Lecture 21

Question 1

What directs vesicles to other part of the cell in late biosynthetic secretory pathway

Answer 1

Trans Golgi to endosomes
Trans Golgi to lysosomes
Plasma Membrane to endosomes

Question 2

What is the two-layer coat made of?
what are each of their functions

Answer 2

Clathrin: outer layer, vesicle formation and structure

AP complex (Clathrin adaptor protein complex): inner layer, 3 different complexes, select cargo, different trafficking routes

Question 3

Does the AP/Clathrin-coated vesicles move from the TGN

Answer 3

Yes, they move to other compartments (ex. lysosomes, endosomes, plant vacuoles)

Question 4

What is another function of AP/Clathrin-coated vesicles

Answer 4

they form endocytic vesicles to move material from the plasma membrane/extracellular membrane into the cell

Question 5

Describe the autophagy function of a lysosome

Answer 5

Disassembly of unnecessary/dysfunctional cellular components (organelle turnover)

Isolation membrane (initiation) from the ER engulf target organelle (vesicle elongation and maturation) and form an autophagosome (autophagic vesicle)

Lysosome fuses with autophagic vesicle to form a autolysosome (docking and fusion)

content of autolysosome is enzymatically digested and released (exocytosis, vesicle breakdown and degradation)

Question 6

Describe the degradation of internalized material function of a lysosome

Answer 6

plasma membrane components (receptors and extracellular material) are recycled

Destruction of pathogens like bacteria and viruses (internalized by phagocytic cell, degraded by lysosome, killed by enzyme and released outside of the cell)

Question 7

What are plant vacuoles

Answer 7

Large organelles that are filled with fluid, are membrane-bound and help to maintain structure

takes up 90% up the cell’s volume

Question 8

What activities are plant vacuoles involved in

Answer 8

Regulation of cytoplasmic pH
sequestration of toxic ions
regulation of cell rigidity
storage of amino acids, sugars and CO2 in malate form

Question 9

What is a tonoplast (associated with plant vacuole)

Answer 9

Vacuolar membrane that contains active support systems that allows for ion and molecule transport

Question 10

What are the functions of plant vacuoles

Answer 10

1) Intracellular digestion: comparable to lysosomes, pH = 5.0, acid hydrolases enzyme

2) Mechanical support, turgor pressure: gives rigidity to plant (supports soft tissue), stretches cell wall during growth

3) Storage: solutes and macromolecules, chemical storage (toxic compound and pigments like anthocyanin)

Question 11

What is the cytoskeleton

Answer 11

dynamic network of interconnected filaments and tubes that extends throughout cytosol of eukaryotes

Question 12

What are the functions of the cytoskeleton

Answer 12

1) Structural support
2) Spatial organization in the cell
3) Intracellular transport
4) Contractility and motility

Question 13

What are the three components of the cytoskeleton

Answer 13

Microfilaments
Microtubules
Intermediate filaments

Question 14

Describe microtubules (structure and different types)

Answer 14

Largest component of the cytoskeleton (25nm)
Polymer made of 2 proteins (monomers): alpha-tubulin and beta-tubulin

Axonemal MT: Highly organized, stable, part of structure involved with movement

Cytoplasmic MT: Loosely organized, very dynamic, located in the cytosol

Question 15

Describe the structure of microtubules (again)

Answer 15

alpha/beta heterodimers form long protofilaments (13 form longitudinal array, a hollow cylinder)

Structural polarity created (fast-growing “+” end and slow-growing “-“ end)
Important for growth and direction of movement of material along MT

Question 16

Describe the assembly/disassembly of microtubules

Answer 16

Very dynamic

dynamic instability (rapid turnover, half-life is only a few minutes)

Shrinkage occurs rapidly at the “+” end

Formation of MTs are regulated/controlled

Microtubule-organizing center (MTOC) is the central site of MT assembly

Question 17

What are microtubule-associated proteins (MAPs)

Answer 17

Different proteins that bind to MTs
Modulate assembly, function
Mediates interactions with other cellular structures
Stabilize MTs or stimulate assembly

Question 18

What are the 2 classes of MAPs? What are their functions?

Answer 18

Non-Motor MAPS: Control MT organization in the cytosol, stabilize MTs or stimulate assembly
defective tau proteins = neurofibrillary tangles = Alzheimer’s disease,

Motor MAPs: 2 types (kinesin and dynein) uses ATP to generate force, moves material along MT track, generates sliding force between MTs
Kinesin - plus end directed
Dynein - minus end directed