Trafficking

Question 1

What is meant by cellular trafficking?

Answer 1

Movement of molecules from synthesis-and-packaging locations in the Golgi body to ‘release’ locations on the inside of the plasma membrane in the form of vesicles, termed membrane vesicles (MVs).

Question 2

What happens to proteins made on free ribosomes?

Answer 2

Enter mitochondria or nucleus (contain specific signal sequences)

Question 3

What happens after vesicles containing protein reach Golgi?

Answer 3

Pass through cis, median and trans region of golgi, and enter transgolgi network where they are targeted to correct location

Question 4

What 2 things can happens as vesicle with protein approaches membrane?

Answer 4

Fuse at plasma membrane and add new protein to membrane

Allow vesicle contents to be released into extracellular medium

Question 5

What is difference between constitutive and regulated secretion?

Answer 5

Constitutive: proteins secreted /integrated into membrane as soon as they’re synthesised and processed

Regulated: proteins synthesised, processed and stored in vesicles before being released when signal received.

Question 6

What is receptor mediated endocytosis?

Answer 6

Macromolecules enter cell by binding receptors on plasma membrane

Question 7

How does receptor mediated endocytosis occur?

Answer 7

Receptors in clatharin coated pits

These pits form endocytic vesicles which become endosomes

Lysosomes hydrolyse endocytosed contents

Question 8

What is transcytosis?

Answer 8

Compounds taken up as vesicle on one side and cross cell membrane, released by exocytosis on another side

Non selective uptake

Question 9

What cells frequently undergo transcytosis?

Answer 9

Endothelial cells (epithelia)

Question 10

What are signal sequences, where are they present?

Answer 10

Sequence present at N terminus of newly synthesised proteins that are destined towards secretory pathway.

Question 11

What does the presence of a signal sequence trigger?

Answer 11

Signal sequences prompt cell to translocate protein e.g. to cell membrane for secretion

Question 12

What are the three stages vesicles produced from golgi body go through ?

Answer 12

Vesicles are released into the cytoplasm in a process called budding.

Vesicles are then moved towards their destination by motor proteins.

Once the vesicle arrives at its destination (membrane or lysosome) it joins with the bi-lipid layer in a process called fusion, and then releases its contents.

Question 13

What is budding?

Answer 13

Release of a vesicle from the golgi

Question 14

What is needed for effective budding?

Answer 14

Coating proteins

Question 15

What proteins move vesicles as cargo along the cytoskeleton?

Answer 15

Motor proteins

Question 16

What proteins cause the vesicle to merge with the membrane?

Answer 16

Docking proteins (membrane) interact with RAB/G-proteins (vesicle)

Then SNARE pulls closer

Question 17

What is the function of receptor mediated endocytosis?

Answer 17

Cells absorb metabolites, hormones, proteins by the inward budding of the plasma membrane (invagination)

Question 18

What are examples of macromolecules transported by transcytosis?

Answer 18

IgA, transferrin, insulin

Question 19

What is an example of a substance released by exocytosis?

Answer 19

Insulin granules from beta cells

Question 20

The site of translation for most secreted proteins

Answer 20

Rough endoplasmic reticulum

Question 21

The site of degradation for most endocytosed plasma membrane proteins

Answer 21

Lysosomes

Question 22

The structure(s) from which secretory vesicles typically bud off prior to fusion with the plasma membrane

Answer 22

Trans-Golgi network