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.

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

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?

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.

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?

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?

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:

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?

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

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

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

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

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?

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?