Polvi lec #12

Question 1

What are the two roles of lysosomes?

Answer 1

Breakdown of material
and organelle turnover

Question 2

How do lysosomes break down materials?

Answer 2

The material gets brought into the cell by endocytosis and then gets degraded after being transferred to lysosomes

Question 3

How do lysosomes do organelle turnover (autophagy)?

Answer 3

The organelle is surrounded by a double membrane structure called an autophagasome this fuses with a lysome and the outside membrane adds to lysome and inside membrane gets degraded, the final product is called an autolysosome

Question 4

What happens to autolysomes?

Answer 4

can be shipped out or retained

Question 5

What happens when we have a lysosomal storage disorder?

Answer 5

We have deficient lysosomal enzymes and that leads to an accumulation of undegraded materials- this leads to diseases

Question 6

What do clathrin coated vesicles do?

Answer 6

move materials from trans golgi to endosomes, lysosomes, plant vacuoles and outside the cell

Question 7

How does the sorting and transport of lysosomal enzymes work?

Answer 7

soluble lysosomal enzymes are recognized by enzymes that add phosphate groups to the mannose of N-linked glycochains, these become phosphorylated mannose which act as a sorting signal, directing proteins to the lysosome

Question 8

Explain step by step how lysosomal enzymes get sorted and transported to lysosomes?

Answer 8

1. Mannose residues of lysosomal enzy,es are phosphorylated in the golgi
2. phosphorylated lysosomal enzymes are incorporated into a clathrin coated vesicle in the trans golgi
3. Vesicle buds away from trans golgi the clathrin coat disassembles and the lysosome enzyme are delivered to a sorting endosome and then onto a lysosome, recpetors get cycles back to trans golgi
4. Mannose phosphate receptors found in the plasma membrane capture lysosomal enzymes that are secreted into the extracellular space and return these enzymes to the lysosome

Question 9

How is the clathrin coated vesilce formed?

Answer 9

The Mannose phosphate receptor recognizes the manoos phosphate signal on enzymes, the GGA adaptor connects the receprot and the clathrin coat, arf1-GPR also binds to GGA adaptor and formes the budding clathrin coated vesicle

Question 10

Do cisternae golgi continually move to the TGN? What does this imply?

Answer 10

yes, this implies that constitutive secretion is the default

Question 11

What are the two types of endocytosis?

Answer 11

Bulk-phase endocytosis - takes up any fluids of mlcls in cell
receptor mediated endocytosis- is clathrin mediated and specific molecules bind to receptors on the extracellular surface of the plasma membrane

Question 12

How does receptor mediated endocytosis work?

Answer 12

AP2 complex links the tails of the plasma mebrane with clathrin and clathrin forms triskelions around incoming cargo, dynamin subunits go on budding vesicle, form a ring, and then go through hydrolysis and cleaves the clathrin coated vesicle into the cell and dynamin disassembles

Question 13

What two pathways can endocytosis take?

Answer 13

recycling pathway- where housekeeping receptors mediate uptake of materials that will be used by the cell
receptors are first transported to an early endosome and are sorted, then the receptor and material disassociate due to acidic ph, then receptors get concentrated and packaged off to the cells surface to be used again
Degradation pathway- signalling receptors here bind ligands that affect cellular activities, first receptors get put into early endosomes and then that matures into late endosome and the late endosome fuses with a lysosome for receptor degradation which stops cell from being further excited