Lecture 21

Question 1

What is a tonoplast?

Answer 1

vacuolar membrane containing active transport systems allowing ions and molecule transport

Question 2

Microtubules (MT)

Answer 2

• largest cytoskeletal element

- polymer of 2 diff proteins: a-tubulin, B-tubulin

Question 3

What are associated proteins (MAPS)?

Answer 3

several diff proteins binding to MTs

• modulate assembly, function
• mediate interactions w/ other cellular structures

Question 4

Plant Vacuole Functions

Answer 4

1. intracellular digestion comparable to lysosomes
2. mechanical support, turgor pressure
   - gives rigidity to plant-supports soft tissues
   - stretches cell wall during growth
3. storage
   - solutes and macromolecules
   - chemical storage (toxic compounds as well)

Question 5

Microtubules structure

Answer 5

• a/B heterodimers form long protofilaments
• 13 protofilaments from longitudinal array creating structural polarity
• heterodimers are aligned in the same direction creating structural polarity

Question 6

What are microfilaments?

Answer 6

a hollow tube formed from tubulin dimers

Question 7

Cytoskeleton functions

Answer 7

1) structural support
2) spatial organization w/in cell
3) intracellular transport
4) contractility and mobility

Question 8

What is a cytoskeleton made out of?

Answer 8

dynamic network of interconnected filaments and tubes- extended throughout cytosol of eukaryotes

Question 9

What are microtubules?

Answer 9

double helix of actin monomers

Question 10

MTs ends

Answer 10

fast-growing: plus end

slow-growing: minus-end

Question 11

Cytoskeleton components

Answer 11

• microfilaments
• microtubules
• intermediate filaments

Question 12

Microtubules assembly and disassembly

Answer 12

microtubules undergo dynamic assembly and disassembly

• shrinkage occurs very rapidly at + end - termed catastrophe
• formation of MTs is regulated/ controlled

Question 13

What are intermediate filaments?

Answer 13

strong fiber composed of intermediate filament protein subunits

Question 14

What do APs help do?**

Answer 14

form endocytic vesicles from plasma membrane to endosomes/lysosomes

Question 15

What are the types of microtubules?

Answer 15

1. Axonemal MT: organized stable part of structures involved in cell movement
2. Cytoplasmic MT: loosely organized very dynamic in cytosol

Question 16

What are the 2 classes of MAPS?

Answer 16

1. Non-motor MAPs
   - control MT organization in cytosol
   - defective Tau protein
2. Motor MAPs
   - kinesin (+) and dynein (-)
   - ATP for generated force
   - move material along MT track
   - generated sliding force between MTs

Question 17

Plant vacuoles

Answer 17

• fluid-filled membrane-bound
• take up 90% of cells volume
• involved in regulation of toxic ions, regulation of cell turgor, storage of amino acids, sugars and CO2 in malate form

Question 18

What is the 2nd function of lysosomes?**

Answer 18

2. Degradation of internalized material
   - recycling of plasma membrane components like receptors and extracellular material
   - destroy pathogens like bacteria and viruses- only in phagocytic cells

Question 19

What is the AP complex?**

Answer 19

• Cathrin Adaptor Proteins
• coated vesicles move from TGN to other vesicles
• e.g. lysosomes, endosomes

Question 20

What is dynamic instability?

Answer 20

rapid turnover of most MTs in vivo, half-life in minutes w/in cells

Question 21

What is the first function of lysosomes?*****

Answer 21

1. Autophagy: normal disassembly of unnecessary/ dysfunctional cellular components-organelle turnover
   - membrane derived from ER engulfs target organelle: autophagosome formation
   - lysosome fuses w/ ER-derived autophagic vesicle: autolysosome formation
   - the content of autolysosome is enzymatically digested and released (exocytosis)
   Autophagosome formation → Lysosome recruitment → Autolysosome → Digestion
   and release