Edexcel International A Level Biology

Revision Notes

3.4 The Rough Endoplasmic Reticulum & Golgi

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Formation of Extracellular Enzymes

  • In cells, many organelles are involved in the production and secretion of proteins
    • Organelles are specialised parts of a cell that carry out a particular function
    • Some organelles are membrane-bound, meaning that they are surrounded by membrane
  • The organelles involved in protein synthesis include
    • Nucleus
      • Transcription of the DNA code occurs here
    • Ribosomes
      • Free ribosomes and those on the RER produce proteins in the process of translation
    • Rough endoplasmic reticulum (RER)
    • Golgi apparatus
    • Cell surface membrane
      • Proteins formed within the cell are secreted here

Rough endoplasmic reticulum

  • Ribosomes on the RER produce proteins that can be secreted out of the cell or become attached to the cell surface membrane
  • Proteins that have been passed into the lumen of the rough endoplasmic reticulum are folded and processed here
    • The term lumen refers to the inside space of the RER
  • Note that free ribosomes found within the cytoplasm make proteins that stay within the cytoplasm rather than being moved to another organelle or being exported from the cell

Golgi apparatus 

  • Processed proteins from the RER are transported to the Golgi apparatus in vesicles which fuse with the Golgi apparatus, releasing the proteins into the Golgi
    • The Golgi apparatus modifies the proteins, preparing them for secretion
  • Proteins that go through the Golgi apparatus are usually
    • Exported, e.g. extracellular enzymes
      • The term extracellular refers to 'outside the cell'
    • Put into lysosomes, e.g. hydrolytic enzymes
    • Delivered to other membrane-bound organelles
  • The modified proteins then leave the Golgi apparatus in vesicles

Organelles protein production (1)

Organelles protein production (2)

The RER and Golgi apparatus are involved with producing, packaging and transporting proteins in a cell. This process can be used to produce and export extracellular enzymes.

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.