Module 17 - Cellular Compartments and Protein Sorting

Question 1

Explain why organelles are structural and functional compartments

Answer 1

Organelles are separately enclosed within their own lipid bilayer, forming an enclosed structure within the cytoplasm. Each of these organelles has their own specialized function aided by enzymes or compounds inside them.

Question 2

Define topological equivalence.

Answer 2

Topologically equivalent refers to how molecules can pass between these organelles without physically passing a membrane. Organelles that are topologically equivalent are endosome, peroxisome, lysosome, golgi apparatus, ER.

Question 3

Describe the organisation of inner and outer leaflets of membrane bilayer during budding and fusion

Answer 3

The orientation of the inner and outer bilayer is maintained during these processes. The bilayers that are exposed to the cytoplasm will fuse together and vice versa.

Question 4

Describe the dual problems of access and targeting for moving proteins between cellular compartments

Answer 4

• Access (topology): getting from cytosol into various compartments
• Targeting: getting into the right compartment

Question 5

Define three mechanisms for moving proteins from one compartment to another

Answer 5

1. Gated Transport: movement between cytosol and nucleus (topologically equivalent)
2. Transmembrane transport: protein translocators (not topologically equivalent)
3. Vesicular transport: between topologically equivalent compartments (issue of targeting)

Question 6

Explain how proteins can move between organelles that are topologically equivalent.

Answer 6

Organelles that are topologially equivalent can transform into another by vesicle budding and fusion. This allows for protein inside the compartments to “spill” into another organelle without actually passing through the membrane.