Explain how the structure of the Golgi apparatus is related to its function in the processing and secretion of proteins.

IB DP Biology Standard Level (2023 syllabus) — B2.2 Organelles and compartmentalisation · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The Golgi apparatus is a stack of flattened, membrane‑bound cisternae that creates a series of distinct compartments. Proteins are delivered to the cis face from the rough ER in vesicles and, as they move through the cisternae, undergo sequential modifications such as glycosylation or phosphorylation. The trans face then releases the processed proteins in transport vesicles that bud off the Golgi membrane and carry the proteins to their destinations – the plasma membrane, lysosomes or outside the cell via exocytosis. The compartmentalisation of the cisternae provides separate chemical environments, each containing specific enzymes, which allows efficient and accurate modification of proteins without interference from other cellular reactions.

Examiner tips

  • Use the word "cis" and "trans" to show directional flow
  • Mention vesicle budding from the trans face
  • Explain that each cisterna has different enzymes for specific modifications
  • Show that the stack creates distinct compartments

Common mistakes

  • Confusing the cis and trans faces
  • Lacking detail on vesicle budding and destinations
  • Failing to mention the sequential nature of modifications

Mark scheme (4 marks)

  1. The Golgi apparatus consists of a stack of flattened membrane-bound cisternae, providing a series of distinct compartments for the sequential modification of proteins.
  2. Proteins enter the cis face (from the rER via vesicles) and exit from the trans face, ensuring directional flow and correct order of modifications such as glycosylation or phosphorylation.
  3. The Golgi membrane can bud off small transport vesicles that carry processed proteins to their correct destinations, such as the plasma membrane, lysosomes, or outside the cell via exocytosis.
  4. Compartmentalisation within the Golgi cisternae maintains distinct chemical environments (e.g. different enzymes in each cisterna), allowing specific and efficient modifications without interference from other cellular reactions.

Key terms in this question

Golgi apparatus

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