Cell Bio 2

Front 1

The cytoskeleton describes a network of protein filaments in the cytoplasm of cells. What are the diameters of the filaments: microtubules, filaments and intermediate filaments?

Back 1

Microtubules: 25 nm

Microfilaments: 7-9nm

Intermediate filaments: 10nm

Front 2

Microfilaments are composed of the protein _____________ whereas microtubules are composed of the protein ________________.

Back 2

Actin, tubulin.

Front 3

Name at least 4 of the general functions of the cytoskeleton.

Back 3

Functions of the cytoskeleton include: organelle/protein trafficking, cilia/flagella, mitosis/cytokinesis, muscle contraction, cell adhesion, cell migration and extraversion.

Front 4

Microtubulin is made up of units composed of ⍺β subunits that from dimers. Each monomer weighs 55 kDa each. How long is a dimer?

Back 4

8nm

Front 5

With respect to microtubules; what is the protofilament?

Back 5

A protofilament is a column of alternating ⍺β subunits that run vertically up and down a microtubule.

Front 6

What does it mean for a microtubule to be "Stable"?

Back 6

A microtubule is stable when it is not be depolymerized or polymerized.

Front 7

As a protofilament grows, the GTP bound to which subunit is hydrolyzed?

Back 7

The β subunit's GTP is hydrolyzed to GDP.

Front 8

A singlet tubule is composed of how many protofilaments?

Back 8

13

Front 9

What is the function of 𝛾-Tubulin Ring Complex?

Back 9

It serves as a nucleating site for further polymerization.

Front 10

How many protofilaments are found within a basal body that connects a cilia to the cell?

Back 10

The basal body is composed of 9 triplets. Each triplet contains 13+10+10 protofilaments. The axoneme can also contain a singlet in the centre. So a basal body (like a centriole) contains 9x33= 270 protofilaments or 9*33+13=310 protofilaments depending on whether the singlet exists.

Front 11

Bones (and muscles) are to limbs as ______________ is to cilia and flagella.

Back 11

The axoneme.

Front 12

Structurally, one half of dynein contains two binding domains, and the other half has one binding domain. Which half binds to the microtubules?

Back 12

The half with the two binding domains binds to the microtublues.

Front 13

What proteins would you expect to be involved in intraflagellar transport?

Back 13

The cargo protein (if it is a protein) that needs to get to flagella, dynein for retrograde transport to the cell, and kinesin 2 for anterograde transport to the flagella tip.

Front 14

Many embryonic cells have one single non-motile primary cilium. Which of the following are expected to be a consequence of lacking functional non-motile primary cilium?:

a) Proper cell differentiation

b) Growth

c) Both a) and b)

d) None of the above

Back 14

d) None of the above, consequences of lacking a functional non-motile primary cilium would be improper cell differentiation and lack of growth.

Front 15

You want to image the process of cytokinesis, but not the process of karyokinesis (to the best of your ability). Which of the following proteins should fluorescent probes be made for?:

a) Tubulin

b) Actin

c) Myelin

d) All of the above.

Back 15

b) Actin. The contractile ring that causes cleavage furrow is made up of actin and myosin.

Front 16

Which of the following is the most likely explanation for the decreased half-life of microtubules during mitosis?:

a) The critical concentration of ⍺β-tubulin dimers decreases due to the cytoplasm gaining volume and polymerization is no longer favoured.

b) Kinesin 13 is phosphorylated and becomes inactive.

c) During mitosis the amount of available GTP decreases, which decreases the concentration of GTP bound ⍺β-tubulin dimers and polymerization cannot occur.

d) A microtubule associated protein (MAP) that regularly increases the rate of plus end polymerization is inactivated during mitosis.

Back 16

d) A microtubule associated protein (MAP) that regularly increases the rate of plus end polymerization is is inactivated during mitosis.

(Lecture 2 slide 15)

Front 17

What are the distinctions between astral, polar, and kinetochore tubules?

Back 17

Polar and kinetochore microtubules extend towards the other pole, and are termed kinetochore if they meet and bind a kinetochore, if they do not bind a kinetochore they are termed polar microtubules. Astral microtubules do not extend between poles, rather away from one pole towards the cell membrane.

Front 18

True or False: The plus end of kinetochore microtubules binds directly to the outer kinetochore.

Back 18

False. Plus end must be free to allow for (de)polymerization. Other proteins binds the kinetochore to proteins further down the microtubules.

Front 19

What are the checkpoints in pro metaphase?

Back 19

All chromosomes must be bound by microtubules on both sides and all the chromosomes must be lined up along the equator.

Front 20

True or False. Tension inhibits phosphorylation of Ndc80.

Back 20

True.

Front 21

Which of the following statements are true:

i) During Anaphase A depolymerization occurs at the + and - ends of kinetochore microtubules.

ii) Anaphase B requires motor proteins.

iii) Polymerization of the + end of astral microtubules pulls the poles apart.

iv) Microtubule sliding to push apart poles uses dynein.

Back 21

Only i) and ii). iii) Depolymerization occurs at the + end, iv) kinesin is used.

Front 22

Which of the following proteins can contribute to depolymerization of microtubules?:

a) Stathmin

b) Kinesin 5

c) MAP

d) Both a) and c)

e) All of the above

Back 22

d) Both a) and c). Kinesin 13 depolymerizes, not Kinesin 5.

Front 23

Which of the following molecules can contribute to depolymerization of microtubules?:

a) Taxol

b) Colchicine

c) Both a) and b)

Back 23

b) Colchicine. Taxol stabilizes microtubules.

Front 24

You discover a mutant yeast strain that causes GTP molecules to be permanently bound to both the ⍺ and the β tubulin monomers in the the dimer (doesn't get hydrolyzed). a) How would this mutation affect the critical concentration (Cc)? b) What would be the effect of the microtubules extending into a region where the concentration of dimers is less than the critical concentration? c) What would be the effect of cooling the cells to about 4℃, with respect to the microtubules?

Back 24

a) Unaffected, critical concentration is constant, the only difference is that dimers wouldn't need to be phosphorylated to regenerate ATP.

b) The microtubule would stop growing, but since the β-tubulin ATP cannot be hydrolyzed to ADP the microtubule would not degrade.

c) The protofilaments of the microtubules would break up and the microtubules would degrade.