GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Cytoskeleton Structures

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Help With Cytoskeleton Structures

Which of the following might explain why no known motor proteins have been found to utilize intermediate filaments?

Possible Answers:

Actin and microtubules are non-polar, while intermediate filaments are polar

Microtubules and actin are polarized, while intermediate filaments are not

Intermediate filaments are too small for motor proteins

Intermediate filaments are too large for motor proteins

Correct answer:

Microtubules and actin are polarized, while intermediate filaments are not

Explanation:

One of the most likely explanations for why intermediate filaments have no known motor proteins is because they are nonpolar. What this means is that there are no distinct ends to the filament. Motor proteins have ways of detecting which direction they are moving along actin or microtubules because they have distinct ends (polarization). Size should not affect the ability of a motor protein to function, especially because actin is smaller than intermediate filaments and microtubules are larger (hence the name "intermediate").

Example Question #2 : Help With Cytoskeleton Structures

Which cellular filament is found in the flagella of eukaryotic cells?

Possible Answers:

Collagen

Microfilaments

Intermediate filaments

Microtubules

Correct answer:

Microtubules

Explanation:

Eukaryotic flagella are composed of nine pairs of microtubules. In contrast, prokaryotic flagella are composed of the protein flagellin.

Example Question #3 : Help With Cytoskeleton Structures

Which of the following cytoskeletal components is comprised of G-actin subunits organized in polymers?

Possible Answers:

Microfilaments

Lamin

Microtubules

Intermediate filaments

Septins

Correct answer:

Microfilaments

Explanation:

G-actin subunits that polymerize form microfilaments, also known as actin filaments. The other cytoskeletal components listed are formed from different proteins, but only microfilaments are actin-based structures. 

Example Question #4 : Help With Cytoskeleton Structures

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

Possible Answers:

Axonal transport in neurons

None of these will be affected

Both of these will be affected

Mitosis

Correct answer:

Both 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.

Example Question #5 : Help With Cytoskeleton Structures

A common chemotherapeutic agent, called Vincristine, is used to treat cancers. It acts by inhibiting tubulin. What can you conclude about Vincristine?

I. Vincristine inhibits synthesis of the biggest cytoskeletal element

II. Vincristine can cause neuropathy

III. Vincristine affects muscle contraction by directly altering actin-myosin interactions

Possible Answers:

II and III

I and III

I and II

I, II and III

Correct answer:

I and II

Explanation:

Recall that tubulin is an essential component of microtubules. Administering Vincristine to cancer patients will halt the synthesis of microtubules in cancer cells, thereby inhibiting several essential cellular processes (such as mitosis). This will prevent proliferation of the cancer cells. There are three cytoskeletal elements; microtubules, microfilaments, and intermediate filaments. Of the three, microtubules are the biggest, followed by intermediate filaments. Recall that microtubules are also involved in axonal transport in neurons; therefore, halting microtubule synthesis in neurons could result in nerve problems and neuropathies.

Actin-myosin interactions involved in muscle contraction do not depend on the microtubules; therefore, Vincristine will not affect muscle contraction. Note that actin filaments make up microfilaments; therefore, any damage to actin (and microfilaments) will affect muscle contraction.

Example Question #6 : Help With Cytoskeleton Structures

Which of the following is true regarding microfilaments?

Possible Answers:

They are made up of myosin and actin

More than one of these are true

They are the smallest of the cytoskeletal elements

They always have a 9+2 arrangement

Correct answer:

They are the smallest of the cytoskeletal elements

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.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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