Cell Biology: Intracellular Organization Quiz

Intracellular Organization and Protein Sorting

• Macromolecules and their associated activities are spatially separated within cells.
• Eukaryotic cells are subdivided into membrane-enclosed compartments (organelles).
• Examples of organelles include the endoplasmic reticulum, Golgi apparatus, lysosomes, plastids, and mitochondria. These are sometimes further divided by internal membranes.
• Biomolecular condensates are dynamic assemblies of macromolecules. They can specialize as factories or storage centers.
• The nucleolus is a biomolecular condensate not enclosed by a membrane.
• Animal cells have about 10 billion protein molecules of about 10,000 kinds.
• Protein synthesis starts in the cytosol (outside the membrane-enclosed organelles).
• Proteins are specifically delivered to the organelles that need them.
• Organelle surfaces have unique protein and lipid compositions used to target protein and lipid deliveries.
• Eukaryotic cells have the same basic set of membrane-enclosed organelles.
• These compartments increase biochemical reaction areas and functionally specialize different spaces inside cells.
• Compartments allow reactions requiring different conditions to occur simultaneously, without interfering.
• Specific organelles exist for specific biochemical functions. Rough and smooth ER, Golgi, lysosomes, mitochondria, endosomes, and peroxisomes.

Relative Volumes of Intracellular Compartments

• In a liver cell, cytosol occupies about 54% of the total cell volume.
• Other major intracellular compartment volumes include: mitochondria (22%), rough ER (9%), smooth ER (5%), Golgi (6%), nucleus (1%), peroxisomes (1%), lysosomes (1%), and endosomes (1%).

Relative Membrane Types

• In liver cells, the plasma membrane makes up a small percentage (2%) of the total membrane surface.
• The rough endoplasmic reticulum accounts for a large percentage (35%), followed by the smooth ER (16%) and Golgi (7%).
• Mitochondria (7%) and other membrane systems have smaller percentages.

Evolutionary Origins of Organelles

• Eukaryotic cells possibly originated from the joining of an anaerobic archaeon and an aerobic bacterium.
• Cell migration may have played a crucial role in this process.
• Protrusions likely stabilized internal membranes.
• The symbiotic relationship with an aerobic bacterium likely enabled the archaeon to increase in size.
• These protrusions may have fused ultimately leading to internal membranes, primordial nucleus, and an endosymbiont.

Topological Relationships of Organelles

• The lumen of internal compartments in eukaryotes is topologically equivalent to extracellular space.
• Endosymbiosis lead to mitochondria.
• Internal compartments progressively specialized into organelles.
• Organelles can exchange materials/information through vesicular transport.

Topologically Equivalent Compartments

• Molecules can move between topologically equivalent compartments via transport vesicles.
• The transfer permits communication among compartments.

Intracellular Compartments in Eukaryotic Cells

• The major compartments are categorized into three groups: nucleus & cytosol, secretory/endocytic pathways, and endosymbiotic organelles (e.g., mitochondria, plastids).

Macromolecules Segregation

• Macromolecules can selectively segregate without a surrounding membrane.
• Scaffolds (nucleic acids or proteins) create condensates.
• Clients are specific molecules attracted to the scaffold via weak binding interactions.
• Concentration of components helps them function in that local region.

Biomolecular Condensates

• These are diverse, with different roles. Examples include nucleolus, pyrenoids, stress granules, P-granules, and others.

Biomolecular Condensates and Factories

• Condensates can act as biochemical factories. The pyrenoid example concentrates proteins involved in carbon fixation.

Biomolecular Condensate Response to Needs

• Formation and stability depend on weak interactions that overcome entropy.
• Small changes can alter formation, and physical properties.
• Need-based activation or deactivation of signaling components can lead to condensation or disassembly.

Test your knowledge on the intricate organization of eukaryotic cells and the process of protein sorting within organelles. This quiz covers key concepts such as the function of various organelles, the role of biomolecular condensates, and the mechanisms behind protein delivery in cells. Perfect for students studying cell biology or related topics.