The Rough Endoplasmic Reticulum & Golgi (Edexcel International A Level Biology)

• 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

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.