Chapter 2 Notes: Reaction Rate and Biomolecules

Reaction Rate and Biomolecules

  • Chapter focus: reaction rate as the basis of chemical reaction and molecular motion; reactions occur when molecules collide with sufficient force (collision theory).

  • Factors that speed up reactions:

    • Concentration of reactants
    • Temperature
    • Higher temperature increases reaction rate (example: sugar dissolves faster in hot water).

  • Catalysts and enzymes:

    • Catalyst: substance that temporarily bonds to reactants, holds them in a favorable position to react, and may change the reaction pathway to favor products.
    • Enzymes are biological catalysts; all enzymes are proteins, but not all proteins are enzymes.
    • Enzymes work by lowering the activation energy of a reaction.
    • Important reminder from the transcript: enzyme speed is tied to temperature and pH; extreme heat or unfavorable pH can denature enzymes.

  • Catabolic vs anabolic reactions:

    • Catabolic reactions break chemical bonds to release energy (the transcript uses the term “cannibalism” as a mistaken word).
    • Anabolic reactions input energy to build up molecules.

  • Oxidation–reduction (redox) briefly mentioned; the deep chemistry is not the focus for anatomy/physiology in this chapter.

  • Organic compounds (four primary classes):

    • Carbohydrates
    • Lipids
    • Proteins
    • Nucleic acids

  • Carbohydrates: structure and classification

    • Monosaccharides (simple sugars): examples include glucose, galactose, fructose.
    • Saccharide meaning: monosaccharide = single sugar; disaccharide (e.g., sucrose) = two sugars; oligosaccharide = chain of three or more monosaccharides; polysaccharide = long chains (often ≥50 units).
    • Common monosaccharide: glucose = blood sugar.
    • Oligosaccharides and polysaccharides in humans:
    • Glycogen: energy storage polysaccharide in animals; stored mainly in liver after meals and in muscle for activity; used for energy during exercise.
    • Starch: energy storage polysaccharide in plants; cellulose: plant cell wall component (indigestible by humans; dietary fiber).
    • Carbohydrate abbreviations and terms:
    • Monosaccharide (glucose, galactose, fructose)
    • Oligosaccharide (short chains of 3+ monosaccharides; transcript notes at least 10 in one place, but typical definition is 3–9)
    • Polysaccharide: long chains (e.g., glycogen, starch, cellulose)
    • Glycogen distribution and function:
    • Liver glycogen stores after a meal to maintain blood glucose levels.
    • Muscle glycogen used for energy during movement and activity.
    • Lipids and carbohydrates in the body:
    • Carbohydrates are quickly mobilized as glucose; oxidation of glucose yields ATP.
    • Conjugated carbohydrates include glycoproteins and glycolipids; glycogen is a prominent example.

  • Lipids: structure, types, and functions

    • Lipids are hydrophobic (hydro- means water; -phobic means fear of water);
    • Lipids are composed mainly of carbon, hydrogen, and oxygen with a high hydrogen-to-oxygen ratio and higher calorie per gram than carbohydrates.
    • Five primary lipid types discussed (as per the transcript’s framing):
    • Fatty acids
    • Triglycerides
    • Phospholipids
    • Steroids (including cholesterol and steroid hormones such as estrogen/progesterone)
    • Eicosanoids (bioactive lipids derived from arachidonic acid)
    • Fatty acids:
    • Saturated vs unsaturated vs polyunsaturated:
      • Saturated: full of hydrogen, no double bonds.
      • Unsaturated: one or more double bonds (cis configuration is common; trans fats have trans double bonds and are more resistant to enzymatic breakdown, contributing to atherosclerosis risk).
    • Essential fatty acids: must be obtained from the diet; body cannot synthesize them.
    • Triglycerides: energy storage form; formed by glycerol + 3 fatty acids via dehydration synthesis; can be liquid (oil) at room temperature when unsaturated, or solid (fat) when saturated at room temperature.
    • Phospholipids: similar to fats but with a phosphate-containing head; amphiphilic (hydrophilic head, hydrophobic tails); structural foundation of cell membranes.
    • Steroids and cholesterol:
    • Cholesterol is a parent steroid; used to synthesize other steroids and hormones (e.g., cortisol); a portion is from the diet and a portion is synthesized endogenously.
    • Cholesterol is a key component of cell membranes and a precursor to steroid hormones.
    • Lipids and health terms:
    • HDL (high-density lipoprotein) and LDL (low-density lipoprotein) mentioned as “good” and “bad” cholesterol, relevant in later chapters.

  • Proteins: structure, function, and importance

    • Proteins are described as the most versatile body molecules; built from amino acids via peptide bonds.
    • Amino acids: 20 standard amino acids; all share a common backbone but differ in their side chain (R group).
    • Protein structure levels:
    • Primary structure: linear sequence of amino acids.
    • Secondary structure: alpha helix and beta sheets held together by hydrogen bonds (between peptide bond atoms).
    • Tertiary structure: three-dimensional folding of a single polypeptide including interactions among side chains.
    • Quaternary structure: two or more polypeptide chains associated (e.g., hemoglobin with four chains).
    • Denaturation: disruption of a protein’s three-dimensional structure by heat or pH, altering function (example: cooking an egg).
    • Conjugated proteins and prosthetic groups (e.g., heme in hemoglobin).
    • Protein functions in the body:
    • Enzymes as catalysts; all enzymes are proteins, but not all proteins are enzymes.
    • Structural proteins (e.g., collagen, keratin) providing support.
    • Carrier and transport proteins; membrane channels and carriers regulate passage across membranes.
    • Receptors and signaling molecules; ligands bind receptors to signal cells.
    • Immunity: antibodies are protein components of the immune system.
    • Enzymes in detail:
    • Enzymes lower the activation energy of reactions and act as biological catalysts.
    • Substrate binds to the enzyme’s active site to form an enzyme–substrate complex; highly specific – like a key fitting a lock.
    • Enzymes can be denatured by heat or extreme pH; optimal pH varies by enzyme and location (e.g., saliva ~ pH 7.0, pepsin in stomach ~ pH 2).
    • Cofactors and coenzymes:
      • Cofactors are non-protein helpers; inorganic cofactors include minerals like iron, zinc, magnesium, calcium.
      • Coenzymes are organic molecules, often derived from vitamins (e.g., B vitamins); they assist enzymes by carrying chemical groups or electrons.
      • Thiamine (vitamin B1) can act as a coenzyme (e.g., thiamine pyrophosphate) in certain reactions; B vitamins are water-soluble and not stored in the body; excess is excreted by kidneys.
    • Allosteric regulation: cofactors can induce conformational changes in enzymes to alter activity and substrate affinity; allosteric control can make the active site more or less accessible.
    • Adenosine triphosphate (ATP) and energy transfer:
      • ATP is the primary energy currency; energy stored in high-energy phosphate bonds.
      • Hydrolysis of ATP releases energy: ATP + H2O ightarrow ADP + Pi + ext{energy}
      • The third phosphate bond is the high-energy bond involved in energy transfer; ADP can be re-phosphorylated back to ATP using energy from cellular respiration, often in mitochondria.
    • Kinases are enzymes that transfer phosphate groups from ATP to target molecules (phosphorylation), coupling energy transfer to metabolic pathways.
    • A note on ATP/ADP cycling: in the presence of oxygen, glucose oxidation in mitochondria yields substantial ATP; without oxygen, ATP production is limited and energy supply declines rapidly.
    • Cyclic adenosine monophosphate (cyclic AMP or cAMP): a second messenger formed from ATP; plays a key role in intracellular signaling by activating downstream pathways.

  • Nucleotides and nucleic acids

    • Nucleotides include ATP, GTP, and other nucleotide triphosphates; ATP is a nucleotide triphosphate used for energy transfer.
    • ATP structure (not required to memorize detailed structures here): adenosine attached to three phosphate groups; energy stored in the phosphate bonds.
    • Nucleotide roles in metabolism:
    • ATP is the energy transfer molecule; ADP can be formed by ATP hydrolysis and then recharged by cellular pathways.
    • ADP cycling with ATP is essential for continuous energy supply; without ongoing production, cellular energy would quickly deplete.
    • Nucleotides also participate in signaling (e.g., cyclic AMP as a second messenger) and in genetic material (DNA and RNA).
    • DNA and RNA are mentioned in passing as nuclear components of genetics and transcriptional processes; chapter 4 will revisit these topics in more detail.

  • Key concepts to connect to physiology

    • Energy flow and metabolism hinge on enzymes lowering activation energy to enable faster reactions under physiological conditions (37°C, near-neutral pH in many tissues).
    • The extracellular and intracellular environments shape enzyme activity via cofactors, coenzymes, pH, and temperature.
    • Lipids provide long-term energy storage, insulation, and membrane structure (phospholipids) and act as signaling molecules (steroids and eicosanoids).
    • Carbohydrates supply rapid energy as glucose and glycogen; polysaccharides provide storage (glycogen) and structural roles (cellulose in plants).
    • Proteins are central to structure, function, signaling, and catalysis; their activity depends on correct folding and interactions; denaturation disrupts function.

  • Practical exam orientation and reminders

    • Memorize the general definitions and relationships (monomer vs polymer, dehydration synthesis vs hydrolysis, hydrophobic vs hydrophilic, primary/secondary/tertiary/quaternary structures, enzyme–substrate specificity).
    • Understand how to explain activation energy lowering with an enzyme using the binding of substrate to the active site and the resulting enzyme–substrate complex.
    • Be able to describe the roles of cofactors and coenzymes, especially B vitamins in energy metabolism and enzyme function.
    • Recall the basic lipid concepts: triglycerides, phospholipids, cholesterol, saturations, cis/trans configurations, and the functional importance of phospholipids in membranes.

  • Quick, test-ready recap

    • Activation energy concept and enzyme function: E + S ⇌ ES → E + P; enzymes lower Ea.
    • Dehydration synthesis vs hydrolysis: Monomer + Monomer → (loss of H2O) Dimer; Polymer + H2O → Monomer(s).
    • Carbohydrate classifications: monosaccharide, disaccharide (e.g., sucrose), oligosaccharide, polysaccharide (glycogen, starch, cellulose).
    • Lipid characteristics: hydrophobic, five types (fatty acids, triglycerides, phospholipids, steroids, eicosanoids); saturated vs unsaturated; trans fats and health implications; membrane role of phospholipids; cholesterol as a steroid precursor.
    • Protein structure and function: primary–quaternary structures; denaturation; enzymes as proteins; cofactors/coenzymes; B vitamins; ATP/ADP cycling; cAMP as second messenger.

  • Final note

    • The transcript emphasizes that many themes recur across chapters; a solid grasp of these foundational ideas will support understanding in later topics (e.g., chapter 3 and beyond).