MCAT Biology : MCAT Biological Sciences
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Example Questions
Example Question #1262 : Biology
Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.
The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.
Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.
A scientist discovers that Neisseria uses flagella to move between host cells. Which of the following is true of the flagella?
They have a 9+2 microtubule ultrastructure
They cannot be an antigen for host immune response
They are more common in eukaryotes than in prokaryotes
They are also used in the female reproductive tract epithelium to move eggs toward the uterus
They are different from cilia in terms of internal structure
They have a 9+2 microtubule ultrastructure
Flagella and cilia share a 9+2 ultrastructure, where there is a ring of 9 doublets of microtubules surrounding a central doublet, and connects via dynein arms.
Example Question #1263 : Biology
Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.
In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.
Phagocytosis of the sort that was involved in endosymbiosis makes use of microtubules to orient the cell appropriately. Which of the following processes also directly uses microtubules?
Translation
Transcription
DNA replication
Mitosis
Golgi modification of proteins
Mitosis
Mitosis makes use of microtubules to organize and move DNA into appropriate daughter cells. These specific structures are known as mitotic spindles.
The other processes are closely linked to protein, enzyme, or ribosome function and do not involve microtubules.
Example Question #1 : Ribosomes And Cytoskeleton
Which of the following is true of microtubules?
Microtubules are involved in phagocytosis
Microtubules are larger than microfilaments
Microtubules are responsible for cytoplasmic streaming
Actin forms a major component of microtubules
Microtubules are larger than microfilaments
Microtubules are a component of the cell cytoskeleton formed by polymers of tubulin protein. They are larger than microfilaments and make up the internal structures of cilia and flagella. Microtubules have a positive and negative end. The negative end of a microtubule attaches to a microtubule-organizing center (MTOC) within the cell, which then allows the microtubule to grow away from the MTOC at its positive end.
Example Question #61 : Cellular Structures And Organelles
Which of the following is not a function of microtubules?
Component of cilia structure
Component of flagella structure
Component of sarcomere scaffold structure
Component of the cytoskeleton
Produce mitotic spindle
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 #71 : Cellular Structures And Organelles
What happens at the minus-end of actin filaments when the concentration of G-actin is above its critical concentration?
Monomers are not lost from it or added on to it.
Monomers bind GTP.
Monomers are lost from it.
Monomers undergo dynamic instability.
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 #71 : Cellular Structures And Organelles
Actin is the major protein that composes which part of the cytoskeleton?
Microfilaments
Microtubules
Cilia
Intermediate filaments
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 #1271 : Biology
Which of the following structures that promote cell motility generates motion by sliding actin microfilaments?
Microvilli
Cilia
All of these answers
Flagella
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 #74 : Cellular Structures And Organelles
Arp2/3 is a protein complex that helps nucleate branch points on __________ chains.
intermediate filament
actin microfilament
glycogen
microtubule
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 #72 : 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
I, II, and III
I and II
III and IV
II, III, and IV
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 #73 : Cellular Structures And Organelles
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.
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