MCAT Biology : Cellular Structures and Organelles

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1282 : Biology

Which of the following structures is not composed of microtubules?

Possible Answers:

Cilia

Mitotic spindle

Eukaryotic flagella

Prokaryotic flagella

Correct answer:

Prokaryotic flagella

Explanation:

While eukaryotic flagella are composed of microtubules, prokaryotic flagella are composed of a long protein called flagellin. Microtubules are composed of the tubulin protein, and play keys roles in mitosis and cell motility. Cilia and spindle fibers are both composed of microtubules. Prokaryotes do not contain developed microtubules.

Example Question #81 : Cellular Structures And Organelles

Which of the following accurately represents the compositions of eukaryotic cilia and flagella?

Possible Answers:

Nine actin singlets surrounded by two actin doublets

Nine microtubule singlets surrounded by two microtubule doublets

Two microtubule singlets surrounded by nine microtubule doublets

Two actin singlets surrounded by nine actin doublets

Correct answer:

Two microtubule singlets surrounded by nine microtubule doublets

Explanation:

Eukaryotic cilia and flagella are incredibly similar in protein composition. Their primary functions include helping cells move and maintaining fluid flow within the body. They accomplish this by maintaining a structure of 9 microtubule doublets surrounding 2 microtubule singlets (9+2). The motor protein dynein is then responsible for allowing the sliding of filaments that is necessary for movement.

Example Question #11 : Ribosomes And Cytoskeleton

Which of the following choices describes a function of the eukaryotic centriole?

Possible Answers:

Digest foreign pathogens in the cytosol

Catabolize very long chain fatty acids

Produce and organize spindle fibers used during cell division

Condense chromosomes and repackage chromatin

Correct answer:

Produce and organize spindle fibers used during cell division

Explanation:

Centrioles have diverse functions. Particularly, they are important portions of centrosomes and help develop the mitotic spindle that aids in the separation of chromosomes during cell division.

Peroxisomes are responsible for the catabolism of very long chain fatty acids. Lysosomes are responsible for handling pathogens in the cytosol in a process called phagocytosis. The pathogens are then digested by hydrolytic enzymes in the lysosome interior. Chromosome condensation is accomplished by various proteins.

Example Question #1285 : Biology

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.

A scientist is studying microtubules in a series of mitotic cells. He notices that the microtubule structures attach to chromosomes in each mitotic cell by binding to a protein complex at the center of the chromosome. What is the name of this protein complex?

Possible Answers:

Centriole

Centromere

Kinesin

Centrosome

Kinetochore

Correct answer:

Kinetochore

Explanation:

The chromosome is formed by two sister chromatids, connected at a central point to form an "X" structure. This central location is called the centromere.

During prophase, as the chromosomes condense, a protein complex forms at the centromere and becomes bound to microtubule spindle fibers. This protein complex is known as the kinetochore.

Centrioles form the distal attachment points for the microtubules that bind to the kinetochore. During anaphase, the centrioles anchor the spindle fibers at opposite ends of the cell and allow the microtubules to pull the chromatids apart. The centrosome is composed of two centrioles.

Kinesin is a protein capable of traveling along microtubules, helping to assemble and disassemble their structures, as well as shuttling proteins along the length of the tubule.

Example Question #1286 : Biology

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?

Possible Answers:

Telophase

Metaphase

Prophase

Anaphase

Interphase

Correct answer:

Anaphase

Explanation:

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 #1287 : Biology

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?

Possible Answers:

Microtubules have a hollow 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

Actin polymers have a hollow center, are composed of monomers, and are thicker than microtubules

Microtubules have a hollow center, are composed of monomers, and are thicker than actin polymers

Microtubules have a solid center, are composed of dimers, and are thicker than actin polymers

Correct answer:

Microtubules have a hollow center, are composed of dimers, and are thicker than actin polymers

Explanation:

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 #1288 : Biology

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?

Possible Answers:

Kinesin

Lysosome

Golgi body

Basal body

Centrosome

Correct answer:

Centrosome

Explanation:

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?

Possible Answers:

Nucleolus

Mitochondria

Nucleus and mitochondria

Nucleus

Endoplasmic reticulum

Correct answer:

Nucleus and mitochondria

Explanation:

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?

Possible Answers:

Protein synthesis

DNA synthesis

ATP production

Membrane synthesis

rRNA production

Correct answer:

rRNA production

Explanation:

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?

Possible Answers:

Mitochondria

Rough endoplasmic reticulum

Nucleolus

Lysosome

Nucleus

Correct answer:

Nucleolus

Explanation:

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.

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