Cell Size and Compartmentalization Notes

  • Vesicles can seamlessly form from, travel between, and fuse with membrane-bound organelles bc of membrane fluidity

  • Process that increases cell membrane size: Exocytosis —> vesicles fuse w/ membrane & increase membrane size

  • Process that decreases membrane size: Endocytosis —> vesicles created from the membrane & decreases membrane size

Explain why most cells are small (Concept of SA:V ratio):

  • large cells require lots of nutrients & energy to survive —> generate lots of waste that needs to be excreted

  • transport is most efficient over SHORT distances (if the cell is too large = NOT EFFICIENT)

  • For a cell to be efficient, there needs to be enough cell membrane compared to the size of the cell

  • surface area to volume ratio must be large for cell efficiency

State what relative SA:V ratio equates to high efficiency of cells:

  • cells require a HIGH surface area: volume ratio —> high SA: V ratio = high efficiency

  • SA: V ratio increases if SA increases or V decreases

  • high SA: V ratio = shorter diffusion pathways (higher efficiency)

Two ways to mathematically increase the SA: V ratio —> increase SA OR decrease V

  • high SA: V ratio = shorter diffusion rate —> bc w/ more surface area the diffusion rate is higher (shorter distance)

  • increasing surface area, volume stays constant

  • high ratios: long, skinny, flat shape OR folds in the membrane

  • EX: Villi & Microvilli

  • Larger organisms are multicellular bc they’re made of many small cells (instead of a few large cells) to maintain a high SA:V ratio —> basis for multicellularity

Compartmentalization

Compartmentalization: presence of membrane-bound organelles allows for different functions & processes to occur in different organelles

  • presence of a phospholipid bilayer (membrane) allows separation & different conditions w/in different organelles in the same cell

  • allows for specialization of different organelles & more complex cellular functions (faster reactions)

  • defining characteristic of Eukaryotic cells

  • compartmentalization is necessary bc Lysosomes contain hydrolytic enzymes that need to be packaged to prevent cellular damage

3 Organelles that have double membranes: Nucleus, Mitochondrion, Chloroplasts

  • Endosymbiosis created the double membrane around mitochondria & chloroplasts —> inner membrane was the original prokaryotic membrane

  • Evidence for Endosymbiosis: 70s ribosomes & circular DNA

Nuclear Membrane/Envelope

  • involved in compartmentalization —> surrounds nucleus/protects DNA (regulates gene expression) —> contains pore complexes

  • Pore Complexes: integral proteins —> allow materials to enter/exit the nucleus

  • the outer membrane is continuous w/ the Rough ER