Exam 3 - Andreas Slides

Question 1

What are the three types of cytoskeletal fibers?

Answer 1

1. Microtubule (tublin)
2. Actin filament
3. Intermediate filament (only in animal cells, 6 different types of proteins)
   - Mutations of microtubules and actin basically will kill you because they are so important for life. - Fibers made of polymerized protein.

Question 2

What do actins do?

Answer 2

1. Bind nucleotides (ATP) 2. Forms tight helical filaments (F-actin) from globular domains (G-actin) 3. Polar polymer (pointed and barbed end) Like a pine tree 4. Essential for all Eucaryotic cells (Cell motility/cytokinesis/muscle contraction) 5. The most abundant protein in the world

Question 3

What do microtubules do?

Answer 3

1. GTP binding site 2. Forms hollow tubes -> alpha-beta-tubulin dimer 3. Polar polymer (plus and minus end) 4. Essential for all Eucaryotic cells (mitosis/trafficking between cell center and periphery) 5. Similar proteins in some Bacteria (EG. FtsZ)

Question 4

What do Intermediate Filaments do?

Answer 4

1. No nucleotide binding site 2. Six different classes -> bundles of alpha helical coiled-coil proteins. 3. Filaments have no polarity 4. Metazoan (animal) cells (cell structure and shape/stability) 5. Some similar structures found in bacteria 6. Involved in a variety of diseases (mutations all over the place)

Question 5

Describe Myosins (in Actin)

Answer 5

Directionality: Mostly barbed end Speed: 0.5-1micrometer/sec Force: 1-5 pN Location: Muscle, cytoplasm, cell periphery

Question 6

Describe Dyneins (In Microtubules)

Answer 6

Directionality: Minus-end Speed: Unknown Force: 1-5 pN Location: Axonemes (flagella cilias) cytoplasm, spindle, axons

Question 7

Describe Kinesins (In microtubules)

Answer 7

Directionality: Most plus-end (N-term) some minus-end (C-term) Speed: 0.2-2 um/s Force: 1-5 pN Location: Axons, spindles, cytoplasm

Question 8

Why is the force the same across the molecular motors?

Answer 8

They all consume the same energy source = ATP

Question 9

Which cytoskeletal system does NOT support molecular motors, and why?

Answer 9

Intermediate Filaments because they are non-polar (no directionality)

Question 10

Why would you want a protein to sever the middle of a MT?

Answer 10

1. Katanin frees up MTs that can be moved to cilia and axons. 2. It also helps to turn over MTs rapidly.

Question 11

Why would you want a protein to remove the GTP cap of a MT?

Answer 11

Microtubules need to shrink, e.g. during chromosome segregation in mitosis. (EG. MCAK

Question 12

What is XMAP215?

Answer 12

A stabilizing (+) end binding protein that catalyzes the addition of multiple individual tubulin subunits.

Question 13

What is CLIP170?

Answer 13

A MAP that both stabilizes (+) TIPs and binds to endocytic vesicles.

Question 14

The (+) end of a microtubule is?

Answer 14

More dynamic than the (-) end.

Question 15

What is MTOC?

Answer 15

Microtubule organizing center

Question 16

There are more MTs during mitosis but they are shorter. Why?

Answer 16

Less stabilizing MAPs and more gamma-TuRC

Question 17

(+) end cap regulates ___________.

Answer 17

stability of MT

Question 18

Most stable conformation of protofilaments of GTP tubulin is ______.

Answer 18

Straight

Question 19

Most stable conformation of protofilaments of GDP tubulin is ______.

Answer 19

Curved

Question 20

What happens when the GTP cap is lost?

Answer 20

Protofilaments curl outward leading to individual curved protofilaments breaking off the microtubule and depolymerizing.

Question 21

What is MAPs?

Answer 21

Microtubule Associated Protein(s)

Question 22

What does Human Tau40 do?

Answer 22

1. Non-motor MAP 2. Highly flexible/no secondary structure 3. Effective modulator of microtubule dynamics

Question 23

MAPs can do what to MTs?

Answer 23

1. Destabilize 2. Speed up microtubule turnover

Question 24

What does MCAK (GAP) do?

Answer 24

Removes GTP cap from growing microtubule to cause disassociation of tubulin subunits = shortening.

Question 25

What does Katanin do?

Answer 25

Severs intact MT which helps with MT turnover and transfer of MTs.

Question 26

What does colchicine (drug) do?

Answer 26

Sequesters dimers. - Sometimes subunits of MT are free to polymerize, but the drug stops (binds with) subunits to prevent polymerization.

Question 27

How do (+) TIPs stabilize the (+) tip?

Answer 27

+TIP proteins bind to the polymerizing + end of microtubule.

Question 28

Describe the MT polarity in Fibroblast, Epithelial cells, and neurons.

Answer 28

Question 29

Transport from the ER to the Golgi is what? (Directionality)

Answer 29

Retrograde (+ end to - end)

Question 30

Transport from the Golgi to the Plasma mebrane is what? (Directionality)

Answer 30

Anterograde (- end to + end)

Question 31

What is the Pulse-chase experiment?

Answer 31

Things beginning in the ER travel to Golgi, then to Plasma membrane. - Temperature sensitive VSVG mutant begins to traffic at permissive temp.

Question 32

Briefly describe Kinesins and its directionality.

Answer 32

1. MT-based Motor Protein 2. Plus AND minus-end directed motors (BUT mostly plus end)

Question 33

Briefly describe Dyneins and its directionality.

Answer 33

1. MT-based motor protein. 2. Minus-end directed motors

Question 34

How are cargo loaded onto motors?

Answer 34

Tail domain binds cargo via adaptor protein.

Question 35

Plus-end Kinesin starts at ______ and minus-end starts at \_\_\_\_\_\_.

Answer 35

N-terminus, C-terminus

Question 36

Retrograde transport is towards _______ while Anterograde is towards \_\_\_\_\_\_\_\_.

Answer 36

Cell body, synapse

Question 37

What is the driving force of dimerization in Kinesin-1 (a homodimer)?

Answer 37

Hydrophobic interactions, alpha-helical coiled-coil formation, and leucine zipper.

Question 38

Which regions in a kinesin motor domain are controlling microtubule-binding?

Answer 38

The ATP-binding site (part of switch-1), The switch-II region, and the neck-linker region.

Question 39

What are actin stressfibers?

Answer 39

Contractile bundles of actin filaments and myosin that are anchored to focal adhesions at the plasma membrane and function in cell adhesion.

Question 40

What are Hemidesmosomes?

Answer 40

Anchoring junctions: form rivet-like links between cytoskeleton and extracellular matrix components such as the basal laminae that underlie epithelia. Like desmosomes, they tie to intermediate filaments in the cytoplasm, but in their transmembrane anchors are integrins rather than cadherins.

Question 41

What are desmosomes?

Answer 41

Anchoring function: Rivets through the plasma membrane of adjacent cells. Cadherin molecules form the actual anchor by attaching to the cytoplasmic plaque.

Question 42

What are adherens junctions?

Answer 42

Anchoring Junction: Share the characteristic of anchoring cells through their cytoplasmic actin filaments. Composed of cadherins and integrins.

Question 43

What do cadherins anchor to?

Answer 43

Other cells

Question 44

What do integrins anchor to?

Answer 44

Extracellular matrix

Question 45

What do tight junctions do?

Answer 45

Act as barriers that regulate the movement of water and solutes between epithelial layers. Classified as a paracellular barrier: not having directional discrimination (movement is largely dependent upon solute size and chare)

Question 46

Why are tight junctions AKA occluding junctions or zonula occludens?

Answer 46

This junctional complex is only present in vertebrates. (Septate junctions occur in invertebrates)

Question 47

What are communicating (GAP) junctions?

Answer 47

Allow for direct chemical communication between adjacent cellular cytoplasm through diffusion without contact of the extracellular fluid.

Question 48

What are connexin proteins?

Answer 48

A protein found in gap junctions and six of them interact to form a cylinder with a pore in the center. Goes across the cell membrane and interacts with an adjacent cell connexon (6 connexins) to form a gap junction channel.