-)$ when dissolved in water. They are essential for many physiological functions.

• $(\text{NaCl})$ Dissociation Example:

  • When sodium chloride $(\text{NaCl})$ dissolves in water, the polar water molecules surround and separate the $(\text{Na}^+)$ (sodium cation) and $(\text{Cl}^-)$ (chloride anion) ions. This process, called dissociation, is influenced by the polar nature of water molecules, which weaken the ionic bonds.

• Electrolytes: The dissociated ions from salts (e.g., $(\text{Na}^+)$, $(\text{K}^+)$, $(\text{Ca}^{2+})$, $(\text{Cl}^-)$, $(\text{HCO}_3^-)$) are called electrolytes because they can conduct electrical currents in solution. These electrical currents are critical for numerous bodily functions, including the transmission of nerve impulses, muscle contraction, and maintaining proper fluid balance.

Acids and Bases

• The balance between acids and bases (pH) is tightly regulated in the body and is crucial for enzyme function and metabolic processes.

  • Acids:

    • Definition: Substances that release hydrogen ions $(\text{H}^+)$ (protons) when dissolved in an aqueous solution, thereby increasing the $(\text{H}^+)$ concentration.

    • Strong vs Weak Acids:

      • Strong acid: An acid that completely or almost completely ionizes (dissociates) in water, releasing all its $(\text{H}^+)$ ions (e.g., hydrochloric acid $(\text{HCl})$ in the stomach).

      • Weak acid: An acid that only partially ionizes in water, meaning it releases only some of its $(\text{H}^+)$ ions (e.g., acetic acid $(\text{CH}<em>3\text{COOH})$, carbonic acid $(\text{H}</em>2\text{CO}_3)$).

  • Bases:

    • Definition: Substances that either release hydroxyl ions $(\text{OH}^-)$ in solution or accept hydrogen ions $(\text{H}^+)$ from a solution, thereby decreasing the $(\text{H}^+)$ concentration.

    • Examples: Sodium hydroxide $(\text{NaOH})$ is a strong base that releases $(\text{OH}^-)$. Bicarbonate ions $(\text{HCO}_3^-)$ are weak bases that accept $(\text{H}^+)$.

  • pH Scale:

    • Indicates the relative acidity or alkalinity (basicity) of a solution, based on the concentration of hydrogen ions $(\text{H}^+)$.

  • Calculated as the negative logarithm of the hydrogen ion concentration: $\text{pH} = -\log_{10}[\text{H}^+]$. A small change in pH represents a large change in $(\text{H}^+)$ concentration.

  • Ranges from 0 (very acidic, high $(\text{H}^+)$ concentration) to 14 (very basic, low $(\text{H}^+)$ concentration), with 7 being neutral (where $[\text{H}^+] = [\text{OH}^-]$). Blood pH is tightly maintained between 7.35 and 7.45.

  • Buffers:

    • Solutions containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that resist significant changes in pH by neutralizing added acids or bases. Buffers absorb excess $(\text{H}^+)$ or $(\text{OH}^-)$.

    • Biological Importance: Buffers like the bicarbonate buffer system in the blood are crucial for maintaining the precise pH range necessary for cellular enzyme activity and overall physiological homeostasis.

2.5 - Organic Compounds Essential to Human Functioning

Chemistry of Carbon

• Carbon Atoms: Carbon is unique among elements, possessing four electrons in its outermost (valence) shell. This electron configuration makes carbon highly versatile and apt for forming four stable covalent bonds with other carbon atoms or with various other elements (e.g., hydrogen, oxygen, nitrogen, sulfur) to achieve a stable octet.

• Carbon Skeletons: This bonding versatility allows carbon to form long, stable chains, branched networks, or cyclical ring structures, known as carbon skeletons. These diverse architectures form the fundamental framework for the vast array of complex organic molecules vital for life.

• Functional Groups: Specific groups of atoms, often containing oxygen, nitrogen, phosphorus, or sulfur, that are consistently found in different organic molecules. These groups attach to the carbon skeleton and are responsible for the compound's characteristic chemical properties and reactivity.

  • Important functional groups include:

  • Hydroxyl $(\text{O—H})$: Pertaining to alcohols, makes molecules polar and soluble. (Involved in dehydration synthesis & Hydrolysis reactions.)

  • Carboxyl $(\text{—COOH})$: Found in organic acids (fatty and amino), can donate $(\text{H}^+)$.

  • Amino $(\text{—NH}_2)$: Found in amino acids, can accept $(\text{H}^+)$, acting as a base.

  • Methyl $(\text{—CH}_3)$: Nonpolar and can influence gene expression when added to DNA.

  • Phosphate $(\text{—PO}_4^{2-})$: Energy-carrying and structural component of nucleic acids and ATP.

Macromolecules

• Macromolecule Definition: Large, complex organic molecules (e.g., carbohydrates, lipids, proteins, nucleic acids) that are formed from smaller, repeating units called monomers.

• Polymers: Most macromolecules are polymers, formed through the process of dehydration synthesis, which links monomer units together with covalent bonds while removing a water molecule. Conversely, these polymers are broken down into their individual monomers via hydrolysis, a reaction that consumes a water molecule.

Carbohydrates

• Definition: Organic molecules composed of carbon, hydrogen, and oxygen atoms, typically with hydrogen and oxygen in a $2:1$ ratio, matching the general formula CH₂O)_n. They are primarily used for energy and structural support.

• Types:

  • Monosaccharides: Simple sugars, the basic monomeric units of carbohydrates, typically containing 3 to 7 carbon atoms. They are readily absorbed and used for immediate energy (e.g., glucose, fructose, galactose).

    • Important Monosaccharides

      • Glucose: The most important monosaccharide, often called \"blood sugar.\" It is the primary and most readily available source of energy for the body's cells, especially neurons and red blood cells. It's a six-carbon sugar (hexose).

      • Fructose: Commonly found in fruits and honey, it is converted into glucose in the liver. It's also a six-carbon sugar (hexose)

      • Galactose: A component of lactose (milk sugar). It is also converted into glucose in the liver. It's another six-carbon sugar (hexose).

      • Deoxyribose: A five-carbon sugar (pentose) that is a crucial structural component of deoxyribonucleic acid (DNA), forming its sugar-phosphate backbone.

      • Ribose: A five-carbon sugar (pentose) that is a key component of ribonucleic acid (RNA) and adenosine triphosphate (ATP), playing vital roles in protein synthesis and energy transfer.

    • Disaccharides: Formed when two monosaccharides are joined by dehydration synthesis. They must be broken down into monosaccharides for absorption.

      • 3 Important disaccharide formed by dehydration synthesis

        • sucrose (table sugar = glucose + fructose),

        • lactose (milk sugar = glucose + galactose),

        • maltose (malt sugar = glucose + glucose))

    Polysaccharides: Long chains (polymers) of many monosaccharide units linked together. They serve as long-term energy storage or structural components.

    • Important Polysaccharides:  

      • Starches:

        • Definition: Complex carbohydrates produced by plants, serving as their primary long-term energy storage.

        • Structure: Composed of many glucose units linked together, forming either linear (amylose) or branched (amylopectin) chains.

        • Biological Role: When consumed by humans, starches are broken down into glucose, which is then absorbed and used for energy.

      • Glycogen:

        • Definition: The primary form of glucose storage in animals, including humans.

        • Structure: Highly branched polymer of glucose units, allowing for rapid release of glucose when energy is needed.

        • Biological Role: Stored mainly in the liver and muscles. Liver glycogen helps maintain blood glucose levels, while muscle glycogen provides readily available energy for muscle contraction.

      • Cellulose:

        • Definition: A major structural component of plant cell walls, providing rigidity and support to plants.

        • Structure: A linear polymer of glucose units linked by specific beta glycosidic bonds.

        • Biological Role: Humans lack the enzymes necessary to break down these beta linkages, making cellulose indigestible. It functions as dietary fiber, promoting digestive health but providing no nutritional energy.

  • Functions of Carbohydrates

    • Major Energy Source: Carbohydrates are the primary and most readily available source of energy for bodily functions, especially vital for neurons (brain cells) and red blood cells.

    • Structural Roles: They can combine with other macromolecules to form essential structures, such as glycoproteins and glycolipids on cell surfaces (important for cell recognition), and are components of nucleic acids (deoxyribose and ribose sugars).

Lipids

• Definition: A diverse group of hydrophobic organic compounds, meaning they are largely nonpolar and insoluble in water. They are primarily made of hydrocarbons (carbon and hydrogen atoms) and contain less oxygen than carbohydrates.

• Triglycerides (Neutral Fats): The most common type of dietary lipid and the primary form of fat storage in the body.

  • Each molecule is composed of a glycerol backbone (consists of 3 carbons) chemically bonded to three fatty acid chains that extend from each of the carbons of the glycerol

  • They form via dehydration synthesis

• Fatty Acids: Long chains of hydrocarbons with a carboxyl group at one end and a methyl group at the opposite end that extend from the each of the 3 carbons of the glycerol .

  • Saturated Fatty Acids: Contain only single covalent bonds between carbon atoms in their hydrocarbon chain. This allows the chains to pack tightly together, making them solid at room temperature (e.g., animal fats).

  • Unsaturated Fatty Acids: Contain one or more double covalent bonds between carbon atoms in their hydrocarbon chain, which introduces kinks in the chain. These kinks prevent tight packing, making them typically liquid at room temperature (e.g., plant oils).

    • Monounsaturated have one double bond; polyunsaturated have multiple.

• Phospholipids: Modified triglycerides where one fatty acid is replaced by a phosphate-containing group. They are amphipathic, possessing a hydrophilic (polar) head and two hydrophobic (nonpolar) fatty acid tails. This characteristic allows them to form the essential lipid bilayer of cellular membranes.

• Sterols: Lipids composed of four interlocking hydrocarbon rings. They are vital for various functions.

  • Cholesterol: The most important sterol in the human body, serving as a precursor for other steroid hormones (e.g., testosterone, estrogen), vitamin D, and bile salts (which aid in fat digestion).

• Prostaglandins: Lipid compounds derived from fatty acids (specifically arachidonic acid). These act as local tissue hormones (paracrines) and are involved in various short-range physiological responses, mediating inflammation, pain, fever, blood clotting, blood pressure regulation, and reproductive processes.

• Functions of Lipids

  • Long-term Energy Storage: Lipids store more than twice the energy per gram compared to carbohydrates.

  • Insulation and Protection: Adipose tissue (fat) provides thermal insulation and cushions vital organs against physical shock.

  • Vitamin Absorption: Essential for absorbing fat-soluble vitamins (A, D, E, K).

  • Cell Membrane Formation: Phospholipids are the fundamental components of all cellular membranes, regulating what enters and leaves cells.

  • Signaling: Steroid hormones act as chemical messengers throughout the body, and prostaglandins function as local signaling molecules.

Proteins

• Definition: Complex organic molecules made of long chains of amino acids linked together by peptide bonds. They are the most versatile macromolecules, performing the vast majority of cellular functions. Peptide bonds are formed between the carboxyl group of one amino acid and the amino group of another through dehydration synthesis.

• Structure of Proteins: The specific three-dimensional shape of a protein is critical for its function. This shape is determined by four levels of structure:

  • Primary Structure: The unique, linear sequence of amino acids in the polypeptide chain, which is precisely determined by the genetic information encoded in DNA. This sequence is crucial as it dictates all subsequent levels of structure and, ultimately, the protein's function. Even a single alteration in this sequence can significantly impact the protein's overall shape and biological activity.

    • 20 different amino acid groups contribute to nearly all of the thousands of different proteins important to human structure and function, each with unique properties that influence the protein's overall shape and activity. The arrangement of these amino acids determines how proteins fold and interact with other molecules.

  • Secondary Structure: Localized, repetitive folding patterns of the polypeptide chain, primarily formed by hydrogen bonds between the backbone atoms (specifically, the carbonyl oxygen of one peptide bond and the amino hydrogen of another, not the R-groups). Common forms include:

    • Alpha-helices: A stable, spiral shape where the polypeptide chain coils, with hydrogen bonds forming between amino acids four positions apart along the chain.

    • Beta-pleated sheets: A zigzag, folded shape where segments of the polypeptide chain lie side-by-side, connected by hydrogen bonds between adjacent strands.

  • Tertiary Structure: The overall, unique three-dimensional shape of a single polypeptide chain, resulting from interactions between the R-groups (side chains) of the amino acids. These diverse interactions contribute to the specific folding and stability

Functions of Proteins

• Proteins are involved in virtually every cellular process and bodily function. Their functions are incredibly diverse:

  • Structural: Provide physical support and framework (e.g., collagen in connective tissue, keratin in skin, hair, and nails, actin and myosin in muscles).

  • Enzymatic Function: Act as biological catalysts (enzymes) that dramatically speed up the rate of biochemical reactions without being consumed in the process. They bind to specific substrates at an active site, lowering the activation energy required for a reaction.

    • Substrate is a reactant in an enzymatic reaction that is specifically targeted by the enzyme, allowing for precise control of metabolic pathways and overall cellular function.

  • Transport: Move substances across cell membranes (e.g., channel proteins, carrier proteins) or through the bloodstream (e.g., hemoglobin transports oxygen).

  • Defense: Form antibodies to fight infections and play roles in immune responses.

  • Regulatory (Hormonal): Some hormones are proteins (e.g., insulin regulates blood glucose).

  • Movement: Contractile proteins (actin and myosin) enable muscle contraction and cellular movement.

  • Buffering, fluid, and electrolyte balance: Proteins can act as buffers due to their ability to bind or release protons $(\text{H}^+)$ in response to changes in pH, helping maintain acid-base homeostasis.

Nucleotides

• Nucleotide Composition: Nucleotides are the monomers of nucleic acids. Each nucleotide is composed of three components:

  • A phosphate group (one or more).

  • A pentose sugar (a five-carbon sugar: deoxyribose in DNA, ribose in RNA).

  • A nitrogenous base: There are five main types, categorized into purines (adenine (A), guanine (G)) and pyrimidines (cytosine (C), thymine (T) in DNA; uracil (U) in RNA).

• Nucleic Acids: Polymers of nucleotides.

  • Deoxyribonucleic Acid (DNA): Primary molecule for genetic information storage. It forms a double helix structure and contains the genetic blueprint for all cellular proteins and functions.

  • Ribonucleic Acid (RNA): Involved in various aspects of protein synthesis, acting as a messenger (mRNA), ribosomal component (rRNA), and transfer agent (tRNA) of genetic information from DNA to proteins.

Adenosine Triphosphate (ATP): A special type of nucleotide consisting of adenine, ribose, and three phosphate groups. It is the primary energy currency of cells. ATP stores energy in its high-energy phosphate bonds, and this energy is released through hydrolysis, converting ATP to ADP (adenosine diphosphate) and an inorganic phosphate group (Pi), fueling most cellular activities.

• Phosphorylation: The process of adding a phosphate group to a molecule, often an organic molecule like ADP, to store energy or to activate/deactivate proteins and enzymes. The energy released

Conclusion

• Understanding the chemistry of both organic and inorganic compounds, their structures, properties, and interactions, is absolutely essential for grasping the foundational principles of human physiology and biochemistry.

• The intricate interactions and reversible reactions involving these critical compounds are fundamental for all life processes, including metabolism, cellular signaling, maintaining structural integrity, and enabling complex biological functions. A disruption in the balance or availability of these compounds can lead to disease and homeostatic imbalances.