Comprehensive Study Guide: Chemical Organization of Life

Basic Principles of Chemistry and Matter

• Chemistry is defined as the science of the structure and interactions of matter.
• Matter is anything that has mass and occupies space.
• Mass is the quantitative measurement of the amount of matter a substance contains; weight is the variable force exerted on a mass by gravity.
• Matter exists in three physical states:
  • Solid
  • Liquid
  • Gas
• All matter is composed of basic chemical elements that cannot be broken down into simpler substances by ordinary chemical means.

• Major Chemical Elements (constitute approximately $96\%$ of total body mass):

  • Oxygen ($\text{O}$): $65.0\%$ of total body mass. Essential component of water and many organic molecules; required for cellular generation of adenosine triphosphate ($\text{ATP}$).
  • Carbon ($\text{C}$): $18.5\%$ of total body mass. Forms the foundational carbon skeleton chains and ring structures of all organic molecules (carbohydrates, lipids, proteins, nucleic acids).
  • Hydrogen ($\text{H}$): $9.5\%$ of total body mass. Major constituent of water and organic molecules; its ionized form ($\text{H}^+$) determines the acidity of body fluids.
  • Nitrogen ($\text{N}$): $3.2\%$ of total body mass. Structural component of all proteins and nucleic acids ($\text{DNA}$ and $\text{RNA}$).

• Lesser Chemical Elements (constitute approximately $3.6\%$ of total body mass):

  • Calcium ($\text{Ca}$): $1.5\%$ of total body mass. Imparts hardness to bones and teeth; ionized form ($\text{Ca}^{2+}$) is required for blood clotting, hormone secretion, and muscle contraction.
  • Phosphorus ($\text{P}$): $1.0\%$ of total body mass. Constituent of nucleic acids and $\text{ATP}$ balance; essential for structural integrity of bone and teeth.
  • Potassium ($\text{K}$): $0.35\%$ of total body mass. Ionized form ($\text{K}^+$) is the primary intracellular cation; necessary for generating action potentials in excitable cells.
  • Sulfur ($\text{S}$): $0.25\%$ of total body mass. Structural element in essential vitamins and many functional proteins.
  • Sodium ($\text{Na}$): $0.2\%$ of total body mass. Ionized form ($\text{Na}^+$) is the main extracellular cation; maintains fluid balance and generates action potentials.
  • Chlorine ($\text{Cl}$): $0.2\%$ of total body mass. Ionized form ($\text{Cl}^-$) is the main extracellular anion; maintains systemic water balance.
  • Magnesium ($\text{Mg}$): $0.1\%$ of total body mass. Ionized form ($\text{Mg}^{2+}$) serves as an essential cofactor for numerous enzymatic reactions.
  • Iron ($\text{Fe}$): $0.005\%$ of total body mass. Ionized forms ($\text{Fe}^{2+}$ and $\text{Fe}^{3+}$) form functional centers of hemoglobin and specific oxidative enzymes.

• Trace Elements (constitute approximately $0.4\%$ of total body mass):

  • Aluminum ($\text{Al}$), boron ($\text{B}$), chromium ($\text{Cr}$), cobalt ($\text{Co}$), copper ($\text{Cu}$), fluorine ($\text{F}$), iodine ($\text{I}$), manganese ($\text{Mn}$), molybdenum ($\text{Mo}$), selenium ($\text{Se}$), silicon ($\text{Si}$), tin ($\text{Sn}$), vanadium ($\text{V}$), and zinc ($\text{Zn}$).

Atomic Structure and Subatomic Particles

• Chemical elements are built from unique units of matter called atoms, which are the smallest units of matter that retain the distinct chemical properties of an element.

• An atom consists of three primary subatomic particles:

  • Protons ($\text{p}^+$): Positively charged particles located within the atomic nucleus.
  • Neutrons ($\text{n}^0$): Uncharged (neutral) particles located within the atomic nucleus.
  • Electrons ($\text{e}^-$): Negatively charged particles orbiting around the nucleus in specific energy regions.

• Models of Atomic Structure:

  • Electron Cloud Model: Illustrates the probabilistic three-dimensional regions where electrons are most likely to reside.
  • Electron Shell Model: Depicts electrons orbiting the central nucleus within discrete concentric circles (energy levels).

• Atomic Parameters:

  • Atomic Number: The total count of protons contained within the nucleus of an atom.
  • Mass Number: The total sum of protons and neutrons in an atom's nucleus.
  • Isotopes: Atoms of a single element possessing identical atomic numbers (protons) but differing mass numbers due to varied neutron counts.
  • Atomic Mass (Atomic Weight): The weighted average mass of all naturally occurring stable isotopes of an element expressed in daltons.

• Standard Masses of Subatomic Particles:

  • Neutron mass = $1.008\,\text{daltons}$
  • Proton mass = $1.007\,\text{daltons}$
  • Electron mass = $0.0005\,\text{daltons}$

• Specific Atomic Data of Major Biological Elements:
  • Hydrogen ($\text{H}$): Atomic number = $1$; Mass number = $1$ or $2$; Atomic mass = $1.01\,\text{daltons}$.
  • Carbon ($\text{C}$): Atomic number = $6$; Mass number = $12$ or $13$; Atomic mass = $12.01\,\text{daltons}$.
  • Nitrogen ($\text{N}$): Atomic number = $7$; Mass number = $14$ or $15$; Atomic mass = $14.01\,\text{daltons}$.
  • Oxygen ($\text{O}$): Atomic number = $8$; Mass number = $16$, $17$, or $18$; Atomic mass = $16.00\,\text{daltons}$.
  • Sodium ($\text{Na}$): Atomic number = $11$; Mass number = $23$; Atomic mass = $22.99\,\text{daltons}$.
  • Chlorine ($\text{Cl}$): Atomic number = $17$; Mass number = $35$ or $37$; Atomic mass = $35.45\,\text{daltons}$.
  • Potassium ($\text{K}$): Atomic number = $19$; Mass number = $39$, $40$, or $41$; Atomic mass = $39.10\,\text{daltons}$.
  • Iodine ($\text{I}$): Atomic number = $53$; Mass number = $127$; Atomic mass = $126.90\,\text{daltons}$.

Ions, Molecules, Compounds, and Free Radicals

• Ion: An atom or molecule that has gained or lost one or more valence electrons, giving it a net positive or negative charge.
  • Cation: A positively charged ion formed by electron loss.
  • Anion: A negatively charged ion formed by electron gain.
• Major Biological Cations:
  • Hydrogen ion: $\text{H}^+$
  • Sodium ion: $\text{Na}^+$
  • Potassium ion: $\text{K}^+$
  • Ammonium ion: $\text{NH}_4^+$
  • Magnesium ion: $\text{Mg}^{2+}$
  • Calcium ion: $\text{Ca}^{2+}$
  • Iron (II) ion: $\text{Fe}^{2+}$
  • Iron (III) ion: $\text{Fe}^{3+}$
• Major Biological Anions:
  • Fluoride ion: $\text{F}^-$
  • Chloride ion: $\text{Cl}^-$
  • Iodide ion: $\text{I}^-$
  • Hydroxide ion: $\text{OH}^-$
  • Bicarbonate ion: $\text{HCO}_3^-$
  • Oxide ion: $\text{O}^{2-}$
  • Sulfate ion: $\text{SO}_4^{2-}$
  • Phosphate ion: $\text{PO}_4^{3-}$
• Molecule: Two or more atoms held together by shared electrons.
• Compound: A chemical substance containing two or more different elements that can be broken down chemically into those individual constituent elements.
• Free Radical: An electrically charged atom or group of atoms featuring an unpaired electron in its outermost valence shell.

• Free Radicals and Biological Stress:
  • Highly reactive, unstable species that damage tissue by stripping electrons from surrounding cellular structures.
  • Exogenous sources: Ultraviolet rays from sunlight, atmospheric ozone, X-rays, industrial pollution, cigarette smoke.
  • Neutralization: Antioxidants act to safely donate electrons to inactivate oxygen-derived free radicals without turning into reactive species themselves.

Chemical Bonds

• Chemical bonds are forces of attraction that hold atoms together to achieve stability based on electron configurations in their outermost (valence) shells.

• Ionic Bonds:

  • Formed when one atom donates valence electrons to another, establishing strong electrostatic attraction between oppositely charged ions.

• Example: Sodium ($\text{Na}$) possesses $1$ valence electron, which it donates to Chlorine ($\text{Cl}$), which possesses $7$ valence electrons. This yields $\text{Na}^+$ and $\text{Cl}^-$, forming a crystalline lattice of Sodium Chloride ($\text{NaCl}$).

  • Covalent Bonds:

• Formed when two or more atoms share valence electrons rather than transferring them entirely.

• Single Covalent Bond: Sharing of one pair of electrons (e.g., Hydrogen molecule, $\text{H}_2$ represented as $\text{H}-\text{H}$).
• Double Covalent Bond: Sharing of two pairs of electrons (e.g., Oxygen molecule, $\text{O}_2$ represented as $\text{O}=\text{O}$).
• Triple Covalent Bond: Sharing of three pairs of electrons (e.g., Nitrogen molecule, $\text{N}_2$ represented as $\text{N}\equiv\text{N}$).

• Nonpolar Covalent Bond: Equal sharing of electrons between identical or chemically similar atoms (e.g., Methane, $\text{CH}_4$).

• Polar Covalent Bond: Unequal sharing of electrons due to electronegativity differences, producing partial negative charges ($\delta^-$) near electronegative atoms and partial positive charges ($\delta^+$) near electropositive atoms (e.g., Water, $\text{H}_2\text{O}$).

  • Hydrogen Bonds:

• Weak attractive forces that occur between the partial positive charge ($\delta^+$) of a hydrogen atom and partial negative charges ($\delta^-$) of electronegative atoms (like oxygen or nitrogen) on adjacent molecules.

• Physiological Significance of Hydrogen Bonds in Water:
  • Cohesion: The intermolecular attraction causing like liquid particles to stick together.
  • Surface Tension: A measure of the difficulty of stretching or rupturing the surface of a liquid.

Chemical Reactions, Energy, and Catalysts

• Chemical reactions occur when new chemical bonds form or existing chemical bonds break.
  • Reactants: Initial starting substances converted during a reaction.
  • Products: Final resulting substances produced by a reaction.
  • Metabolism: The total sum of all chemical reactions occurring within an organism.

• Forms of Energy:

  • Potential Energy: Stored energy derived from spatial position or physical state.
  • Kinetic Energy: Energy associated with matter in motion.
  • Chemical Energy: A form of potential energy stored within the chemical bonds of molecules.
  • Law of Conservation of Energy: Energy cannot be created or destroyed, but it can be transformed from one form into another.

• Energy Dynamics in Reactions:

  • Exergonic Reaction: Releases more energy than it absorbs, yielding products with lower potential energy than reactants.
  • Endergonic Reaction: Absorbs more energy than it releases, requiring net energy input.

• Activation Energy: The initial collision energy investment required to destabilizing existing bonds and initiate a chemical reaction.

• Catalysts:
  • Chemical compounds that accelerate chemical reaction rates by reducing the activation energy required.
  • Catalysts orient colliding molecules efficiently and remain structurally unchanged at the conclusion of reactions.

Types of Chemical Reactions

• Synthesis Reactions (Anabolism):
  • Occur when two or more atoms, ions, or molecules combine to form larger, more complex products.
  • Formula: $A + B \rightarrow AB$

• Example: Synthesis of water: $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$.

  • Decomposition Reactions (Catabolism):

• Occur when large complex molecules are split into smaller atoms, ions, or simpler molecules.

• Formula: $AB \rightarrow A + B$

• Example: Decomposition of methane: $\text{CH}_4 \rightarrow \text{C} + 2\text{H}_2$

  • Exchange Reactions:

• Consist of both decomposition and synthesis steps, exchanging structural components between reactant pairs.

• Formula: $AB + CD \rightarrow AD + BC$

• Example: $\text{HCl} + \text{NaHCO}_3 \rightarrow \text{H}_2\text{CO}_3 + \text{NaCl}$

  • Reversible Reactions:

• Can proceed in either direction based on environmental parameters such as reactant concentration or thermal energy.

• Formula: $AB \rightleftharpoons A + B$

• Oxidation-Reduction (Redox) Reactions:
  • Coupled reactions involving electron transfer between molecules.
  • Oxidation: The loss of electrons resulting in a release of stored chemical energy.
  • Reduction: The gain of electrons resulting in a gain of stored chemical energy.
  • Redox processes occur in parallel: when one substance undergoes oxidation, the accepting partner simultaneously undergoes reduction.

Inorganic Compounds, Solutions, and Water

• Inorganic vs. Organic Compounds:

  • Inorganic Compounds: Structurally simple molecules that usually lack carbon chains (e.g., Water, $\text{H}_2\text{O}$).
  • Organic Compounds: Complex chemical structures that always contain carbon and hydrogen, relying heavily on covalent bonds.

• Water as a Biological Solvent:

  • Water is the most abundant inorganic compound in living organisms.

• Dissolution Mechanism: Water's polar structure surrounds charged ions to create hydration shells ($\text{Na}^+$ ions interact with partial negative oxygen atoms $\delta^-$; $\text{Cl}^-$ ions interact with partial positive hydrogen atoms $\delta^+$).

  • Water in Chemical Reactions:

• Hydrolysis Reaction: Breakdown of complex molecules via the addition of a water molecule.

• Dehydration Synthesis Reaction: Joining of two simpler molecules into a complex structure accompanied by the elimination of a water molecule.

  • Thermal Properties of Water:

• High Heat Capacity: Can absorb or release large amounts of thermal energy with minimal changes in its own internal temperature.

• High Heat of Vaporization: Requires substantial energy inputs to convert liquid water into a gaseous state, enabling evaporative cooling.

  • Water as a Lubricant:

• Major component of serous and synovial fluids, reducing frictional resistance between sliding tissue layers and visceral organs.

  • Biological Mixtures:

• A mixture is a physical combination of elements or compounds that blend without forming chemical bonds.

• Three Primary Types:

  • Solution: Homogeneous mixture where solute particles remain dissolved indefinitely.

  • Colloid: Heterogeneous mixture containing larger solute particles that disperse light and do not settle out.

  • Suspension: Heterogeneous mixture with large solute particles that eventually settle out under gravity.

  • Expressing Solution Concentrations:

• Percentage (Mass per Volume): Defined as grams of solute per $100\,\text{mL}$ of solution.

  • Example: A $10\%$ $\text{NaCl}$ solution contains $10\,\text{g}$ of $\text{NaCl}$ dissolved in sufficient water to produce $100\,\text{mL}$ of total solution.

• Molarity (Moles per Liter, $\text{M}$):

  • A $1\,\text{molar}$ ($1\,\text{M}$) solution equals $1\,\text{mole}$ of solute dissolved per $1\,\text{liter}$ of solution.
  • Example: A $1\,\text{M}$ $\text{NaCl}$ solution contains $1\,\text{mole}$ of $\text{NaCl}$ ($58.44\,\text{g}$) dissolved in sufficient water to produce $1\,\text{liter}$ total volume.

Acids, Bases, Salts, pH, and Buffers

• Dissociation Behaviors in Aqueous Solution:

• Acid: Dissociates into hydrogen ions ($\text{H}^+$) and an anion (e.g., $\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$).

• Base: Dissociates into hydroxide ions ($\text{OH}^-$) and a cation, or acts to bind free $\text{H}^+$ (e.g., $\text{KOH} \rightarrow \text{K}^+ + \text{OH}^-$).

• Salt: Dissociates into cations and anions in water, neither of which is $\text{H}^+$ or $\text{OH}^-$ (e.g., $\text{KCl} \rightarrow \text{K}^+ + \text{Cl}^-$).

  • The pH Scale:

• Measures the logarithmic concentration of hydrogen ions ($[\text{H}^+]$) and hydroxide ions ($[\text{OH}^-]$) in $\text{moles/liter}$.

• Acidic Solution: $\text{pH} < 7$ where $[\text{H}^+] > [\text{OH}^-]$.

• Neutral Solution: $\text{pH} = 7$ where $[\text{H}^+] = [\text{OH}^-]$.

• Basic (Alkaline) Solution: $\text{pH} > 7$ where $[\text{H}^+] < [\text{OH}^-]$.

  • Specific pH Values of Human Body Fluids and Common Substances:

• Gastric Juice: $1.2 - 3.0$

• Lemon Juice: $2.3$

• Vinegar: $3.0$

• Carbonated Soft Drink: $3.0 - 3.5$

• Vaginal Fluid: $3.4 - 4.5$

• Orange Juice: $3.5$

• Tomato Juice: $4.2$

• Coffee: $5.0$

• Urine: $4.6 - 8.0$

• Saliva: $6.35 - 6.85$

• Milk: $6.8$

• Distilled (Pure) Water: $7.0$

• Blood: $7.35 - 7.45$

• Semen: $7.20 - 7.60$

• Cerebrospinal Fluid (CSF): $7.4$

• Pancreatic Juice: $7.1 - 8.2$

• Bile: $7.6 - 8.6$

• Milk of Magnesia: $10.5$

• Lye ($\text{Sodium Hydroxide}$): $14.0$

  • Buffer Systems:

• Maintain internal homeostasis by converting strong acids or bases into weak acids or bases.

• Bicarbonate Buffer Equation: $\text{H}^+ + \text{HCO}_3^- \rightleftharpoons \text{H}_2\text{CO}_3$
  • Free hydrogen ions ($\text{H}^+$) combine with bicarbonate ion ($\text{HCO}_3^-$) to form carbonic acid ($\text{H}_2\text{CO}_3$), dampening acidity changes.

Organic Compounds and Functional Groups

• Carbon Properties:

  • Possesses $4$ valence electrons, allowing it to bond with up to four other atoms simultaneously.
  • Forms linear chains, branched chains, and ring backbones.
  • Carbon compounds do not dissolve easily in water, making them ideal structural components.
  • Carbon-carbon covalent bonds store abundant usable chemical energy.

• Major Functional Groups of Organic Molecules:

• Hydroxyl Group ($\text{R}-\text{O}-\text{H}$): Polar and hydrophilic due to electronegative oxygen. Characterizes alcohols.
• Sulfhydryl Group ($\text{R}-\text{S}-\text{H}$): Polar and hydrophilic. Found in thiols (e.g., cysteine) and stabilizes protein shape through disulfide bridges.
• Carbonyl Group ($\text{R}-\text{CO}-\text{R}$ or $\text{R}-\text{CO}-\text{H}$): Polar and hydrophilic. Present in ketones (internal chain placement) and aldehydes (terminal chain placement).

• Carboxyl Group ($\text{R}-\text{COOH}$ or $\text{R}-\text{COO}^-$): Found in carboxylic acids and all amino acids; predominant negatively charged form at body pH is hydrophilic.
• Ester Group ($\text{R}-\text{COO}-\text{R}$): Predominates in dietary fats, oils, and body triglycerides. Present in aspirin (ester of salicylic acid).

• Phosphate Group ($\text{R}-\text{O}-\text{PO}_4^{2-}$): Extremely hydrophilic due to dual negative charges. Key functional unit of $\text{ATP}$.
• Amino Group ($\text{R}-\text{NH}_2$ or $\text{R}-\text{NH}_3^+$): Acts as a base by binding hydrogen ions; present at one end of all amino acids.

Carbohydrates

• Composed of carbon, hydrogen, and oxygen with a ratio of hydrogen to oxygen usually equal to $2:1$ ($\text{C}_n\text{H}_{2n}\text{O}_n$).
• Represents $2 - 3\%$ of total body mass, serving as the primary source of cellular energy.

• Monosaccharides (Simple sugars containing $3$ to $7$ carbon atoms):

• Pentoses ($5$ carbons):

  • Deoxyribose (structural sugar in $\text{DNA}$)
  • Ribose (structural sugar in $\text{RNA}$)

• Hexoses ($6$ carbons):

  • Glucose (main circulating blood sugar)

  • Fructose (found in fruits)

  • Galactose (constituent of milk sugar)

  • Disaccharides (Formed by joining two monosaccharides via dehydration synthesis):

• Sucrose (table sugar) = Glucose + Fructose

• Lactose (milk sugar) = Glucose + Galactose

• Maltose = Glucose + Glucose

  • Polysaccharides (Complex chains composed of tens to hundreds of monosaccharides):

• Glycogen: Highly branched storage carbohydrate in animal liver and skeletal muscle.
• Starch: Primary storage carbohydrate in plants and main source of dietary carbohydrates.
• Cellulose: Structural fiber in plant cell walls that cannot be digested by human enzymes, assisting gastrointestinal transit.

Lipids

• Composed of carbon, hydrogen, and oxygen; possess a low ratio of oxygen to carbon, making them hydrophobic and insoluble in water.

• Functional Categories of Biological Lipids:

  • Fatty Acids: Synthesize triglycerides and phospholipids or undergo catabolism to yield $\text{ATP}$.
  • Saturated Fatty Acids: Contain only single covalent carbon bonds, producing straight hydrocarbon chains.
  • Unsaturated Fatty Acids: Contain one or more double covalent carbon bonds, creating structural kinks (e.g., monounsaturated oleic acid vs. saturated palmitic acid).

• Triglycerides (Fats and Oils):

- Composed of a single glycerol molecule attached to three fatty acid chains through ester linkages via dehydration synthesis.
- Functions: Thermal insulation, organ protection, long-term energy storage.

• Phospholipids:

- Amphipathic molecules containing a charged, polar phosphate head (hydrophilic) and two uncharged nonpolar fatty acid tails (hydrophobic).
- Form the structural lipid bilayer of all cellular membranes.

• Steroids (Molecules built from four fused carbon rings):

- Cholesterol: Minor structural component of animal cell membranes; precursor to bile salts, vitamin D, and steroid hormones.
- Bile Salts: Needed for emulsification and absorption of dietary lipids.
- Vitamin D: Regulates calcium homeostasis, supporting bone growth and repair.
- Adrenocortical Hormones (e.g., Cortisol): Regulate metabolism, stress adaptation, and electrolyte balance.
- Sex Hormones (e.g., Estradiol, Testosterone): Stimulate reproductive physiological functions and secondary sexual traits.

• Eicosanoids:

  • Prostaglandins and Leukotrienes: Derived from 20-carbon fatty acids; modify cellular responses to hormones, blood clotting, inflammation, immunity, stomach acid secretion, airway diameter, and smooth muscle activity.

• Other Lipids:

  • Carotenes: Pigment precursors to Vitamin A used in visual pigment synthesis; act as antioxidants.
  • Vitamin E: Promotes tissue repair, reduces scarring, supports nervous function, acts as an antioxidant.
  • Vitamin K: Required for hepatic synthesis of blood-clotting proteins.
  • Lipoproteins: Water-soluble lipid-protein complexes that transport triglycerides and cholesterol through blood.

Proteins and Enzymes

• Structural and Functional Roles of Proteins:

  • Structural: Form supporting frameworks (e.g., collagen in bone and connective tissues; keratin in skin, hair, and nails).
  • Regulatory: Act as peptide hormones and neurotransmitters (e.g., insulin regulating blood glucose; substance P mediating pain perception).
  • Contractile: Facilitate muscle fiber shortening and physical movement (e.g., myosin and actin).
  • Immunological: Protect against foreign substances and pathogens (e.g., antibodies and interleukins).
  • Transport: Carry vital substances throughout body fluids (e.g., hemoglobin carrying oxygen and carbon dioxide).
  • Catalytic: Act as biological enzymes regulating metabolic reaction rates (e.g., salivary amylase, sucrase, $\text{ATPase}$).

• Amino Acid Building Blocks:

• Proteins are polymers constructed from amino acid monomers.

• Each amino acid contains a central alpha carbon attached to:

  • An amino group ($-\text{NH}_2$
  • A carboxyl group ($-\text{COOH}$
  • A hydrogen atom ($-\text{H}$
  • A variable side chain ($\text{R}$ group) determining chemical behavior.

• Representative Amino Acids: Glycine ($\text{R}=\text{H}$), Cysteine ($\text{R}=\text{CH}_2\text{SH}$), Tyrosine, Lysine.

  • Peptide Bond Formation:

• Covalent peptide bonds form between the carboxyl carbon of one amino acid and the amino nitrogen of another via dehydration synthesis.

• Hydrolysis reactions break peptide bonds by inserting a water molecule.

  • Four Levels of Protein Structural Organization:

• Primary Structure: The linear sequence of amino acids linked together by covalent peptide bonds.

• Secondary Structure: Localized twisting and folding of the polypeptide chain into $\alpha$--helices and $\beta$--pleated sheets, stabilized by hydrogen bonds.

• Tertiary Structure: The three-dimensional folding pattern of a single polypeptide chain held by disulfide bridges, ionic interactions, and hydrophobic effects.

• Quaternary Structure: The spatial arrangement and association of two or more individual polypeptide chains (subunits).

  • Enzymes and Enzymatic Action:

• Enzymes are biological catalysts characterized by high specificity, extreme catalytic efficiency, and tight cellular control.

• Enzymatic Catalysis Mechanism:
  1. Substrate molecules encounter the specific active site on the enzyme surface to form an enzyme-substrate complex.
  2. The enzyme catalyzes the chemical transformation, converting the substrate into final products.
  3. Products detach from the unchanged active site, freeing the enzyme to repeat the process.

Nucleic Acids and ATP

• Deoxyribonucleic Acid ($\text{DNA}$) forms the genetic code in cell nuclei, directing cellular activities and protein synthesis.

• Ribonucleic Acid ($\text{RNA}$) relays genetic instructions to direct cellular amino acid assembly.

• Nucleotide Components:

• Pentose Sugar: Deoxyribose (in $\text{DNA}$) or Ribose (in $\text{RNA}$).

• Phosphate Group: Positively charged bridge linkers ($\text{PO}_4^{2-}$).

• Nitrogenous Bases:

  • Pyrimidines (single-ring structure): Cytosine ($\text{C}$), Thymine ($\text{T}$ -- $\text{DNA}$ only), Uracil ($\text{U}$ -- $\text{RNA}$ only).

  • Purines (double-ring structure): Adenine ($\text{A}$), Guanine ($\text{G}$).

  • DNA Structural Organization:

• Consists of two complementary nucleotide strands twisted into a double helix structure.

• Nitrogenous bases pair via hydrogen bonding across strands:

  • Adenine ($\text{A}$) pairs exclusively with Thymine ($\text{T}$) via $2$ hydrogen bonds.

  • Guanine ($\text{G}$) pairs exclusively with Cytosine ($\text{C}$) via $3$ hydrogen bonds.

  • Comparison of DNA and RNA:

• Nitrogenous Bases: $\text{DNA}$ uses $\text{A}, \text{C}, \text{G}, \text{T}$; $\text{RNA}$ uses $\text{A}, \text{C}, \text{G}, \text{U}$.

• Sugar Component: Deoxyribose in $\text{DNA}$; Ribose in $\text{RNA}$.

• Strand Number: $\text{DNA}$ is double-stranded; $\text{RNA}$ is single-stranded.

• Hydrogen Bonding Base Pairs: $\text{A}=\text{T}$ ($2$ bonds) and $\text{G}\equiv\text{C}$ ($3$ bonds) in $\text{DNA}$; $\text{A}=\text{U}$ ($2$ bonds) and $\text{G}\equiv\text{C}$ ($3$ bonds) in $\text{RNA}$.

• Replication/Synthesis: $\text{DNA}$ is self-replicating; $\text{RNA}$ is transcribed using a $\text{DNA}$ template.

• Function: $\text{DNA}$ encodes genetic information for cellular operation; $\text{RNA}$ carries codes to direct protein synthesis.

• Structural Types: $\text{DNA}$ exists as nuclear and mitochondrial $\text{DNA}$; $\text{RNA}$ exists as messenger $\text{RNA}$ ($\text{mRNA}$), transfer $\text{RNA}$ ($\text{tRNA}$), and ribosomal $\text{RNA}$ ($\text{rRNA}$).

  • Adenosine Triphosphate ($\text{ATP}$):

• The primary chemical energy storage and transfer molecule within biological systems.

• Composition: Adenine nitrogenous base + Ribose sugar (together forming Adenosine) attached to a chain of three phosphate groups.

• Hydrolysis of the terminal high-energy phosphate bond yields Adenosine Diphosphate ($\text{ADP}$), releasing usable cellular energy.

  • Cellular Production of ATP via Respiration:

• Anaerobic Cellular Respiration: Breakdown of glucose without oxygen; yields pyruvic acid and a net total of $2\,\text{ATP}$.

• Aerobic Cellular Respiration: Oxygen-dependent catabolism breaking down pyruvic acid into $\text{CO}_2$ and $\text{H}_2\text{O}$; yields $30 - 32\,\text{ATP}$ per glucose molecule.