Lesson 1: Cell Biology

Learning Objectives

• Identify the structural parts of a typical human (eukaryotic) cell.
• Describe the core functions each structure (organelle, membrane, fluid, etc.) performs for overall body health.
• Build conceptual foundations that will later clarify microbiology, immunology and genetics sections.

Course & Reading Context

• Support text: Tortora, Principles of Anatomy and Physiology 3^{\text{rd}} edition (ebook via Massey Library).
• Related paper: 214.101 Normal Body Function.

Big-Picture Definitions

Ethical/Clinical relevance: Understanding “normal” empowers recognition of pathologies (e.g., lysosomal storage diseases, immune defects) and appreciation of microbial diversity.

Three Main Structural Regions

1. Plasma (Cell) Membrane
2. Cytoplasm (cytosol + suspended organelles)
3. Nucleus

Plasma Membrane ― “Double-Glazing”

• Composition: Lipid bilayer (two parallel rows of phospholipids).
• Functions
  • Maintains cell’s shape & integrity.
  • Selectively controls molecular traffic via integral proteins, channels & receptors.
  • Specialised immune cells (e.g.
  • Neutrophils / Macrophages use surface pattern-recognition receptors to bind microbes → engulf by phagocytosis ("vacuum cleaner" analogy).
• Health link: Membrane defects = leakage, auto-immune issues, impaired signalling.

Cytoplasm

• Mostly water, dissolved salts, nutrients.
• Suspension medium for organelles.
• Dynamic staging ground for countless metabolic pathways.

Ribosomes ― “Protein Factories”

• Tiny 2-subunit machines (large + small) made primarily of ribosomal RNA (rRNA).
• Two locations
  • Free in cytosol → create proteins used inside the cell.
  • Bound to Rough ER → translate proteins destined for secretion, membranes or organelles.
• Process: mRNA thread enters → amino acid chain exits (protein synthesis).

Examples of protein output

• Steroid-converting enzymes, mucus constituents, immunoglobulins, “snot,” etc.

Endoplasmic Reticulum (ER)

Overall Layout

Outer extension of the nuclear envelope; labyrinthine tubes & sacs.

Rough ER (RER)

• "Rough" = studded with ribosomes (push-pin imagery).
• Core role: cotranslational protein synthesis + early folding/quality control.

Smooth ER (SER)

• Lacks ribosomes → smooth look.
• Functions
  • Synthesises lipids, phospholipids, steroid hormones.
  • Regulates intracellular Ca^{2+} — vital for muscle contraction & cardiac rhythm.

Mnemonic: Rough = Ribosomes & pRoteins; Smooth = Steroids & Salts (Ca^{2+}).

Golgi Complex ― “Courier Centre / Post Office”

• Stack of flattened sacs (resembles ER cross-section but sits deeper in cytoplasm, not continuous with nucleus).
• Cis face (receiving): accepts new proteins from RER.
• Intrinsic enzymes modify, sort & label cargo.
• Trans face (shipping): dispatches finished vesicles to
  1. Cell surface for secretion (e.g.
     hormones, mucus).
  2. Plasma membrane insertion.
  3. Lysosomes for degradation if faulty.

Process = receive → package → address → ship (two-sided workflow).

Lysosomes ― “Jaffas / Rubbish Dumps”

• Spherical vesicles packed with hydrolytic enzymes (low pH interior).
• Jobs
  • Digest obsolete organelles, mis-folded proteins (autophagy).
  • Fuse with phagosomes in immune cells to kill microbes (autolysis if ruptured).
• Clinical tie-ins
  • Inherited lysosomal storage diseases (enzymatic defects) → toxic buildup → often fatal.
  • Analogy: city garbage workers strike → rubbish overflows, chaos ensues.

Vesicular Traffic Map (Integration Diagram)

1. DNA in nucleus → transcribed to mRNA.
2. mRNA exits nuclear pore → joins ribosome.
3. Protein made, enters RER lumen.
4. Budding transport vesicles carry to Golgi.
5. Golgi sorts →
   • Secretion vesicle → plasma membrane.
   • Membrane vesicle → becomes new membrane patch.
   • Mistake/faulty cargo → lysosome for destruction.
6. External materials entering by endocytosis may merge directly with lysosomes for disassembly.

Mitochondria ― “Bean-Shaped Power Plants”

• Double membrane; inner membrane forms extensive cristae (pastry-style folds) → massive surface area.
• Perform aerobic respiration: glucose + O2 → CO2 + H_2O + ATP (adenosine triphosphate) — universal energy currency.
• Evolutionary note
  • Descended from engulfed bacteria (endosymbiotic theory).
  • Possess circular mitochondrial DNA; inherited maternally.
• Pathophysiology: Mitochondrial mutations → metabolic syndromes, neuro-muscular diseases.

Surface Projections

Cilia ― “Moving Carpets of Hair”

• Short, numerous; beat in coordinated wave.
• Line respiratory tract, sinuses, parts of reproductive & digestive systems.
• Function: propel mucus (laden with immunoglobulins, debris, microbes) outwards → prevents infection & blockage.
• Dysfunction (e.g.
  Primary Ciliary Dyskinesia) → chronic respiratory issues, infertility.

Flagella ― “Turbo Tails”

• Long, usually singular; whip-like rotation due to microtubule motor proteins.
• Human example: sperm flagellum drives long-distance journey to ovum.

Nucleus ― “Headquarters / Library”

• Wrapped by nuclear envelope with protein-rich nuclear pores for traffic control.
• Chromatin = DNA + histone proteins; appears tangled when cell not dividing.
• Nucleolus (ignored for now) = ribosome subunit factory.
• Major flows
  1. Transcription: DNA → mRNA → exits pore.
  2. Regulatory proteins & raw materials travel in.
• During mitosis: chromatin condenses into visible chromosomes (detailed later).

Summary Diagram & Study Tips

• Core organelles: Nucleus, Ribosomes, RER, SER, Golgi, Lysosomes, Mitochondria, Plasma Membrane, Cilia/Flagella.
• Visual learners: red-raw annotated cell cartoons or 3-D apps.
• Verbal learners: summary tables (as on Stream) with two-column “Organelle | Function.”
• Link to medicine: every pathology (inflammation, cancer, infection, genetic disease) can be traced to malfunctions in one or more of these systems.

Key Analogies & Metaphors Recap

• Plasma membrane = “double-glazing” or “double rainbow.”
• Phagocytic immune cell = “vacuum cleaner.”
• Ribosome subunits = “clip together like LEGO.”
• Rough vs. Smooth ER = “nail file” (coarse vs. fine sides).
• Golgi = “courier centre/post office.”
• Lysosome = “Jaffa” full of acid → garbage dump/car-wash for pathogens.
• Mitochondrion = “folded pastry bean” fueled by Red Bull moment.
• Cilia movement = “wave dance.”

Practical / Clinical Connections

1. Immune defence: phagocytosis + lysosome fusion.
2. Hormone secretion: RER → Golgi → exocytosis.
3. Muscle & heart physiology: SER Ca^{2+} handling; mitochondrial ATP supply.
4. Genetic disorders: lysosomal storage, mitochondrial myopathies, ciliary dyskinesia.
5. Pharmacology: many drugs target membrane receptors, ribosomes (antibiotics vs. bacteria), mitochondrial metabolism (chemotherapy), etc.

Final Checklist for Self-Assessment

• Can I sketch a cell and label at least 8 organelles?
• Can I match each organelle to its primary function in one sentence?
• Do I understand how ER, Golgi and lysosomes form a dynamic logistic chain?
• Can I explain why mitochondria have their own DNA and why that matters clinically?
• Can I relate ciliary motion to airway hygiene and flagellar motion to fertility?

If any box remains unchecked, re-read corresponding section or visualise the analogies until the concept sticks.