MCAT Biology : Cell Cycle

Study concepts, example questions & explanations for MCAT Biology

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1

Example Question #1352 : Mcat Biological Sciences

During which of the following portions of the cell cycle is DNA polymerase most active?

Possible Answers:

M

G1

S

G0

Correct answer:

S

Explanation:

By referring to DNA polymerase activity, this question is asking about the portion of the cell cycle that involves DNA replication. S phase is the portion of Interphase during which the cell replicates its DNA.

Example Question #1353 : Mcat Biological Sciences

During which of the following portions of the cell cycle are mRNA and proteins mainly produced?

Possible Answers:

M

G2

G1

S

Correct answer:

G1

Explanation:

By referring to mRNA and proteins, this question is asking about the portion of the cell cycle that involves gene transcription and protein translation. This occurs mostly during growth and organelle replication in the G1 portion of Interphase.

Example Question #1354 : Mcat Biological Sciences

Human chromosomes are divided into two arms, a long q arm and a short p arm.  A karyotype is the organization of a human cell’s total genetic complement.  A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size. 

When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present.  Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome.  Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.

1

A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:

Pic2

Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.

Chromosomes are often made visible using Giemsa staining. This stain shows specific banding patterns for chromosomes, and helps scientists organize them under a microscope. Considering that chromosomes are the standard unit of organization for a cell’s DNA, during which phase of the cell cycle would chromosomes most likely be visible?

Possible Answers:

M phase

Chromosomes are visible during all portions of the cell cycle

S phase

G1 phase

G2 phase

Correct answer:

M phase

Explanation:

Chromosomes are most likely to be visible when a cell is organizing its genetic material, as it would just before it undergoes cytokinesis and becomes two daughter cells. S phase is a tempting answer, as this is when DNA is duplicated, but S phase only encompasses the enzymatic replication of DNA, and not its organization which is characteristic of the much shorter M phase.

Example Question #1 : Cell Cycle

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells. 

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below.  In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

 

Untitled

If the bladder cells are experiencing uncontrolled division in dish 1, they are likely spending abnormally long periods of time in which phase of the cell cycle?

Possible Answers:

G1 phase

G2 phase

M phase

S phase

G0 phase

Correct answer:

M phase

Explanation:

Cell division occurs in M phase. Thus, if the cells are experiencing uncontrolled growth, they are probably remaining in M phase abnormally long.

Example Question #2 : Cell Cycle

There are several methods for analyzing the number of cells undergoing proliferation. Cells or whole organisms can be treated with BrdU, a uracil analog, which is incorporated during DNA synthesis. Cells or tissues can be fixed and BrdU can be detected using BrdU-specific antibodies. Similarly, cells can be fixed without any pretreatment, and proliferation can be detected by antibodies specific for MKI67 or pH3 (phosphorylated histone 3). MKI67 can be detected at all active phases of the cell cycle (not interphase) while pH3 can be detected during mitosis only.

Which detection method should be used to detect the greatest number of healthy cells?

Possible Answers:

MKI67

pH3

BrdU

Each method will detect the same number of proliferating cells

Correct answer:

BrdU

Explanation:

Because cells can be treated with BrdU in advance of analysis, a large window of time can be analyzed. MKI67 and pH3 only measure proliferation at a "snapshot" of time.

BrdU analysis will essentially provide a total number of cells that are capable of proliferating since the initial treatment with BrdU. Any cells that have undergone DNA replication since this addition will be detected, while quiescent or dead cells will not be detected. In contrast, MK167 and pH3 will show only cells that are in the act of proliferation when the sample is taken. Normally replicating cells that are simply in interphase will not be detected, even though they are healthy.

Example Question #1357 : Mcat Biological Sciences

In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:

Untitled

In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.

Which of the following times in the cell cycle is the activity of eIF2 likely to be highest?

Possible Answers:

G1

G0

M

S

G2

Correct answer:

G1

Explanation:

We know that inhibition of eIF2 represses translation. The question asks for the time when eIF2 is most active, thus the time when translation is likely at its highest.

In M phase, the cell is actively dividing. That may make this a tempting answer, but G1 is actually when all of the non-genetic material is doubled. S phase sees the doubling of the genetic complement, and G2 is a major checkpoint stage to ensure everything is ready to go for mitosis.

G1 is the best answer, as this is the period when organelles and cellular proteins are being synthesized.

Example Question #1 : Cell Cycle

During the eukaryotic cell cycle, what is the purpose of the G2/M checkpoint?

Possible Answers:

To ensure that DNA hasn't been damaged during S phase

To ensure that the cell is large enough for cell division

To allow for formation of the spindle fibers

To ensure that the cell is ready to divide

To ensure that all chromosomes are aligned properly for cell division

Correct answer:

To ensure that DNA hasn't been damaged during S phase

Explanation:

The G2 phase occurs after S phase, but before M phase (mitosis). The purpose of the G2/M check point is to ensure there is no DNA damage that occurred during S phase (DNA synthesis). If damage is found, the cell will try to repair and DNA breaks. If the DNA cannot be repaired, the cell will undergo apoptosis. Many cancer suppressor genes, such as p53, are involved in this process of checking the DNA quality.

Example Question #1359 : Mcat Biological Sciences

Which of the following choices will be affected by a cell containing a nonfunctional copy of the protein p53?

I. Apoptotic pathways

II. DNA repair pathways

III. Ability to arrest the cell cycle

Possible Answers:

II only

I, II, and III

I and II

I and III

Correct answer:

I, II, and III

Explanation:

p53 is sometimes referred to as "the guardian of the genome" due to its huge role in suppressing the propagation of cells containing permanent DNA damage. If DNA damage is detected, p53 becomes activated and acts to promote cell cycle arrest. This gives the cell a chance to repair its genome by activating the appropriate DNA repair pathways (for which p53 is also responsible).

p53 also plays a role in promoting apoptosis. If the DNA damage is irreparable, the cell will go through apoptosis to prevent propagation of this damage.

Damage to the p53 gene can lead to unmitigated cell division and tumor formation, marking p53 as a proto-oncogene.

Example Question #1360 : Mcat Biological Sciences

Which of the following factors might cause cell cycle growth arrest?

Possible Answers:

DNA damage

All of these answers

Failure of the chromosomes to line up on the equatorial plate during mitosis

Lack of appropriate growth factors

Correct answer:

All of these answers

Explanation:

All of the choices are potential reasons for cell cycle arrest.

DNA damage activates pathways (commonly through the protein p53) in an attempt to repair the damage or activate apoptotic pathways if the DNA damage cannot be fixed. This causes arrest of the cell cycle at the G2 checkpoint.

Lack of appropriate growth factors will keep the cell from progressing through the cell cycle. Prolonged lack of growth is sometimes referred to as G0 of the cell cycle, and occurs when the cell cannot pass the G1 checkpoint.

Failure to properly align the chromosomes along the equatorial plate during mitosis will prevent the cell from activating pathways to degrade the cohesin that holds the sister chromatids together. This is a method to ensure proper segregation of chromosomes, and is known as the metaphase checkpoint.

Example Question #1332 : Biology

Which process does not occur in the pachytene phase of prophase I?

Possible Answers:

Crossover takes place

None of the other answers

Tetrads move towards the midline

Synapsed chromosomes bunch up and become thick

Synapsis is completed

Correct answer:

Tetrads move towards the midline

Explanation:

During the pachytene stage of prophase I in meiosis, chromosomes have become condensed and form synapses. This is also when crossover, which is important to genetic diversity, takes place.

Tetrads do not move toward the midline until later in the meiotic processes.

← Previous 1
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: