Golgi Apparatus

Question 1

How do proteins/lipids enter the Golgi network?

Answer 1

Packaged into vesicles coated with protein COPII which merge to form a vesicular tubular cluster, which then travels along the microtubules to merge with the cis-Golgi network

Question 2

How do membrane proteins ensure that they reach the membrane?

Answer 2

Have specific exit signals which can be di-acidic (2Glu, 2Asp) or di-hydrophobic (2*Met)

Question 3

How are resident ER proteins retrieved?

Answer 3

• Via ER retrieval motif KDEL

- Receptors bind to this and form COPI coat to retrieve proteins

Question 4

What is the structure of the Golgi apparatus?

Answer 4

• Made from lipid sacks called cisternae

- Proteins/lipids join as the cis-face and leave at the trans-face

Question 5

What does the N-linked glycosylation of a protein depend on?

Answer 5

Composition of the protein, its destination, how fast it’s going and what enzymes are present -> determines protein fate

Question 6

How does N-linked glycolisation occur?

Answer 6

Via the addition and removal of sugars via glycosiletransferases and glycosidases

Question 7

What is O-linked glycolisation and when is it used?

Answer 7

• Linked to serine/threonine molecules
• Addition of one sugar at a time and only a few oligosaccharides
• Common in many cytoplasmic/nuclear proteins and transcription factors
• Present in eukaryotes, bacteria and archea

Question 8

Describe the process of sphingomyelin and glycolipid synthesis

Answer 8

Ceramide (sphingosine+fatty acid) can have added a phosphorylcholine group to form sphingomyelin or sugar residues to form glycolipids

Question 9

Name 5 other Golgi-mediated modifications

Answer 9

• Sulfation of tyrosine residues
• Phosphorylation
• Proteolytic processing
• Palmitoylation
• Oligomerisation
  (Happen at different places in the Golgi apparatus)

Question 10

What is the difference between the vesicular transport model and the cisternal maturation model?

Answer 10

vesicular transport - molecules all move in small vesicles, however energetically unfeasible and some proteins are too big
cisternal maturation - Entire stack moves forward, only Golgi enzymes are transported back by vesicles

Question 11

How does the trans-Golgi network ensure that proteins are delivered to the correct location?

Answer 11

• Protein markers attached

- One of the most common being mannose-6-phosphate which signals for lysosome

Question 12

How is mannose-6-phosphate produced?

Answer 12

Phosphorylation by UDP addition and loss of N-acetylglucosamine

Question 13

What is the difference between constituive and regulated secretory pathways?

Answer 13

Constituive is unregulated

Regulated is controlled by various proteins and molecules such as neurotransmitters and hormones