Cell Compartmentalisation (DP IB Biology): Revision Note

Separating The Nucleus & Cytoplasm

• The nucleus is one of the key organelles that distinguishes eukaryotic cells from prokaryotic cells

• It allows many cell processes to take place more efficiently than in prokaryotes

  • Gene transcription and translation are two process that occur in both eukaryotes and prokaryotes

  • In prokaryotes these processes take place simultaneously which allows for rapid responses to an environmental stimuli

  • In eukaryotes these processes occur separately due to the compartmentalisation of the nucleus

    • During transcription, mRNA is formed using a template strand of DNA; the mRNA needs some modification before it can be used for translation

    • Modification can take place in isolation within the nucleus before it comes into contact with a ribosome (this is where translation occurs) unlike in prokaryotes where the mRNA immediately meets a ribosome

    • This step reduces the chance of errors occurring in the mRNA code and therefore in the resulting protein following translation

Compartmentalisation In The Cytoplasm

• The cytoplasm is not considered an organelle, but it's separation from organelles via their membranes is an advantage for the cell

• Organisation of the eukaryotic cell into discrete membrane-bound organelles allows for the separation of incompatible biochemical processes

• This ensures that pathways requiring specific enzymes or metabolites run smoothly and are not at risk from interference from other cell structures or chemicals
  

  • Such reactions can coexist within one organelle by localising conflicting reactions, for example in plant cells a type of enzyme called nitrogenase (used for nitrogen fixation) is particularly sensitive to oxygen so it is positioned in an anaerobic part of the cytoplasm away from aerobic reactions

  • Lysosomes require lytic enzymes which could be harmful to the cell if they were not contained by the lysosome membrane

  • During endocytosis a phagocytic vacuole forms around potentially toxic and harmful substances, such as bacteria; this keeps the contents separate from the cytoplasm and rest of the cell until a lysosome can safely digest the material

Endocytosis and Phagocytosis Diagram

The formation of a phagocytic vacuole ensures harmful substances, such as bacteria, are kept separate from the cytoplasm and the rest of the cell