Class 13 - Lysosomes and Proteasome (GOOD)

Question 1

M6P

Answer 1

Marker which allows recognition and selection of lysosomal hydrolases to be transported to lysosomes

Signal added in cis Golgi network to N-linked oligosaccharides.

Question 2

M6P receptor protein

Answer 2

Transmembrane protein found in the TGN which recognize M6P groups, bind to lysosomal hydrolases, and bind to adaptor proteins assembling clathrin coats.

Uses signals at cytoplasmic tail to guide direction and allow recognition at TGN or endosome.

Binds at high pH and releases at low pH of endosome lumen

Question 3

Lysosomal storage diseases

Answer 3

Genetic defects that affect one or more lysosomal hydrolase (e.g. Hurler’s disease) which are excreted because of mis-sorting.

Result in accumulation of undigested substrates in lysosomes. Typically affect nervous system.

In worst form (I-cell disease) lysosomes don’t receive M6P tags —> inclusions form in the cell, impacting organs, skeleton, and mental development.

Question 4

Lysosome

Answer 4

Membrane enclosed, highly glycosylated membrane proteins. All eukaryotic cell.

Hydrolytic enzymes for digesting
macromolecules. Site for degradation and recycling of proteins, nucleic acids, and lipids (autophagy).

Has H+ pumping into it to keep pH low, also providing H+ gradient across membrane.

Final products put in cytosol and reused or excreted.

Heterogenous - Morphologically diverse

Question 5

Acid hydrolase

Answer 5

Hydrolytic enzymes in lysosomes which break down molecules.

pH in lysosome kept low (acidic) so acid hydrolase can function.

Question 6

Vacuole

Answer 6

Large fluid filled vesicles found in plants and fungi (equivalent to animal cell lysosome).

Store nutrients and waste, degradation, increase cell size, control turgor pressure (help balance pH).

Question 7

Autophagy

Answer 7

4th pathway - “Self-eating.” Used to digest cytosol, worn-out organelles, and microbes that invade the cytosol.

Cytoplasm portion engulfed into membraned autophagosome which fuses with a lysosome to be degraded.

Roles: Helps restructure differentiating cells by removing unwanted cellular contents, recycle existing molecules, degrade bacteria/viruses and damaged molecules.

Question 8

Autophagosome

Answer 8

Membrane structure during autophagy which engulfs a portion of the cytosol then fuses with a lysosome to be degraded.

Question 9

Nonselective autophagy

Answer 9

Bulk portion of cytoplasm sequestered into autophagosomes. Does not require ubiquitin tag.

Question 10

Selective autophagy

Answer 10

Autoohagosomes tightly enclose specific cargo and mostly exclude surrounding cytosol. Requires ubiquitin tag.

Question 11

Proteasome

Answer 11

Abundant proteins dispersed throughout cytosol and nucleus (if protein is in ER, it’s translocated to cytosol).

Central hollow cylinder with protein subunits. Proteins threaded through using ATP and exposed to proteases lining proteasome core.

Question 12

Ubiquitin

Answer 12

Act as a mark for cargo destined for degradation via selective autophagy.

Attached as a polyubiquitin chain on misfolded proteins. Delivers proteasome.

Question 13

Default pathway

Answer 13

To the cell surface.

Also called the nonselective constitutive secretory pathways.

Question 14

Macropinocytosis

Answer 14

2nd pathway - Nonspecific uptake of fluids, membranes, and particles attached to plasma membrane.

Question 15

Phagocytosis

Answer 15

3rd pathway - Found in phagocytic cells and involved engulfment (phagocytosis) of large particles and microorganisms to form phagosomes.

Question 16

Endocytosis

Answer 16

1st pathway- The taking in of matter by a cell by invagination or its membrane to form a vacuole.

Also used to regulate location and trafficking of macromolecules.

Question 17

Autophagy and nutrient availability

Answer 17

Starvation-induced nonselective autophagy is important because it allows acquisition of amino acids to sustain critical cellular functions until steady food source is established.