All MCAT Biology Resources
Example Questions
Example Question #1 : Ribosomes And Cytoskeleton
Which of the following is not a function of microtubules?
Component of cilia structure
Produce mitotic spindle
Component of the cytoskeleton
Component of flagella structure
Component of sarcomere scaffold structure
Component of sarcomere scaffold structure
Microtubules are made of the tubulin protein and play integral roles in cell structure. They are prominent in the cytoskeleton and form the fundamental structures for cilia and flagella. The mitotic spindles are also comprised of microtubules, and are used to draw apart the sister chromatids of each chromosome during cell division.
Microtubules do not play a significant role in the structure or function of sarcomeres. Actin and myosin compose the main functional basis of the sarcomere, while titin and the Z disc proteins provide the sarcomere structure.
Example Question #1 : Ribosomes And Cytoskeleton
What happens at the minus-end of actin filaments when the concentration of G-actin is above its critical concentration?
Monomers bind GTP.
Monomers undergo dynamic instability.
Monomers are lost from it.
Monomers are not lost from it or added on to it.
Monomers add on to it.
Monomers add on to it.
Monomers are lost when concentration of G-actin is below its critical concentration. Monomers are gained when concentration of G-actin is above its critical concentration. If it is in between the critical concentrations, the actin filaments will undergo treadmilling, which is the addition of monomers on the (+) end and loss of monomers on the (–) end.
Example Question #2 : Ribosomes And Cytoskeleton
Actin is the major protein that composes which part of the cytoskeleton?
Intermediate filaments
Cilia
Microfilaments
Microtubules
Microfilaments
The cytoskeleton is important for cell support and movement. It is composed of microfilaments made of actin, microtubules made of tubulin, intermediate filaments that bear tension, and cilia/flagella which are made of microtubules (tubulin).
Example Question #6 : Ribosomes And Cytoskeleton
Which of the following structures that promote cell motility generates motion by sliding actin microfilaments?
Flagella
All of these answers
Cilia
Microvilli
Microvilli
The only choice that consists of actin microfilaments is microvilli. These motile structures are composed of cross-linked actin microfilaments. Cilia and flagella are composed of a "9+2" organization of microtubule doublets and singlets (nine doublets surrounding two singlets).
Example Question #1 : Ribosomes And Cytoskeleton
Arp2/3 is a protein complex that helps nucleate branch points on __________ chains.
glycogen
intermediate filament
microtubule
actin microfilament
actin microfilament
Arp2/3 is a large protein complex that is specifically responsible for aiding in the organization of the actin microfilament cytoskeleton. In particular, it helps nucleate branch points from already formed actin microfilaments. Arp2/3 is not involved in the branching of microtubules, intermediate filaments, or glycogen.
Example Question #71 : Cellular Structures And Organelles
In which of the following structures do actin microfilaments play a crucial role?
I. Contractile ring formed during cytokinesis
II. Sarcomeres
III. Adherens junctions
IV. Eukaryotic flagella
I, II, III, and IV
III and IV
II, III, and IV
I and II
I, II, and III
I, II, and III
Eukaryotic flagella are primarily made up of microtubule doublets and singlets organized in a "9+2" manner (two singlets surrounded by nine doublets). Actin microfilaments are not present in flagella.
The contractile ring formed during cytokinesis consists of actin and myosin, and helps separate the two daughter cells to conclude mitosis. Sarcomeres consist of actin and myosin overlaps that are crucial to muscle contraction. Adherens junctions are specialized cell junctions that use the actin cytoskeleton to anchor adjacent cells.
Example Question #1271 : Biology
Desmosomes are specialized cell junctions that anchor cells to one another by connecting the __________ of the cytoskeleton to transmembrane proteins known as __________.
microtubules . . . integrins
intermediate filaments . . . cadherins
actin . . . integrins
actin . . . cadherins
intermediate filaments . . . cadherins
Desmosomes are specialized cell junctions that are important in anchoring certain cell types to one another. Intermediate filaments are used to stabilize these connections by interacting with cadherins. Cadherins are transmembrane proteins that interact with cadherins of adjacent cells on the exoplasmic face of the plasma membrane. Adherens junctions have similar function,s but make use of actin and integrins/cadherins.
Example Question #12 : Ribosomes And Cytoskeleton
Which of the following statements is true about intermediate filaments?
I. Intermediate filaments display treadmilling
II. Intermediate filaments maintain a tightly regulated gradient of ADP/ATP bound monomers
III. Intermediate filaments play a crucial role in the function of desmosomes
IV. Intermediate filaments are a major component of the mitotic spindle
I and II
III only
I, II, III, and IV
I, II, and III
III only
Intermediate filaments are a component of the cytoskeleton that do not display treadmilling. Both actin microfilaments and microtubules undergo treadmilling, during which the structure is built on one end and deconstructed at the other. The result is an apparently "moving" structure with a forward and reverse end. Intermediate filaments are nor polarized and have no distinct ends, making them incapable of this action.
Actin microfilaments and microtubules also maintain gradients of ADP/ATP or GDP/GTP bound monomers respectively, used to indicate their polarity, while intermediate filaments do not. The mitotic spindle is made of microtubules.
Desmosomes, however, are specialized cell junctions that use the intermediate filament cytoskeleton to anchor adjacent cells. Membrane proteins called cadherins bind to the filaments on the intracellular surface of the membrane and bind to the extracellular regions of membrane proteins on the adjacent cell. The result is two intermediate filaments, linked by the bound proteins, to form a junction.
Example Question #1272 : Biology
Primary ciliary dyskinesia (PCD) is a rare genetic lung disorder, also known as immotile cilia syndrome, and is associated with Kartegener's Syndrome. For people with PCD, the tiny hair-like structures (cilia) in the respiratory tract become non-motile.
What is the most likely clinical manifestation of this disease?
Mucus accumulates in the lungs
Lung cells can no longer divide
The lungs lose their ability to expand
Lung tissue becomes more elastic
Oxygen becomes trapped in the lungs
Mucus accumulates in the lungs
Mucus begins to accumulate in the lungs because the cilia no longer move. Cilia function in pushing mucus up the respiratory tract so that it doesn't build up in the lungs. When they become non-motile, they lose this capability.
Example Question #1273 : Biology
The cytoskeleton acts as a scaffold for the cell and maintains cellular integrity. Which of the following is a component of the cytoskeleton?
Flagella
Cilia
Spindle complexes
Actin filaments
Myosin filaments
Actin filaments
The cytoskeleton is comprised of actin filaments, intermediate filaments, and microtubules.
Spindle complexes are found within cells undergoing mitosis; they are made of microtubules, but are not a fundamental part of the cytoskeleton. Cilia and flagella are also largely composed of microtubules; however, these structures are also not fundamental components of the cytoskeleton. Myosin filaments work in coordination with actin filaments during muscle contraction, but are not involved in the cytoskeleton.
Certified Tutor
All MCAT Biology Resources
![Learning Tools by Varsity Tutors](https://vt-vtwa-app-assets.varsitytutors.com/assets/problems/og_image_practice_problems-9cd7cd1b01009043c4576617bc620d0d5f9d58294f59b6d6556fd8365f7440cf.jpg)