Cytoskeleton

Question 1

What are the 3 main classes of cytoskeletal structures?

Answer 1

Microtubules, actin filaments, and intermediate filaments

Question 2

What are microtubules’ monomeres?

Answer 2

alpha and beta tubulins.

Question 3

Do microtubules have a polarity?

Answer 3

Yes

Question 4

Are microtubules dynamic or stable?

Answer 4

In axonemes they are more stable, in the cytoplasm they are more dynamic.

Question 5

What is the function of microtubules?

Answer 5

Maintains the structure of the cell, as a pathway for molecule transport, and formation of cilia and flagellum.

Question 5

What protein is tubulin polymerization done by?

Answer 5

Microtubule organizing center (MTOC).

Question 6

What is the molecular weight of tubulins?

Answer 6

Approx. 50kDa

Question 7

What molecules affect the formation of microtubules? Name 3!

Answer 7

Calcium, magnesium, and MAP (microtubule associated proteins).

Question 8

What is the structure of the MTOC?

Answer 8

Short microtubulin filaments that help

Question 9

True or False?

The centriole of centrosomes divide into 2 pairs during DNA replication to prepare for mitosis.

Answer 9

True

Question 10

What motor proteins are used for proteins transport?

Answer 10

Dinein and kinesin, dinein is for retrograde, kinesin is for anterograde

Question 11

What monomers make up the actin filament?

Answer 11

G-actin forms 2 F-actin filaments.

Question 12

What molecule supports actin polymerization from a pool of G-actins?

Answer 12

Formin.

Question 13

What molecule complex triggers actin branching?

Answer 13

The Arp2/3 complex triggers the branching of actins.

Question 14

What is the flow of microtubulin addition?

Answer 14

Microtubulins are known for having their polarities, with the positive (+) aspect as where tubulins are added.

In tubulin dense cytoplasmic regions (free-floating tubulins), these GTP tubulins are attached to the microtubules and done in such a fashion that the hydrolysis of the GTP is slower than the addition of a newer GTP tubulin.

In conditions where free floating tubulin GTPs aren’t present, hydrolysis is done which creates higher levels of tubulin GDPs which are known to be unstable and proje to depolymerization.

Question 15

What is special about the polymerization of actin filaments in relation to their polarity?

Answer 15

Regulatory molecules like profilin induce the addition of G-actin onto the positive (+) aspect of the actin filaments while cofilin induces the removal of G-actin form the negative (-) aspect of the actin filaments.

This mechanism enables treadmilling which makes molecules easily transferrable from one side of the polar actin to the other.

Question 16

What is the part of the cell occupied by actin microfilaments?

Answer 16

Cortex.

Question 17

What structures are formed by the microfilaments for movement of cells?

Answer 17

Lamellapodia and filopodia.

Question 18

What structures are formed by the microfilaments for structural support of the cells?

Answer 18

Stress fibers.

Question 19

What molecule transports molecules throughout actin microfilaments

Answer 19

Myosin, typically from the negative to positive polarity, only myosin VI is known to go from positive to negative remember pos (3 letters) + neg (3 letters) = 6 letters

Question 20

What is the function of actin microfilaments?

Answer 20

1. Cytoplasmic flow
2. Contracting of the cells
3. Maintains the shape of the cell
4. Cell division

Question 21

Which myosin control cytokinesis?

Answer 21

Myosin 2 (remember: 2 cells)

Question 22

Which myosin controls endocytosis?

Answer 22

Myosin 1 (remember: 1 item for 1 cell)

Question 23

What protein encloses the actin filament?

Answer 23

CapZ proteins.

Question 24

What protein **cuts** and **encloses** the actin filament?

Answer 24

Spectrin.

Question 25

What protein enables **parallelization** of the actin filaments?

Answer 25

Fimbrin, alpha actinin, and villin.

Question 26

Are intermediate filaments stable or dynamic?

Answer 26

Stable

Question 27

What are the 4 most significant intermediate filaments?

Answer 27

Vimentin, lamin, keratin, neurofilament.

Question 28

What does lamin do?

Answer 28

Stabilizes the nuclear membrane by creating the nuclear lamina.

Question 29

What structures are formed by keratins?

Answer 29

They form tonofibrils that connect cell junctions and cellular protection (i.e. epidermis).

Question 30

What are the 4 types of neurofilaments?

Answer 30

alpha internexin (embryonic neurons), NF-H, NF-M, & NF-L

Question 31

Where can desmin be located?

Answer 31

Desmin can be found in myocytes.

Question 32

What are acidic cytokeratin associated with?

Answer 32

Class I intermediate filaments that are associated with skin boils.

Question 33

Where can GFAP proteins be located?

Answer 33

Astrocytes

Question 34

Mention the class III intermediate filaments!

Answer 34

Desmin, sinemin, GFAP, peripherin, and vimentin.

Question 35

What are the class VI intermediate filaments?

Answer 35

The nestins that exist in neurons.

Question 36

What disease is associated with GFAP?

Answer 36

Alexander's disease, marked by an accumulation of Rosenthal fibers indicates a mutation in the GFAP gene, influencing the caspase 3 activity, hence causing the hyperapoptosis of astrocytes.