Introductory Physiology and Biomolecules

Overview

Lecture review covers weeks 1–2; quiz spans five chapters, 25 questions, 40 lecture points.
Focused topics: physiology basics, homeostasis, biomolecules, cell structure, enzymes, metabolism, membrane transport, genetics, and lab concepts.

Physiology: study of normal functioning of living organisms and component parts.
Homeostasis: maintenance of a relatively stable internal environment by returning variables to set points.
Negative feedback: restores homeostasis (e.g., thermoregulation, blood glucose via insulin).
Positive feedback: pushes system away from set point (e.g., childbirth via oxytocin, blood clotting).

"Structure determines function": molecular shape (e.g., protein conformation) dictates activity.

Humans mainly built from carbon atoms; carbon central in lipids, proteins, nucleic acids.
Four major biomolecules: carbohydrates, lipids, proteins, nucleic acids.
- Building blocks: monosaccharides (carbs), fatty acids (lipids), amino acids (proteins), nucleotides (nucleic acids).

Basic unit of life: the cell.
Cell membrane: semi-permeable phospholipid bilayer separating inside/outside.
Organelles and main functions:
- Mitochondria: ATP production.
- Ribosomes: protein synthesis.
- Smooth ER: lipid synthesis.

Intracellular fluid (ICF): inside cells; higher potassium concentration.
Extracellular fluid (ECF): outside cells; higher sodium and chloride concentration.
Osmotic equilibrium: water freely crosses until water distribution equal.
Chemical disequilibrium: solute concentrations differ between compartments.

Energy: capacity to do work.
Types of work: chemical (make/break bonds), transport (move ions/molecules), mechanical (move organelles/cells).
First law (conservation): energy neither created nor destroyed, only transformed.
Second law (entropy): systems tend toward disorder.

Enzymes: proteins (or RNA) that catalyze reactions by lowering activation energy.
Enzymes remain unchanged and can act repeatedly.
Cofactors/coenzymes: nonprotein molecules or ions required for enzyme activity (e.g., vitamins, Mg2+, Zn2+).
Allosteric regulation:
- Cofactor binds active site and is required for activity.
- Allosteric activator/inhibitor binds elsewhere and changes protein conformation.
Competitive inhibitor: binds active site, blocks substrate.
Noncompetitive/allosteric inhibitor: binds elsewhere, alters active site shape.
Factors affecting enzyme activity: temperature, pH, substrate concentration, enzyme concentration.
Proenzymes (zymogens): synthesized inactive, activated by proteolytic cleavage when needed.

Metabolism: all chemical reactions in an organism.
- Catabolism: breakdown, releases energy.
- Anabolism: synthesis, consumes energy.
Cellular respiration overview:
- Glycolysis: cytosol, anaerobic, glucose → 2 pyruvate.
- Pyruvate → acetyl-CoA in mitochondria (requires oxygen ultimately).
- Citric acid (Krebs) cycle: acetyl-CoA carbons processed in mitochondrial matrix; produces NADH and FADH2.
- Electron transport chain (inner mitochondrial membrane): electron transfer pumps H+ to create gradient.
- ATP synthase: H+ flows down gradient to synthesize ATP.
- Oxygen is final electron acceptor; combines with H+ to form water.
ATP yield: typically ~36–38 ATP per glucose (varies).

DNA contains genes (segments encoding traits).
Transcription: DNA → RNA (occurs in nucleus).
Translation: RNA → protein (occurs in cytoplasm at ribosomes/ER).
Base pairing:
- DNA: A ↔ T, G ↔ C.
- RNA: A ↔ U, G ↔ C.
Codons: three-nucleotide mRNA sequences specify amino acids.
Post-translational modifications: processing after translation (e.g., proteolytic activation, cofactor addition) to yield mature functional proteins.
Alternative splicing: removes introns, arranges exons differently to produce multiple proteins from one gene.

Nucleotides: building blocks of nucleic acids.
Functions: energy carriers (ATP = adenosine triphosphate) and genetic material components (DNA/RNA).

Primary active transporter of greatest importance: Na+/K+ ATPase (sodium-potassium pump).
- Moves 3 Na+ out, 2 K+ in per ATP hydrolyzed.
Resting membrane potential: ~ -70 mV in excitable cells; mainly due to K+ leak.
Membrane and fluids are electrically neutral overall; potential difference across membrane matters.

Chemically gated channels: open/close in response to chemical ligands or intracellular messengers.
Voltage-gated channels: open/close in response to membrane potential changes.
Mechanically gated channels: respond to physical forces (pressure, stretch, tension).
Ligand-gated channels: open when specific ligands bind; allow ion flow.

Passive transport (no ATP): simple diffusion, facilitated diffusion, osmosis.
- Simple diffusion: molecules move high → low concentration.
- Facilitated diffusion: proteins (channels, carriers) aid movement down electrochemical gradients.
- Aquaporins: water channels enabling osmosis.
Active transport (requires ATP): primary and secondary active transport, vesicular transport.
- Primary: direct ATP use (e.g., Na+/K+ pump).
- Secondary: uses gradients created by ATP indirectly.
- Vesicular: endocytosis, exocytosis (ATP-dependent).

Apical (mucosal) membrane: faces lumen of organ.
Basolateral (serosal) membrane: faces extracellular fluid/blood.
Absorption: movement from lumen → extracellular fluid (e.g., intestine → blood).
Secretion: movement from extracellular fluid → lumen (e.g., blood → intestine/nephron lumen).

Tonicity: effect of solution on cell volume (shape).
- Isotonic: no net volume change.
- Hypertonic: solution has higher solute; water exits cell → crenation (shrink).
- Hypotonic: solution has lower solute; water enters → swelling, possible lysis.
Red blood cell morphology indicates health; normal is biconcave shape.

Phagocytosis: cell "eating" large particles; membrane encloses particle into phagosome.
Pinocytosis: "cell drinking" fluids and solutes.
Receptor-mediated endocytosis: ligand binds receptor; induces vesicle formation for specific uptake.

Memorize key definitions: homeostasis, feedback types, enzyme roles, metabolism steps.
Know compartment ion distributions: more K+ inside; more Na+ and Cl- outside.
Practice converting DNA ↔ RNA (T ↔ U) and transcribing codons to amino acids.
Distinguish passive vs. active transport and examples (simple vs. facilitated diffusion).
Understand Na+/K+ pump stoichiometry and its role in resting membrane potential.
Review enzyme regulation: cofactors, allosteric control, competitive vs. noncompetitive inhibition.
Work through sample lab problems involving permeability, osmosis, and diffusion calculations.