Cytoskeleton (Smit)

28 important questions on Cytoskeleton (Smit)

Which of the three filaments that are found in the cytoplasm are the toughest and most durable?

Intermediate filaments

What are the intermediate filaments in the nerve cells called?

Neurofilaments

What are the intermediate filaments in connective tissue, muscle cells, and neuroglial cells called?

Vimentin and vimentin-related
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How is an intermediate filament build up?

First there is a dimer, then a coiled-coil dimer. Following by a staggered tetramer of two coiled-coil dimers. Eight tetramers are twisted into a ropelike filament.

Which intermediate filaments are found in the cytoplasm?

  • Keratin filaments
  • Vimentin and vimentin-related filaments
  • Neurofilaments

What is the function of intermediate filaments in the nucleus?

Intermediate filaments in the cell nucleus strengthen the nuclear membrane.

What protein aids in the bundling of intermediate filaments and links these filaments to other cytoskeletal protein networks?

Plectin

What is the main function of microtubules?

Microtubules have a crucial organizing role in all eukaryotic cells.

What are the structures called where microtubules grow out from?

  • Centrosomes
  • Mitotic spindle
  • Basal body (cilia)

How are microtubules build up?

Tubulin heterodimers (=microtubule subunit) consisting of an α- and a β-tubulin stack together to form the wall of the hollow cylindrical microtubule.

Microtubules are very polar. What makes the plus end and what makes the minus end?

The β-tubulin end is the plus end, the α-tubulin end is the minus end.

What is the function of the γ-tubulin?

γ-tubulin is a ring structure on a centrosome. The microtubules grow out of these rings.

Why do microtubules need nucleating sites such as those provided by the γ-tubulin rings in the centrosome?

It is much harder to start a new microtubule from scratch. In aγ-tubulin ring a tubulin dimer ring is already made.

What is dynamic instability?

Dynamic instability is the phenomenon that microtubules stop to grow and become shorter, following by growth again.

What controls the dynamic instability of microtubules?

GTP hydrolysis

How can microtubules selectively be stabilized?

Using microtubule capping protein.

What are motor proteins?

Motor proteins travel along the microtubule or actin filament, moving cargo from one side to the other.

What are the two types of motor proteins?

  • Kynesins
  • Dyneins

What are the three types of microtubules that are involved in spindle formation?

  • Aster microtubules
  • Kinetochore microtubules
  • Interpolar microtubules

As a cell grows, which microtubule-associated protein pulls the ER membrane outward, stretching it like a net?

Kinesin

As a cell grows, which microtubule-associated protein pulls the Golgi apparatus inward, toward the nucleus?

Dynein

Where are actin filaments located?

(A) Microvilli
(B)  Contractile bundles in the cytoplasm
(C) Fingerlike filopodia protruding from the leading edge of a moving cell
(D) Contractile ring during cell division

How is an actin filament build up?

An actin filament contains of actin monomers that are attached to each other. It contains a minus and a plus end.

What is the growth and shrink process for actin filaments?

Actin monomers in the cytosol carry ATP, which is hydrolyzed to ADP soon after assembly into a growing filament. The ADP molecules remain trapped within the actin filament, unable to exchange with ATP until the actin monomer that carries them dissociates from the filament.
The actin filament loses actin subunits from the minus end, new actin monomers are added at the plus end.

What are examples of proteins involved in the regulation of actin filaments?

  • Bundling protein
  • Severing protein
  • Motor protein
  • Side-binding protein
  • Capping (end-blocking) protein
  • Cross-linking protein

What is the role of actin at the 'leading edge'?

Actin at the 'leading edge' forms lamellipodia and filopodia that are needed to make the cell move.

What is the network called that is actin filament rich and just beneath the cell membrane?

Cell vortex

Do actin filaments grow faster at the plus or minus end?

Actin filaments grow faster at the plus end than they do at the minus end.

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