1D part 2

Eukaryotic Cells and Organelles

Introduction to Organelles in Eukaryotic Cells

  • Focus on eukaryotic cells, contrasting with prokaryotic cells.

  • Illustrative images to aid understanding of organelles.

Key Organelles Identified

  • Nucleus:

    • Found exclusively in eukaryotic cells.

    • Contains genetic information (DNA) and proteins.

    • DNA and protein complex is referred to as chromatin.

  • Nucleolus:

    • Located within the nucleus; the site of RNA synthesis, particularly ribosomal RNA (rRNA).

    • Distinct from the nucleus, which primarily houses DNA.

  • Nuclear Envelope:

    • Composed of two phospholipid bilayers.

    • Contains pores that facilitate transport of materials in and out of the nucleus.

Ribosomes

  • Function: Site of protein synthesis.

  • Found in all cell types but can vary in size.

  • Appearance: Composed of a large subunit and a small subunit.

  • Can be found either:

    • Free in the cytoplasm.

    • Bound to the rough endoplasmic reticulum (RER).

Endoplasmic Reticulum (ER)

  • Definition: A series of interconnected membranes forming a pathway within the cell.

  • Rough Endoplasmic Reticulum (RER):

    • Characterized by ribosomes on its surface, giving it a rough texture.

    • Functions in protein modification and phospholipid synthesis.

  • Smooth Endoplasmic Reticulum (SER):

    • Lacks ribosomes, features a smooth outer surface.

    • Functions in synthesis of carbohydrates and lipids.

  • Continuous with the nuclear membrane and the RER.

Golgi Apparatus

  • Structure: A series of flattened, interconnected channels.

  • Function:

    • Performs quality control (QC) on proteins and lipids made in the ER.

    • Similar to a shipping hub, where products receive a molecular label for transport.

    • Processes materials received from the RER or SER before dispatching.

  • Transport mechanism:

    • Vesicles bud off from the ER and fuse with the Golgi to deliver content.

    • Final products are packaged in secretory vesicles for transport outside the cell.

Summary of the Endomembrane System

  • The endomembrane system includes:

    • Nucleus with pores and nuclear membrane made of phospholipid bilayers.

    • Endoplasmic Reticulum (both Rough and Smooth), also made of phospholipid membranes.

    • Golgi Body, a membrane structure for processing and shipping cellular products.

Hypothetical Scenario: Insulin Production

  1. Insulin protein synthesis begins with DNA instructions in the nucleus.

  2. Message carried to ribosome from nucleus to produce insulin.

  3. Insulin enters RER for modification.

  4. Protein buds off to Golgi for inspection and shipping.

  5. Protein packaged into secretory vesicle; released into bloodstream.

Other Organelles

  • Lysosomes:

    • Function: Contain digestive enzymes to break down macromolecules like proteins, lipids, and carbohydrates.

    • Act as recycling plants for misfolded or unused cellular debris.

    • Break down macromolecules into component parts (e.g., proteins to amino acids).

  • Peroxisomes:

    • Resemble lysosomes; function to detoxify substances.

    • Example: Breaks down hydrogen peroxide (toxic) into water and oxygen using the enzyme catalase.

    • Potatoes contain catalase; experiment involves breaking down hydrogen peroxide.

  • Vacuoles:

    • Prominent in plant cells, particularly the central vacuole, which stores water and nutrients.

    • Other types include storage vacuoles (smaller) and contractile vacuoles (found in some fungi/protists).

    • Serve a variety of functions depending on the cell type.