unit 4 Cell Biology and Histology Review for Exam

Cellular Structure and Function

• Cells are 3D objects; shapes and layers relate to function (e.g., protection, absorption, secretion).

• Major shapes:

  • Squamous: elongated, flat; good for protection (e.g., skin).

  • Cuboidal: cube-like; active in secretion/transport (tube-like, urinary system).

  • Columnar: tall with apical features (cilia/microvilli) for absorption (digestive tract).

• Growth and dimensions: cells are 3D; volume grows faster than surface area as cells enlarge.

  • If the linear dimension L doubles: $SA \propto L^2, \; V \propto L^3$

  • Hence, surface area increases by a factor of 4, volume by a factor of 8.

Cytoplasm, Cytosol, and Fluid Compartments

• Cytoplasm = cytosol + organelles; cytosol is the fluid component.

• Intracellular fluid (ICF) vs extracellular fluid (ECF):

  • In total body water, about $\frac{2}{3}$ is intracellular; $\frac{1}{3}$ is extracellular.

• Intracellular volume depends on cytosolic volume; extracellular fluid surrounds cells and includes interstitial fluid and plasma.

• Two-thirds of total body water is intracellular; one-third is extracellular.

Major Organelles and Their Core Functions

• Nucleus: genetic control center (DNA storage and transcription).

• Ribosomes:

  • Free ribosomes: synthesize proteins for use in cytosol.

  • Bound ribosomes (on rough ER): synthesize proteins for secretion or delivery to organelles.

• Endoplasmic Reticulum (ER):

  • Rough ER: protein synthesis and folding (ribosomes give rough appearance).

  • Smooth ER: lipid synthesis, calcium storage, and roles in muscle contraction coupling.

• Golgi apparatus: modifies, sorts, and packages proteins into transport vesicles for delivery inside or outside the cell.

• Lysosomes: digestive enzymes; break down waste and organelles (autophagy).

• Peroxisomes: fatty acid beta-oxidation and detoxification; contain enzymes for metabolism and detox.

• Proteasomes: degrade unwanted or misfolded proteins into peptides or amino acids.

• Mitochondria:

  • Energy production (ATP).

  • Contain own DNA (mitochondrial DNA).

  • Number varies by tissue; high in energy-demanding cells (e.g., brain, muscle).

  • In muscle, mitochondria cluster for contraction energy; sperm cells have relatively few but strategically placed mitochondria for motility.

• Cytoskeleton (microtubules, etc.): structural support, transport, and anchoring to the plasma membrane; involved in cell junctions.

• Plasma membrane and cell junctions:

  • Junctions anchor cells and enable intercellular communication.

Proteins, Trafficking, and Secretion Pathways

• Secretory pathway:

  • Ribosomes (rough ER) synthesize proteins → Golgi modifies and packages → secretory vesicles released outside the cell or directed to specific destinations.

• Neuronal transport:

  • Proteins synthesized in the soma are packaged and transported to axons and synaptic clefts via transport vesicles.

• Secretory vesicles may carry proteins and ions (e.g., calcium) for signaling and function.

Cell Metabolism and Energy in Context

• Mitochondria provide energy and participate in other vital cellular functions.

• Mitochondrial DNA is separate from nuclear DNA and inherited maternally in many contexts.

Vesicles, Autophagy, and Degradation

• Lysosomes vs Peroxisomes: both are digestive/clean-up organelles, with differences in content and enzymatic composition.

• Proteasomes: regulate protein quality control by degrading unwanted cytosolic/nuclear proteins.

Plasma Membrane, Cell Communication, and Junctions

• Junction types:

  • Tight junctions: seal adjacent cells to prevent leakage.

  • Desmosomes: provide strong adhesion (like a zipper) between cells.

  • Gap junctions: direct electrical/chemical communication between neighboring cells (important in neurons and cardiomyocytes).

• A cell can express multiple junction types to suit tissue-specific needs.

Imaging, Tools, and Visualization

• Immunofluorescence imaging: uses fluorescent antibodies to label specific proteins; visualized with specialized microscopes.

• Light and electron microscopy: higher resolution with larger instruments to view organelles in detail.

• Super-resolution microscopy: exceeds the diffraction limit for clearer, more precise images.

• Foldscope: ultra-cheap, foldable microscope (~$10); educational tool for basic slides; Google Foldscope after class for more info.

Quick Reference and Nomenclature

• Cytoplasm vs cytosol:

  • Cytoplasm = cytosol + organelles.

  • Cytosol = fluid inside cells without organelles.

• Intracellular vs extracellular:

  • ICF vs ECF correspond to fluid compartments inside vs outside cells.

• Erythrocytes (red blood cells): enucleated in maturation; lack nucleus and most organelles; still referred to as erythrocytes.

• Important concept: mutations in a cell can be transmitted to progeny cells during division; addressing mutations at the cellular level can influence propagation.