Cell Biology and Histology Review Guide

Principles of Cell Theory

  • The cell is the smallest structure capable of life processes.

  • All organisms consist of one or more cells.

  • Cells arise only from pre-existing cells.

  • Prokaryotic cells lack an organized nucleus, while Eukaryotic cells possess a well-defined nucleus.

  • Four common structures: Plasma membrane, DNA, Cytoplasm (Cytosol and Organelles), and Ribosomes.

  • Gamete (sex) cells replicate via meiosis; Somatic (body) cells replicate via mitosis.

Cell Membrane Structure and Function

  • Functions: Barrier protection, cytoskeleton anchoring, cell shaping, communication via chemical passage, and transport of molecules/waste.

  • Phospholipid Bilayer: Composed of hydrophilic (lipophobic) heads and hydrophobic (lipophilic) tails.

  • Fluid Mosaic Model: Cholesterol provides structure and flexibility.

  • Integral Proteins: Cross the entire membrane width (e.g., Ion channels, Proton pumps).

  • Peripheral Proteins: Found only on inner or outer surfaces (e.g., Spectrin, which maintains red-cell shape).

  • Hereditary spherocytosis: A condition where red blood cells lack central pallor.

Transport Mechanisms and Membrane Potential

  • Passive Transport: Movement from high to low concentration without ATP.

    • Simple Diffusion.

    • Facilitated Diffusion: Uses protein channels.

    • Osmosis: Water movement toward high solute concentration (Hypertonic: cell shrinks; Isotonic: no net movement; Hypotonic: cell swells).

  • Active Transport: Movement against concentration gradients using ATP.

    • Bulk Transport: Endocytosis (Phagocytosis for solids, Pinocytosis for liquids) and Exocytosis.

  • Resting Membrane Potential (RMPRMP): −70 mV-70\,mV.

  • Sodium-Potassium Pump: Transports 3 Na+3\,Na^+ out and 2 K+2\,K^+ into the cell to maintain electrochemical gradients.

  • Depolarization: Na+Na^+ enters the cell (more positive).

  • Repolarization: K+K^+ exits the cell.

Cellular Organelles and Protein Synthesis

  • Membranous Organelles: Nucleus, mitochondrion, lysosomes, peroxisomes, Endoplasmic reticulum, and Golgi complex.

  • Central Dogma: DNA copying to RNA for protein blueprinting.

  • Transcription: DNA template to mRNA copy.

  • Translation: Ribosomes interpret mRNA; involves Initiation (AUG start codon), Elongation, and Termination (UGA, UAA, or UAG stop codons).

  • DNA Base Pairing: A−TA-T, G−CG-C.

  • RNA Base Pairing: A−UA-U, G−CG-C.

Cellular Respiration and The Cell Cycle

  • Adenosine Triphosphate (ATP): The energy transfer molecule stored in phosphate-phosphate bonds.

  • Equation: C6H12O6+6O2+ADP+Pi→6CO2+6H2O+ATPC_6H_{12}O_6 + 6O_2 + ADP + P_i \rightarrow 6CO_2 + 6H_2O + ATP.

  • Phases: Glycolysis, Krebs cycle, and Electron transport.

  • Cell Cycle: Interphase (S phase for DNA division, G1G_1, and G2G_2) followed by Mitosis.

  • Mitosis Stages: Prophase (chromatin condenses, cross-over occurs), Metaphase (lining up), Anaphase (separation), and Telophase (nuclear membrane forms).

Histology and Tissue Types

  • The four major tissue types are Epithelial, Connective, Muscle, and Nervous.

  • Epithelial Tissue: Avascular, attached via basement membrane; classified by layers (Simple, Stratified, Pseudostratified, Transitional) and shape (Squamous, Cuboidal, Columnar).

  • Connective Tissue: Sparse cells in an extracellular matrix (elastin, collagen, reticular fibers); includes bone, blood, and cartilage.

  • Muscle Tissue:

    • Skeletal: Voluntary, striated, multinuclear.

    • Cardiac: Involuntary, striated, intercalated discs, uninuclear.

    • Smooth: Involuntary, non-striated, found in hollow organs.

  • Nervous Tissue: Consists of neurons (Soma, Dendrites, Axon, Axon Terminals) and neuroglia.

Membranes and Junctions

  • Membrane Types: Cutaneous (skin), Mucous (lines body cavities exposed to exterior), Serous (Parietal and Visceral layers with fluid), and Synovial (connective tissue only, lines joints).

  • Cell Junctions:

    • Tight Junctions: Impermeable barriers.

    • Desmosomes: Structural integrity against mechanical stress.

    • Hemidesmosomes: Anchor cells to the basal lamina using integrins.

    • Gap Junctions: Rapid communication via connexons.

Tissue Modification and Repair

  • Atrophy: Wasting away of tissue.

  • Necrosis: Cell death from injury/disease; Apoptosis: Programmed cell death.

  • Hypertrophy: Increase in cell size; Hyperplasia: Rapid cell division.

  • Metaplasia: Change in tissue nature; Dysplasia: Abnormal cell presence (potential early cancer).

  • Tissue Repair Steps: Inflammation, Proliferation, and Maturation.