MCAT Biology : Cell Biology, Molecular Biology, and Genetics
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Example Questions
Example Question #82 : Cellular Structures And Organelles
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Microtubules involved in the vesicular transport model are similar to microtubules that are involved during mitosis. Which of the following phases of mitosis is likely to involve chromosomes moving the greatest distance along microtubules?
Telophase
Anaphase
Interphase
Prophase
Metaphase
Anaphase
Microtubules form the basis of the spindle fiber structures responsible for separating sister chromatids during mitosis. These fibers attach to chromosomes at the centromere by binding to the kinetochore during metaphase. During anaphase, the microtubules retract, pulling apart the sister chromatids and sequestering them in opposite ends of the cell. As a result, anaphase is likely to be the phase during which movement along microtubules is greatest.
Example Question #83 : Cellular Structures And Organelles
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
Which statement is true of microtubules and actin?
Actin polymers have a hollow center, are composed of monomers, and are thicker than microtubules
Microtubules have a solid center, are composed of dimers, and are thicker than actin polymers
Actin polymers have a hollow center, are composed of dimers, and are thicker than microtubules
Microtubules have a hollow center, are composed of dimers, and are thicker than actin polymers
Microtubules have a hollow center, are composed of monomers, and are thicker than actin polymers
Microtubules have a hollow center, are composed of dimers, and are thicker than actin polymers
Microtubules are composed of the protein tubulin, a GTP-binding protein, which forms a ring around a hollow center. This is in contrast to actin, a protein that forms microfilaments, which are thinner than a tubulin-based microtubule.
Example Question #84 : Cellular Structures And Organelles
There are two models for the operation of the Golgi apparatus in eukaryotic cells. As it is difficult to visualize the operation of cells at the molecular level in real time, scientists typically rely on static electron micrographs to see the morphology of organelles. As a result, the dynamic operation of these organelles can sometimes be unclear.
Cisternal Maturation Hypothesis
In the cisternal maturation hypothesis, the cisternae of the Golgi apparatus evolve. Proteins leave the endoplasmic reticulum, and enter the cis-Golgi. The cisterna of the cis-Golgi then matures, with its enzymatic contents and internal environment changing as it becomes the medial-Golgi, and, eventually, the trans-Golgi.
In this model, the proteins never physically leave their membrane-bound cisternae during their transit across the Golgi. Instead, the entire unit of contents remains within the evolving cisternae.
Vesicular Transport Hypothesis
In contrast to the cisternal maturation hypothesis, the vesicular transport hypothesis posits that the cis-, medial-, and trans-Golgi cisternae are more static structures. Instead of evolving around their contents, the contents are physically shuttled via vesicular intermediates from each cisterna to the next.
In the case of vesicular transport, vesicles are shuttled along microtubules. Motor proteins facilitate this movement, with unique proteins being used for each direction of movement along a microtubule.
In addition to their role in vesicular transport, microtubules are central to the proper functioning of many additional cell functions. One such function is the transport of neurotransmitters to the synapse from the soma of the neuron. What structure in the neuron likely organizes the microtubules, and prevents premature depolymerization?
Kinesin
Golgi body
Lysosome
Centrosome
Basal body
Centrosome
The centrosome, with its constituent centrioles, constitutes the microtubule-organizing center of the cell. The main purpose of this center is to anchor the microtubules at one end, and prevent this end from depolymerizing. The centrosome serves to provide direction for microtubules and is a control center for many intracellular movement and shuttling processes. For a vesicle of neurotransmitter to move across the soma, down the axon, and to the synapse, the centrosome must coordinate the assembly of the microtubule structure that carries the vesicle.
Example Question #1 : Nucleus And Nucleolus
Which organelles contain genetic material?
Nucleus
Nucleus and mitochondria
Endoplasmic reticulum
Mitochondria
Nucleolus
Nucleus and mitochondria
The nucleus contains the genetic code of each individual, and the mitochondria is a semiautonomous organelle that contains mitochondrial DNA (passed through the maternal line). mDNA codes specifically for the proteins involved in the electron transport chain, allowing for their implantation in the inner mitochondrial membrane without having to be synthesized elsewhere in the cell.
Example Question #2 : Nucleus And Nucleolus
What is the direct role of the nucleolus in the cell?
DNA synthesis
Protein synthesis
ATP production
Membrane synthesis
rRNA production
rRNA production
The nucleolus, which is located in the nucleus, is directly involved in the production of rRNA. The rRNA composes the ribosome structure, and is directly involved in synthesis of protein.
Example Question #3 : Nucleus And Nucleolus
Where is ribosomal RNA synthesized in eukaryotic cells?
Lysosome
Nucleolus
Rough endoplasmic reticulum
Mitochondria
Nucleus
Nucleolus
The nucleolus is a structure within the nucleus, and is the site of rRNA synthesis. The individual subunits of the ribosome assemble in the nucleus, are exported through the nuclear pores, and are finally brought together into function units in the cytosol.
The nucleus contains DNA, the lysosome has enzymes that break down molecules, and the mitochondria are the site of ATP production. The rough endoplasmic reticulum has a surface that is studded with ribosomes, and works in coordination with these ribosomes to modify proteins after synthesis.
Example Question #241 : Cell Biology, Molecular Biology, And Genetics
The __________ is a structure where ribosomes are formed and the site where __________ is transcribed.
nuclear pore . . . mRNA
nucleolus . . . miRNA
nucleolus . . . rRNA
nuclear pore . . . tRNA
nucleolus . . . rRNA
The nucleolus is a special structure within the nucleus that is responsible for the transcription of rRNA genes and the formation of ribosomal subunits. Transcription of mRNA, tRNA, and miRNA occurs in other regions of the nucleus. Nuclear pores are highly regulated structures that allow for import and export of materials in the nucleus.
Example Question #242 : Cell Biology, Molecular Biology, And Genetics
The construction of ribosomal subunits is accomplished by which cellular structure?
Golgi apparatus
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Nucleolus
Nucleolus
The nucleolus is located inside of the eukaryotic nucleus. It is responsible for the creation of the ribosomal subunits, as well as the rRNA that will be incorporated into the ribosomes. Ribosomal subunits are synthesized in the nucleolus and exported to the cytoplasm, where they can be assembled into functional translation complexes.
The rough endoplasmic reticulum contains ribosomes embedded in its membrane and is responsible for synthesizing certain proteins. The smooth endoplasmic reticulum is responsible for metabolizing toxins and synthesizing lipids. The Golgi apparatus plays a key role in protein sorting, packaging, and transport within vesicles.
Example Question #243 : Cell Biology, Molecular Biology, And Genetics
Which of the following choices can be passed through a nuclear pore complex?
I. pre-mRNA
II. Ribosomal subunits
III. Transcription factors
IV. Mitochondria
I, III, and IV
I, II, III, and IV
I, II, and III
I and III
I, II, and III
The only option that cannot pass the nuclear envelope from the nucleus is mitochondria. Mitochondria range from 0.5-1.0 micrometers, while nuclear pore complexes are about 120 nanometers in diameter. That being said, mitochondria are too large to fit through a nuclear pore complex.
Ribosomes, pre-mRNA, and proteins (such as transcription factors) are all perfectly capable of moving through the nuclear pore complexes, given the appropriate environment.
Example Question #244 : Cell Biology, Molecular Biology, And Genetics
Which of the following is not true of eukaryotic nuclei?
The nucleus is surrounded by two membranes
Assembly of ribosomal subunits occurs in the nucleus
Nuclei are typically supported by a network of intermediate filaments
Chromosomes are randomly distributed around the nucleus
Chromosomes are randomly distributed around the nucleus
Ribosomal subunits are synthesized in the nucleolus, which is located inside the nucleus. The nucleus is surrounded by two membranes, known as the nuclear envelope, studded with large nuclear pore complexes. Import and export of substances through the pore complexes is highly regulated. Nuclei are supported by what is known as a nuclear lamina. This nuclear lamina is composed of intermediate filaments that provide support and structure for the nucleus.
It has recently been shown that chromosomes are not randomly distributed through the nucleus. Chromosomes occupy specific regions of the nucleus, which are currently referred to as "nuclear territories".
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