Cell_Structure_and_Function (1)

Overview of Cell Structure and Function

Learning Outcomes

• Compare and Contrast: General features of prokaryotic and eukaryotic cells.

• Proteome Understanding: Explain how the proteome underlies the structure and function of a cell.

• Cell Size and Shape Analysis: Analyze how cell size and shape affect the surface area/volume ratio.

Factors Determining Cell Structure and Function

1. Matter

   • Living organisms consist of atoms, molecules, and macromolecules.

   • Unique sets of molecules are synthesized by each cell contributing to its functions.

2. Energy

   • Energy is necessary for producing molecules and executing cellular functions.

   • Detailed discussion in Chapters 6-8.

3. Organization

   • Cells are structured with components located at specific sites; not a random collection.

   • Example: Muscle cells show similarities in structure between individuals.

   • Proteins interact like building blocks, forming intricate cell structures.

4. Information (Genetic Material)

   • Genetic material (DNA) acts as the blueprint of life; crucial for cell function and heredity.

   • Every organism has a unique genome; cells inherit copies during division.

   • Genes produce proteins that primarily determine cell structure and function.

Prokaryotic Cells - Simple Structure

• Definition: Prokaryotic cells have no membrane-enclosed nucleus; term derives from Greek words for "before kernel."

• Types: Bacteria and archaea are the two main groups of prokaryotes; they are generally small and unicellular.

• Key Structures:

  • Nucleoid: Contains DNA.

  • Plasma Membrane: Encloses cytoplasm.

  • Cell Wall: Provides support and protection; varies in composition.

  • Glycocalyx: Gelatinous covering for protection and moisture retention.

  • Ribosomes: Synthesize polypeptides.

  • Flagella: Enable motility.

  • Pili: Allow attachment to surfaces.

Eukaryotic Cells - Compartmentalized Structure

• Characteristics: Organelle structures encased by internal membranes.

• Types of Eukaryotes: Protists, fungi, plants, and animals.

• Example Structures:

  • Nucleus: Contains most genetic material; organized and expressed.

  • Endoplasmic Reticulum (ER): Rough ER for protein sorting, Smooth ER for detoxification.

  • Golgi Apparatus: Modifies, sorts, and secretes proteins.

  • Mitochondria: ATP synthesis site.

  • Peroxisomes: Break down harmful substances.

  • Cytoskeleton: Protein filaments for shape and movement.

  • Lysosomes: Degrade macromolecules.

  • Chloroplasts (in plants): Site of photosynthesis.

  • Central Vacuole (in plants): Storage and regulation of cell volume.

Droplet Organelles

• Definition: Newly discovered organelles formed via liquid-liquid phase separation of aggregated proteins and RNA.

• Function:

  • Bring molecules together for complex formation, e.g., ribosomal subunits in nucleolus.

  • Create chemically distinct environments that could affect molecular interactions.

Proteome and Cell Differentiation

• Proteome vs. Genome: Genome contains all genetic information, while proteome is the complete set of proteins expressed by a cell.

• Cellular Diversity: Different cell types (e.g., skin cells vs. neurons) have unique protein expressions:

  • Certain proteins might not be produced in all cell types.

  • Even shared proteins may have different expression levels across cell types.

Surface Area and Volume Ratio

• Key Concept: Most cells maintain a small size; internal volume must match nutrient import and waste export abilities.

  • Surface area/volume ratio diminishes as cell size increases.

  • Larger organisms have more cells, not necessarily larger ones.

• Implication for Cell Function: High surface area/volume ratio is critical for efficient nutrient uptake and waste disposal.

Calculating Volume and Surface Area

• Formulas:

  • Sphere: Volume = (\frac{4}{3} \pi r^3); Surface area = (4 \pi r^2)

  • Cylinder (as an example of a different shape): Volume = (r^2h); Surface area = (2\pi r^2 + 2\pi rh)

• Illustration Example:

  • Radius of 3 μm for two-cell shapes; one cell is cylindrical, the other spherical with radius of 3 μm leading to different volume/surface area ratios, highlighting the significance of shapes in biological structures.