Protein secretory pathway

Question 1

rough endoplasmic reticulum (RER) 

Answer 1

a membranous organelle shaped
like a series of connected, flattened
cylinders that folds and transports
proteins via its attached ribosomes

Question 2

Golgi apparatus

Answer 2

an organelle
made of flattened sacs of
membrane involved in modifying,
sorting, and packaging proteins.

Question 3

Step 1 (ribosome)

Answer 3

The ribosomes are the sites of protein synthesis. They assemble polypeptide
chains from amino acids by translating mRNA.

Question 4

Step 2 (RER)

Answer 4

If a protein is destined to be secreted, the ribosome synthesising it is usually
attached to the rough endoplasmic reticulum rather than being free in the
cytosol. The environment inside the rough endoplasmic reticulum allows for the correct folding of the newly formed polypeptide chain before being passed to the Golgi apparatus.

Question 5

Step 3 (transport vesicle)

Answer 5

A transport vesicle containing the protein buds off the rough endoplasmic reticulum and travels to the Golgi apparatus. The vesicle fuses with the Golgi membrane and releases the protein into its lumen.

Question 6

Step 4 (Golgi apparatus)

Answer 6

Proteins can have chemical groups (e.g. sugar molecules) added or removed at the Golgi apparatus, where they are often packaged into secretory vesicles for export or released directly into the cytosol for use by the cell

Question 7

Step 5 (secretory vesicle)

Answer 7

Secretory vesicles containing proteins for export bud off the Golgi apparatus and travel through the cytoplasm, fusing with the plasma membrane. This releases the proteins contained from within, into the extracellular environment through the process of exocytosis.