Eukaryotic Cells

Eukaryotic Cells

  • Characteristics
    • Have a true nucleus with DNA enclosed within a membrane-bound nucleus.
    • Cytoplasmic organelles are enclosed within a plasma membrane.
    • Nuclear envelope separates the nucleus from the cytoplasm.
  • Structure
    • Nuclear envelope supported by lamins, a type of intermediate filament.
    • Nuclear pore complexes (nucleoporins) within the nuclear envelope control substance exchange.
    • Nucleoplasm is the fluid inside the nucleus, containing chromatin (DNA and protein).

Chromatin and Chromosomes

  • Chromatin
    • Collection of eukaryotic DNA molecules and associated proteins.
    • Eukaryotic chromosomes consist of linear DNA and its proteins.
  • Nucleoli
    • Form around ribosomal RNA genes in the nucleus, site for rRNA synthesis.
    • Ribosomal subunits combine with mRNA to form functional ribosomes.

Ribosomes

  • Molecular machines for protein synthesis; consist of large and small subunits.
  • Eukaryotic ribosomes are larger than prokaryotic (contain 4 types of rRNA and 80+ proteins).
  • Ribosomes can be free in the cytosol or attached to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

  • Smooth and Rough ER
    • Rough ER: Studded with ribosomes, synthesizes proteins (hormones, enzymes).
    • Smooth ER: No ribosomes; synthesizes lipids and detoxifies harmful substances.
  • Interaction: Rough and smooth ER connect, making a continuous membrane system.

Golgi Complex

  • Composed of stacked, flattened membranous sacs (cisternae).
  • Receives proteins from the ER, modifies them, and sorts them into vesicles for transport.
  • Functions in protein secretion, membrane protein incorporation, and lysosome transport.

Lysosomes

  • Membrane-bound vesicles with hydrolytic enzymes for digestion and recycling of complex molecules.
  • Play roles in autophagy and phagocytosis (digestion of engulfed materials).

Mitochondria

  • Site for cellular respiration, enclosed by two bi-layer membranes:
    • Outer Membrane: Smooth with a covering.
    • Inner Membrane: Folded (cristae) to maximize surface area; contains enzymes for ATP production.
  • Support endosymbiont theory: Mitochondria have their own DNA and ribosomes.

Cytoskeleton

  • Provides structure and organization in the cell; consists of:
    • Microtubules: Largest filaments; maintain cell shape, facilitate cell division and organelle transport.
    • Intermediate Filaments: Provide tensile strength and support.
    • Microfilaments: Smallest; involved in cell movement and division.

Plant Cell Structures

  • Chloroplasts: Sites of photosynthesis; contain thylakoid membranes with chlorophyll.
  • Central Vacuole: Stores materials and maintains cell turgor; surrounded by tonoplast.
    • Functions in storage, breakdown of waste, and maintaining osmotic pressure.
  • Cell Wall: Composed mainly of cellulose; provides structure and protection against pathogens.
    • Primary cell wall (soft and flexible) and secondary cell wall (thicker and rigid).

Cell Communication and Structure

  • Cell Adhesion Molecules: Facilitate tissue organization and cell recognition.
  • Cell Junctions: Types include tight junctions (form barriers), anchoring junctions (provide stability), and gap junctions (allow communication).
  • Extracellular Matrix (ECM): Composed of proteins and polysaccharides; supports and protects cells, playing a critical role in tissue structure.

Plant Cell Functionality

  • Plasmodesmata: Channels between plant cells facilitating communication and transport.
  • Plasmolysis: Occurs when cells lose water, leading to decreased turgor pressure and cell shrinkage; reversible under hypotonic conditions.