Ribosomes

Question 1

What are polyribosomes?

Answer 1

Two or more ribosomes that act together to translate mRNA instructions.

Question 2

What kind of proteins do the RER-bound ribosomes produce?

Answer 2

1. Trafficking membrane proteins
2. Secretory proteins and lysosomal proteins.

Proteins that are exported.

Question 3

What kind of proteins do the free cytosolic ribosomes produce?

Answer 3

1. Nuclear proteins
2. Mitochondrial proteins
3. Peroxismal proteins
4. Cytosolic proteins.
5. Cytoskeletal proteins.

• Proteins used inside the cell itself.

Question 4

What is the main function of RER?

Answer 4

Protein synthesis. It contains SRP receptors and translocons.

Question 5

What are the main functions of SER?

Answer 5

1. Lipid synthesis
2. Storage of calcium
3. Detoxification of xenobiotics.

No ribosomes. No SRP receptors.

Question 6

What are dictyosomes?

Answer 6

Flat membrane-bound cavities that together form the Golgi apparatus. Here proteins are stored, modified, sorted and packed into vesicles.

Question 7

What’s the difference between the two poles of the dictyosomes?

Answer 7

Cis: Convex, 5nm thick, ER like membrane proteins.

Trans: Concave, 7.5 nm thick, cell membrane-like proteins, many sugar residues bound to inner aspect of membrane.

Question 8

How do the dictyosomes work?

Answer 8

1. Vesicles arrive at the cis-face of the dictyosome.
2. While transferred through the dictyosome to the trans face the proteins undergo modifications.
3. After the trans face, the proteins are transferred to the trans-Golgi network where they are sorted to different vesicles.

Question 9

What are the three types of vesicles released by the dictyosomes?

Answer 9

1. Small vesicles (supplying new membrane fragments to the cell membrane.
2. Large vesicles (Containing condensed secretory material for regulated exocytosis)
3. Hydrolase vesicles (Containing digestive enzymes) - Precursors of lysosomes