Endocytosis, autophagy, cytoskeleton

Question 1

Plant vacuoles

Answer 1

• Plant vacuoles are fluid - filled, membrane
  bound
• They can take up ~90% of the cells volume
• Vacuoles are involved in the regulation
  of cytoplasmic pH, sequestration of
  toxic ions, regulation of cell turgor
  (rigidity), storage of amino acids,
  sugars, and CO2 in the form of malate.

Question 2

Tonoplast

Answer 2

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

Question 3

Function of plant

Answer 3

1. Intracellular digestion comparable to lysosomes—slightl low pH (5.0), acid hydrolases.
2. Mechanical support via 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 as pigments like anthocyanin)

Question 4

Cytoskeleton

Answer 4

• Dynamic network of interconnected filaments and tubes that extends throughout the cytosol (and some organelles) of eukaryotes

Question 5

Function of the cytoskeleton

Answer 5

1) structural support
2) spatial organization within cell
3) intracellular transport
4) contractility and motility.

Question 6

Components of the cytoskeleton

Answer 6

• Microfilament
• Microtubules
• Intermediate filaments

Question 7

Microfilament

Answer 7

• Actin
  -7-9nm

Question 8

Intermediate filaments

Answer 8

-Various
-10nm

Question 9

Microtubules

Answer 9

• Largest cytoskeletal element (25 nm diameter).
• Polymer of two different proteins (monomers): α-tubulin and β-tubulin.

2 major types:
-Axonemal MT
-Cytoplasmic MT

Question 10

Axonemal

Answer 10

-Highly organized, stable
Part of structures (axoneme) involved in cell movement (e.g cilia, flagella)

Question 11

Cytoplasmic MT

Answer 11

• Loosely organized, very dynamic
• Located in cytosol

Question 12

Microtubules Structure

Answer 12

• α/β heterodimers form long protofilaments
• 13 protofilaments form longitudinal array creating
  an hollow cylinder

Question 13

Heterodimers

Answer 13

• Heterodimers are aligned in the same direction
  (head to tail) creating structural polarity.

Question 14

Structural polarity of microtubules

Answer 14

• MTs have a fast-growing ‘plus’ end and a slow- growing ‘minus’ end.

-This structural polarity is very important for MT
growth and the direction of movement of material
along MT

Question 15

Microtubules Assembly/Disassembly

Answer 15

• Microtubules undergo dynamic assembly and disassembly:
• Dynamic instability—rapid turnover of most MTs in vivo. In fact, half-life in
  minutes within cells.

-Shrinkage can occur very rapidly at the ‘plus’ end—termed ‘catastrophe’.

• Formation of MTs is regulated /
  controlled.

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

Question 16

Microtubule-Associated Proteins (MAPs)

Answer 16

-Several different proteins that bind MTs.

-Modulate assembly, function

-Mediate interactions with other cellular structures (e.g vesicles/organelles)

-Stabilize MTs or stimulate assembly.

Question 17

Two classes of MAPs

Answer 17

1. Non - Motor maps
2. Motor maps

Question 18

Non-Motor MAPs:

Answer 18

• Control MT organization in cytosol (e.g. Tau protein in neurons).
• Defective Tau protein → neurofibrillary tangles → Alzheimer’s disease

Question 19

Motor maps

Answer 19

• Two main types—kinesin and dynein.
• Use ATP to generate force.
• Can move material along MT track.
• Can generate sliding force between MTs. (important during mitosis and chromosome separation)