Cell Structure and Organization Notes

Cell Structure and Organization

Prokaryotes vs. Eukaryotes

  • Prokaryotic Cells

    • Simple cellular organization
    • Small genome, large proteome
    • Small cell size (1-10 µm)
    • No membrane-bound nucleus
    • Few organelles and compartments
    • Example: Bacteria (e.g., Escherichia coli)

  • Eukaryotic Cells

    • Complex cellular organization
    • Larger genome and proteome
    • Larger cell size (5-100 µm)
    • Membrane-bound nucleus
    • Many organelles and compartments
    • Example: Plant and animal cells

Limits to Cell Size

  • Surface Area to Volume Ratio:
    • As cells grow, volume increases faster than surface area.
    • This limits the size cells can grow while still efficiently exchanging materials with the environment.
  • Prokaryotic Size Limits:
    • Limited by plasma membrane surface area.
  • Eukaryotic Size Limits:
    • More extensive membrane systems improve exchange capabilities.

Cellular Compartmentalization

  • **Organelles: **
    • Defined structures within cells that perform specific functions.
    • Nucleus, cytosol, endomembrane system, semi-autonomous organelles.

The Nucleus

  • Role of the Nucleus:
    • Houses genetic material (DNA).
    • Site of transcription (DNA to RNA).
    • Contains chromatin and nucleolus (for ribosome synthesis).
  • Structure:
    • Enclosed by nuclear envelope (double membrane) with pores for regulated material transport.
  • Nuclear Matrix:
    • Provides structural organization.

Nucleic Acids

  • Types:
    • DNA (Deoxyribonucleic acid)
    • RNA (Ribonucleic acid)
  • Nucleotide Structure:
    • Composed of phosphate, a sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.
  • Base Pairing in DNA:
    • Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

Cytosol and Cytoskeleton

  • Cytosol:
    • Fluid portion of cytoplasm not contained within organelles.
    • Site for metabolic reactions, including protein synthesis.
  • Cytoskeleton Components:
    • Microtubules:
    • Support cell shape, vesicle transport, and chromosome sorting during cell division.
    • Actin Filaments:
    • Involved in muscle contraction, cell shape, and movement.
    • Intermediate Filaments:
    • Provide mechanical strength and maintain cell integrity.

Endomembrane System

  • Components:
    • Nuclear envelope, endoplasmic reticulum (ER), golgi apparatus, lysosomes, peroxisomes, secretory vesicles, vacuoles, and plasma membrane.
  • Functions:
    • Modifications, sorting, and transport of proteins and lipids.
    • Exocytosis and endocytosis for material transport.

Endoplasmic Reticulum (ER)

  • Rough ER:
    • Studded with ribosomes for protein synthesis.
    • Main functions: protein sorting, adding carbohydrates (glycosylation).
  • Smooth ER:
    • Lacks ribosomes; involved in lipid synthesis, detoxifying harmful substances, and calcium ion storage.

Golgi Apparatus

  • Functions in processing and sorting proteins.
  • Formed by stacked membranes with three regions (cis, medial, trans).
  • Involved in secretion pathways and creating vesicles for transport.

Lysosomes and Peroxisomes

  • Lysosomes:
    • Contain enzymes for digesting macromolecules.
    • Function in autophagy (breaking down worn-out cell parts) and extracellular digestion.
  • Peroxisomes:
    • Catalyze reactions that break down molecules, producing hydrogen peroxide but also containing it with specific enzymes (catalase) to prevent damage.

Vacuoles

  • Contain fluid and are prominent in plant cells for storage and maintaining turgor pressure.
  • Example: Contractile vacuoles in protists for osmoregulation, food vacuoles for nutrient storage.

Summary of Key Concepts

  • The distinction between prokaryotic and eukaryotic cells is fundamental to cell biology, with implications for size, structure, and function.
  • Understanding cellular components and their functions is crucial for grasping cellular processes such as metabolism, transport, and communication.