Transmembrane proteins, Golgi, COP (Golgi complex)

Question 1

ER to Golgi Complex

Answer 1

• Material moves from ER to Golgi and then to other compartments and the plasma membrane in a proximal to distal direction

Question 2

Structure of the Golgi complex:

Answer 2

• Smooth, flattened, disk-like cisternae (~0.5-1 micron in diameter).
• ~8 (or fewer) cisternae/stack—range from a few to several 1000 stacks per cell.
• Curved like a shallow bowl.
• Shows polarity: cis–medial–trans cisternae.
• Cisternae are biochemically unique.
• Membrane supported by protein skeleton (actin, spectrin).
• Scaffold linked to motor proteins that direct movement of vesicles into and out of the Golgi

Question 3

Golgi complex: Why the structural difference?

Answer 3

• CGN acts as a sorting station (i.e., sorts whether proteins should continue on to the next Golgi station or be shipped back to the ER).
• TGN sorts protein into different types of vesicles—vesicles go to plasma membrane or other intracellular destinations (e.g. lysosomes)

Question 4

Biochemical Diversity of Golgi complex:

Answer 4

• Proteins are modified step-wise as they traverse the Golgi.
• Different cisternae of the Golgi contain different enzymes that modify proteins.
• The differential staining of the Golgi cisternae reflects their biochemical differences
• Golgi is processing plant of the cell.
• In addition to sorting, the Golgi is also involved in synthesis of polysaccharides and specific modification of proteins and lipids (glycosylation and proteolytic modification).