Cytoskeleton and Cell Motility

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GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Cytoskeleton and Cell Motility

Questions 1 - 10
1

Which of the following is true regarding microfilaments?

They are the smallest of the cytoskeletal elements

They always have a 9+2 arrangement

They are made up of myosin and actin

More than one of these are true

Explanation

Microfilaments are the smallest of the three cytoskeletal elements and are made up of actin filaments (myosin is not found in microfilaments). The 9+2 arrangement is found in microtubules, the biggest cytoskeletal elements. The third cytoskeletal element is called the intermediate filament and is made up of related proteins unique to each intermediate filament.

2

Which of the following is true regarding microfilaments?

They are the smallest of the cytoskeletal elements

They always have a 9+2 arrangement

They are made up of myosin and actin

More than one of these are true

Explanation

Microfilaments are the smallest of the three cytoskeletal elements and are made up of actin filaments (myosin is not found in microfilaments). The 9+2 arrangement is found in microtubules, the biggest cytoskeletal elements. The third cytoskeletal element is called the intermediate filament and is made up of related proteins unique to each intermediate filament.

3

A genetic defect involving the tubulin molecules will affect which of the following processes?

Both of these will be affected

Mitosis

Axonal transport in neurons

None of these will be affected

Explanation

Tubulin is a key protein found in microtubules. Microtubules are large cytoskeletal elements that have several functions inside a cell. One of the biggest use of microtubules arises during mitosis. Recall that chromosomes are pulled apart to opposite ends during the anaphase of mitosis. The rope-like substances that pull these chromosomes to opposite ends of cell are microtubule segments. In addition, microtubules are also involved in axonal transport in neurons. Some nerves (such as sciatic nerve) can have extremely long axons. To maintain the integrity of these distal ends of the axons, nutrients and other important molecules from the cell body of a neuron are carried, along microtubule segments, to axon terminals; therefore, microtubules are also essential for axonal transport.

4

A genetic defect involving the tubulin molecules will affect which of the following processes?

Both of these will be affected

Mitosis

Axonal transport in neurons

None of these will be affected

Explanation

Tubulin is a key protein found in microtubules. Microtubules are large cytoskeletal elements that have several functions inside a cell. One of the biggest use of microtubules arises during mitosis. Recall that chromosomes are pulled apart to opposite ends during the anaphase of mitosis. The rope-like substances that pull these chromosomes to opposite ends of cell are microtubule segments. In addition, microtubules are also involved in axonal transport in neurons. Some nerves (such as sciatic nerve) can have extremely long axons. To maintain the integrity of these distal ends of the axons, nutrients and other important molecules from the cell body of a neuron are carried, along microtubule segments, to axon terminals; therefore, microtubules are also essential for axonal transport.

5

Microtubules are present in which of the following structures?

I. Cilia

II. Flagella

III. Microvilli

I and II

II only

II and III

I, II, and III

Explanation

Cilia, microvilli, and flagella are all protrusions from the cell body. Cilia and flagella have functions in cell motility and contain organized systems of microtubules and motor proteins. Microvilli are often used as mechanosensors and are primarily made of cross-linked actin filaments. Microtubules are, therefore, found primarily in cilia and flagella, but no in microvilli.

6

A mutation in which of the following proteins would affect the functionality of eukaryotic flagella?

I. Dynein

II. Kinesin

III. Myosin

I only

I and II

III only

I, II, and III

Explanation

Eukaryotic flagella are primarily composed of microtubules and the motor protein dynein. Hydrolysis of ATP by dynein produces a sliding movement of the microtubule filaments that produces movement.

Kinesin is a motor protein that associates with microtubules, but it is not present in flagella. Myosin is a motor protein that associates with actin microfilaments.

7

Microtubules are present in which of the following structures?

I. Cilia

II. Flagella

III. Microvilli

I and II

II only

II and III

I, II, and III

Explanation

Cilia, microvilli, and flagella are all protrusions from the cell body. Cilia and flagella have functions in cell motility and contain organized systems of microtubules and motor proteins. Microvilli are often used as mechanosensors and are primarily made of cross-linked actin filaments. Microtubules are, therefore, found primarily in cilia and flagella, but no in microvilli.

8

A mutation in which of the following proteins would affect the functionality of eukaryotic flagella?

I. Dynein

II. Kinesin

III. Myosin

I only

I and II

III only

I, II, and III

Explanation

Eukaryotic flagella are primarily composed of microtubules and the motor protein dynein. Hydrolysis of ATP by dynein produces a sliding movement of the microtubule filaments that produces movement.

Kinesin is a motor protein that associates with microtubules, but it is not present in flagella. Myosin is a motor protein that associates with actin microfilaments.

9

In which of the following processes is the cytoskeleton involved?

I. Contractile ring formed during cytokinesis
II. Anchoring the extracellular matrix
III. Post-translational modification of proteins
IV. Post-transcriptional modification of mRNA

I and II

I, II, and III

I only

II and IV

Explanation

The contractile ring formed during cytokinesis is composed of actin microfilaments (a component of the cytoskeleton) and the motor protein myosin. The extracellular matrix can be anchored to the cell via the actin cytoskeleton or the intermediate filament cytoskeleton, via adherens junctions or desmosomes.

Post-translational modifications of proteins commonly occur in the endoplasmic reticulum or the Golgi apparatus and do not involve the cytoskeleton. The same logic applies for post-transcriptional modifications of mRNA, except these occur in the nucleus.

10

In which of the following processes is the cytoskeleton involved?

I. Contractile ring formed during cytokinesis
II. Anchoring the extracellular matrix
III. Post-translational modification of proteins
IV. Post-transcriptional modification of mRNA

I and II

I, II, and III

I only

II and IV

Explanation

The contractile ring formed during cytokinesis is composed of actin microfilaments (a component of the cytoskeleton) and the motor protein myosin. The extracellular matrix can be anchored to the cell via the actin cytoskeleton or the intermediate filament cytoskeleton, via adherens junctions or desmosomes.

Post-translational modifications of proteins commonly occur in the endoplasmic reticulum or the Golgi apparatus and do not involve the cytoskeleton. The same logic applies for post-transcriptional modifications of mRNA, except these occur in the nucleus.

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