Cell Organelles and Endosymbiotic Theory

Exam and Quiz Information

  • Quiz on Thursday: Will cover material discussed up to that point; less in-depth than the exam, but questions will be knowledge-based.

  • Exam: Material will be labeled and detailed, making it an excellent resource for studying.

    • Strongly suggested study areas: Cells, specifically organelles.

Cell Basics

  • Cells: The basic unit of structure and function within all organisms.

  • Organelles: Components that make up cells.

  • Two kinds of cells:

    • Prokaryotic Cells:

      • Organisms: Bacteria and Archaea.

      • Lack a nucleus and other membrane-bound organelles.

    • Eukaryotic Cells:

      • Organisms: Animals, plants, fungi, protists.

      • Possess a nucleus and other membrane-bound organelles.

The Endomembrane System

  • Definition: A system of membranes internal to and surrounding the eukaryotic cell, functioning to synthesize, modify, and transport proteins and lipids.

  • Components:

    • Cell Nucleus (with nuclear envelope)

    • Endoplasmic Reticulum (ER): Smooth ER and Rough ER

    • Golgi Apparatus

  • Interconnectedness: All components are linked, forming a functional system.

    • Physical Contact: The nucleus is directly connected to the ER by shared membranes.

    • Transport Vesicles: Small, membrane-bound sacs that bud off from one organelle and fuse with another, connecting the ER and the Golgi apparatus.

  • Smooth ER vs. Rough ER:

    • Rough ER: Has ribosomes attached to its surface, giving it a "rough" appearance. Involved in protein synthesis and modification.

    • Smooth ER: Lacks ribosomes. Involved in lipid synthesis, detoxification, and calcium storage.

  • Overall Function: The endomembrane system collectively works to build, package, and synthesize various structures (proteins, lipids) needed throughout the cell.

Mitochondria

  • Function: Often called the "powerhouse of the cell" because it creates energy (ATP) from the food we eat through cellular respiration.

  • Number per Cell: Unlike the nucleus (typically one per cell), the number of mitochondria varies significantly by cell type.

    • Cells that require more energy (e.g., muscle cells, heart cells) will have more mitochondria.

    • A cell can have one up to a couple hundred (100) mitochondria.

  • Structure: Crucial for its function.

    • Double Membrane: Unique feature, as most organelles have only one membrane.

      • Outer Membrane: Smooth, forms the overall kidney bean-like shape.

      • Intermembrane Space: The fluid-filled region between the outer and inner membranes.

      • Inner Membrane: Highly folded into structures called cristae, significantly increasing surface area.

        • This large surface area is vital because the processes that generate energy (e.g., electron transport chain) occur across this membrane.

      • Mitochondrial Matrix: The innermost compartment, enclosed by the inner membrane.

    • Contents of Mitochondrial Matrix:

      • Enzymes: Drive chemical reactions (e.g., Krebs cycle).

      • Mitochondrial DNA (mtDNA): Unique, circular DNA. Discussed below.

      • Ribosomes: For protein synthesis within the mitochondria.

  • Mitochondrial DNA (mtDNA):

    • Location: Not in the nucleus; located within the mitochondrial matrix.

    • Inheritance: Exclusively inherited from the mother (from the egg cell).

    • Shape: Circular, unlike the linear nuclear DNA.

Chloroplasts

  • Function: Create energy from sunlight through the process of photosynthesis.

  • Structure: Similar to mitochondria with a double membrane structure.

    • Double Membrane: Surrounds the organelle.

      • Intermembrane Space: Between the two membranes.

      • Stroma: The fluid-filled space inside the inner membrane.

    • Thylakoid Disks: Internal membrane-bound sacs.

    • Granum (plural: Grana): Stacks of thylakoid disks.

    • Site of Photosynthesis: The thylakoid membranes are where the light-dependent reactions of photosynthesis occur.

  • Chloroplast DNA: Has its own unique, circular DNA, separate from the nuclear DNA.

Endosymbiotic Theory

  • Definition: A widely accepted theory explaining the origin of eukaryotic cells from prokaryotic organisms. It proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by a larger host cell and formed a symbiotic relationship.

  • Terminology Breakdown:

    • Endo-: Meaning