Cell Biology Lecture Notes

Structural Elements of Cells

• Membranes

  • Membranes are fluid-like structures that do not provide significant structural support for cells.
  • They facilitate a barrier for movement and communication between internal and external environments.

• Cytoskeleton

  • Provides mechanical strength and structure.
  • Composed of various filaments that support shape and organization within the cell.

Cell Junctions

• Tight Junctions

  • Predominantly found in epithelial cells.
  • Form continuous strands around cells, creating a barrier to solute movement between cells.
  • Separate apical (top) and basal (bottom) surface proteins to maintain cell polarity.

• Adherens Junctions

  • Connect cells to one another and to the cytoskeleton.
  • Composed of linker proteins that integrate and connect the cytoskeleton of adjacent cells.
  • Essential for mechanical strength and maintaining tissue integrity during movement.

• Desmosomes

  • Spot-like structures that provide localized adhesion between cells.
  • Resists shear and tensile forces due to their attaching to intermediate filaments (like keratin).

• Hemidesmosomes

  • Connect epithelial cells to the underlying extracellular matrix/basal lamina.
  • Use integrins to secure cells and prevent detachment.

Gap Junctions

• Facilitate communication between neighboring cells.
• Comprised of pore-like structures that allow ions and small molecules to pass between cells.
• Important in coordinating cellular functions and responses across tissues, e.g., cardiac muscle.

Understanding Mechanical Strength

• Strong cell-to-cell connections (like adherens junctions and desmosomes) are essential for tissue integrity, particularly in response to physical stress, such as muscle contraction.
• The cytoskeleton's connection allows for flexibility and strength during cell movement.

Embryonic Development

• Processes like gastrulation (folding of cells) and neurulation (formation of the neural tube) rely heavily on the mechanical properties of cell junctions for proper formation of tissues and organs.

Biochemical Aspects of Cells

• Shift from structural properties to biochemical functions, focusing on small organic molecules leading to macromolecules (proteins, carbohydrates, lipids).
• Water constitutes about 70% of cell weight, serving as a solvent for biochemical reactions.

Small Organic Molecules

• Sugars

  • Source of energy and building blocks for polysaccharides and nucleic acids.
  • Classes include monosaccharides (like glucose) and disaccharides (like sucrose).

• Fatty Acids

  • Subunits of lipids, important for storing energy more densely than carbohydrates.
  • Classifications include saturated (no double bonds) and unsaturated (one or more double bonds), affecting membrane fluidity and energy release.

• Amino Acids

  • Building blocks of proteins, classified into essential (must be consumed) and non-essential categories.
  • Each amino acid consists of a central carbon, an amine group, a carboxylic acid, and a variable R group (side chain).

• Nucleotides

  • Building blocks of nucleic acids (DNA, RNA) and serve as energy carriers (ATP).
  • Comprised of a nitrogenous base, a sugar, and phosphate groups.

Clinical Significance of Molecular Disruptions

• Disruptions in junctions (hemidesmosomes) can lead to significant health issues, highlighting the importance of structural integrity in cellular function.

• Metabolic disorders, such as hypoglycemia (low glucose levels) and amino acid deficiencies, showcase how molecular balance impacts animal health and growth.

• Nutrient absorption and utilization depend heavily on biochemical pathways involving small molecules and their interactions with larger macromolecules.

• Key Takeaway: Understanding cell structure, types of junctions, and biochemical principles leads to a deeper insight into function, health impacts, and the physiological roles of these cellular components.