All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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?
Microtubules and actin are polarized, while intermediate filaments are not
Intermediate filaments are too small for motor proteins
Actin and microtubules are non-polar, while intermediate filaments are polar
Intermediate filaments are too large for motor proteins
Microtubules and actin are polarized, while intermediate filaments are not
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 #1 : Help With Cytoskeleton Structures
Which cellular filament is found in the flagella of eukaryotic cells?
Microtubules
Microfilaments
Collagen
Intermediate filaments
Microtubules
Eukaryotic flagella are composed of nine pairs of microtubules. In contrast, prokaryotic flagella are composed of the protein flagellin.
Example Question #2 : Cytoskeleton And Cell Motility
Which of the following cytoskeletal components is comprised of G-actin subunits organized in polymers?
Lamin
Septins
Microtubules
Intermediate filaments
Microfilaments
Microfilaments
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?
Axonal transport in neurons
Mitosis
Both of these will be affected
None of these will be affected
Both of these will be affected
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
II and III
I and III
I, II and III
I and II
I and II
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 #1 : Cytoskeleton And Cell Motility
Which of the following is true regarding microfilaments?
More than one of these are true
They are the smallest of the cytoskeletal elements
They always have a 9+2 arrangement
They are made up of myosin and actin
They are the smallest of the cytoskeletal elements
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.
Example Question #1 : Cytoskeleton And Cell Motility
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 only
II and IV
I, II, and III
I and II
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.
Example Question #51 : Cellular Structures And Functions
A mutation in which of the following proteins would affect the functionality of eukaryotic flagella?
I. Dynein
II. Kinesin
III. Myosin
I, II, and III
I only
III only
I and II
I only
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.
Example Question #4 : Cytoskeleton And Cell Motility
Microtubules are present in which of the following structures?
I. Cilia
II. Flagella
III. Microvilli
I, II, and III
I and II
II and III
II only
I and II
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.
Example Question #1 : Cytoskeleton And Cell Motility
Which cell organelle can be described as a big tail projecting from the cell like a motor?
Centriole
Cytoskeleton
Flagellum
Mitochondrion
Pilus
Flagellum
Flagella are long, hair-like extensions of the plasma membrane. The movement of flagella propel some cells through fluid.
Mitochondria are the site of the reactions of aerobic metabolism and ATP synthesis. Centrioles consist of microtubules at the base of cilia and flagella, and are involved in spindle cell formation during cell division. The cytoskeleton is a network of protein fibers in the cytoplasm that give shape to a cell and is typically involved in cell movement. A pilus is a hair-like projection located on the surface of certain bacteria and is typically used to attach a bacterium to another cell.
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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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