MCAT Biology : Cell Cycle

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #11 : Cellular Processes And Functions

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer. 

Which of the following is/are true regarding the cell cycle?

Possible Answers:

G1 and G2 phase both involve cell growth

G0 phase involves no cell growth

G0 phase and G1 phase both involve increasing the amount of genetic material

More than one of these

Correct answer:

More than one of these

Explanation:

There are four main phases in the cell cycle: G1 phase, S phase, G2 phase, and mitosis (M phase). G1 involves cell growth and preparation for DNA replication, S phase involves replication of the genetic material (DNA), G2 phase involves more cell growth and preparation for mitosis, and mitosis involves the division of the cell into two identical daughter cells. G0 phase is another phase that cells can undergo where they remain quiescent. This phase usually occurs after mitosis, when the cell is preparing to enter the G1 phase. Genetic material is increased in S phase only and cell growth occurs in G1 and G2 phases only, thus two of the answer choices are correct.

Example Question #11 : Cellular Processes And Functions

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer. 

A researcher is analyzing a molecule that stops the progression of the cell cycle. What could be the identity of this molecule?

Possible Answers:

Cyclin-depended kinase

Cyclin-dependent kinase inhibitor

DNA polymerase

p53

Correct answer:

Cyclin-dependent kinase inhibitor

Explanation:

Progression through the cell cycle involves several molecules. There are several checkpoints along the cell cycle to ensure that the cell is ready for the next phase. One of the most important molecules involved in this process are the cyclin-dependent kinases (CDKs). These molecules phosphorylate and activate molecules that are important for the cell cycle. Inhibiting CDKs by an inhibitor will halt the activity of these molecules and, subsequently, the progression of the cell cycle.

DNA polymerase is an enzyme involved in DNA replication. It promotes DNA replication and helps the cell progress through the cell cycle. p53 is a tumor suppressor gene that is important for halting uncontrolled growth of cells. This is one of the most common mutated genes found in tumors. Lack of p53 activity leads to decreased regulation of cell growth. This means that cells can proliferate uncontrollably and can eventually become tumors.

Example Question #11 : Cell Cycle

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer. 

Which of the following phase(s) is/are not preceded by a checkpoint?

Possible Answers:

More than one of these

S phase

G1 phase

G2 phase

Correct answer:

More than one of these

Explanation:

There are three main checkpoints in the cell cycle. The first checkpoint occurs between G1 and S phase. During this checkpoint, the cell checks the stability of DNA molecules and the machinery required for DNA replication. If everything is fine, then the cell progresses into the S phase for DNA replication. The second checkpoint occurs between G2 phase and mitosis. During this checkpoint, the cell checks whether DNA replication occurred properly and whether the cell is ready for cell division. The third and final checkpoint occurs between the metaphase and anaphase of the cell. During this checkpoint, the cell checks whether the spindle apparatus is properly formed for anaphase and subsequent steps in mitosis.

Example Question #291 : Cell Biology, Molecular Biology, And Genetics

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer. 

An organism is found to have a diploid number of 50. How many chromosomes will this organism have at the end of S phase?

Possible Answers:

Correct answer:

Explanation:

DNA replication occurs during the S phase. Upon completion of DNA replication, a cell has a duplicate copy of every chromosome it possesses. Recall that humans have 2 sets of 23 chromosomes (total of 46 chromosomes). For example, there are two different copies of chromosome 1, two different copies of chromosome 2, etc. The two different copies of chromosomes are termed homologous chromosomes. Upon completion of DNA replication, each of these 46 chromosomes will have an identical duplicate copy, called the sister chromatid. The sister chromatid is attached to the original chromosome at the centromere. This entire entity, however, is still considered a single chromosome; therefore, upon completion of S phase humans will have 46 chromosomes.

The organism in the question has 50 chromosomes to begin S phase (2n = 50); therefore, it will have 50 chromosomes at the end of S phase.

Example Question #11 : Cell Cycle

The central nervous system consists of the brain and the spinal cord. In general, tracts allow for the brain to communicate up and down with the spinal cord. The commissures allow for the two hemispheres of the brain to communicate with each other. One of the most important commissures is the corpus callosum. The association fibers allow for the anterior regions of the brain to communicate with the posterior regions. One of the evolved routes from the spinal cord to the brain is via the dorsal column pathway. This route allows for fine touch, vibration, proprioception and 2 points discrimination. This pathway is much faster than the pain route. From the lower limbs, the signal ascends to the brain via a region called the gracile fasciculus. From the upper limbs, the signal ascends via the cuneate fasciculus region in the spinal cord.

One of the difficulties in treating spinal injuries is the inability to promote neural cells to regenerate. During which stage of the cell cycle are neural cells arrested in? 

Possible Answers:

Correct answer:

Explanation:

Neural Cells are arrested in the  phase to prevent growth. This arresting phase prevents abnormal growth and cancer cells development.  and  involve cell growth and duplication of organelles.  phase is the time in which DNA is duplicated, and  phase stands for mitosis, or meiosis, in which the nucleus divides.

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