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

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

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.