DAT Question of the Day

Correct Answer: A. Prophase I

The process described is crossing over. Crossing over occurs during the first stage of meiosis called prophase I. In this stage the homologous chromosomes begin to come together and they form tetrads. The homologous chromosomes are able to “cross over” sections of the chromosome between the homologous pair. The point at which the new chromosomal pieces attach is referred to as the chiasmata.

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Correct Answer: B. Golgi apparatus.

The Golgi apparatus is an organelle which somewhat resembles a stack of pita bread or pancakes. Its purpose is to modify proteins that are manufactured by the endoplasmic reticulum. Within the Golgi are resident enzymes, which catalyze the cargo proteins. The modification processes are glycosylation – the adding or removing of sugars from the protein, sulfation – addition of sulfate groups and phosphorylation – adding phosphate groups.

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Correct Answer: B. perforin

Cytotoxic T-cells are able to rid the body of infections that have spread to cells. To do this, cytotoxic T-cells release perforin, which disintegrates the cell membrane, causing the infected cell to lyse and then be engulfed by macrophages. Antibodies are released from B-cells that then aggregate to an antigen, tagging it to be eaten by macrophages. Actin and tubulin are proteins present in the cytoskeleton and histamine is a chemical released during an allergic reaction or to initiate an inflammatory response.

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Correct Answer: C. pH levels

The brain triggers the diaphragm to contract and lower to spur inhalation when the pH levels begin to drop. In the presence of high amounts of CO2, the blood’s pH begins to become acidic, which is detected by chemoreceptors. This will initiate inhalation, where CO2 will be expelled and oxygen will be absorbed into the capillaries in the alveoli, thereby restoring blood’s neutral pH.

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Correct Answer: B. mycorrhizae

The mycorrhizae inhabit the roots of vascular plants and help to increase the surface area of the roots leading to higher rates of nutrient and water absorption. Rhizomes are underground stems that can sprout to produce new shoots and roots for the plant. Likewise, the apical meristem is the portion on the stem that enables upward growth of the stem. The vascular cambium produces secondary xylem and phloem that help sustain the plant as it grows laterally each year. In addition, the cork cambium forms the “woody” part of the plant helping to provide the plant with structure and support as it grows laterally.

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Correct Answer: B. recombinant DNA

The phenotype of the offspring is a mixture of the two parents’ phenotype. This would be due to recombinant DNA, specifically crossing over that likely occurred during meiosis I (prophase I). Restriction enzymes cut the DNA at specific sequences and would not be the direct cause of the change in phenotype observed. Genetic drift describes the change in allele frequency over time not in one generation. Genetic mutations can lead to different features in an offspring than what was present in the parents, however the offspring resemble the parents, with one phenotypic characteristic from each parent expressed.

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Correct Answer: C. Lambdaphage viral vector.

The lambdaphage viral vector can be used injecting a specific sequence of DNA into a target cell, but not for encouraging the cell to uptake plasmid DNA. Bacteria can utilize a pillus for conjugation, in order to exchange genetic material through plasmids. Electroporation involves using a small charge to cause the cell membrane to become more porous and uptake a plasmid. Heat shock involves heating up the target cells to ~42ºC after keeping them on ice in the presence of CaCl2 – the cell membranes will become more porous and uptake the plasmid as with electroporation.

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Correct Answer: C. CUG ACG UUA

The tRNA has the anticodon to the codon on the mRNA. To solve this problem, you must first transcribe the mRNA from the given DNA strand, which would result in: GAC UGC AAU. Note: For the mRNA, A (Adenine) pairs with U (Uracil) not T (Thymine). Next, you have to find the complementary bases to the mRNA to determine the anticodon. So, the anticodon would be: CUG ACG UUA.

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Correct Answer: C. animal pole

The animal pole does not have yolk and can divide through mitosis at a quicker rate than the vegetal pole (the region with the yolk). The placenta is not known as having high rates of mitosis and is best known as the structure for which the embryo can release waste, perform gas exchange and nutrient absorption.

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Correct Answer: A. Testes

This is a great example of a conceptual question on the DAT. There are many pieces of information here, but if we take it one step at a time, it really isn’t that bad.

First, we have to explain why Cell Type 2 has such a low intracellular concentration compared to the other Cell Types. Recall that steroid hormones are lipid-soluble, which means they freely diffuse through the cell membrane.

In contrast, peptide hormones are stored in granules and are only released when stimulated. So from this information, we can deduce that Cell Type 2 must be synthesizing a steroid hormone, and the other Cell Types must be a variant of a peptide hormone.

As Cell Type 2 was synthesizing its steroid hormone, it was just freely diffusing out, and not building up in concentration inside the cell, so when the researcher measured the intracellular concentration, she barely found any steroid hormone at all. In contrast, Cell Type’s 1, 3, 4, and 5 were synthesizing peptide hormones and building up their concentrations because they store peptide hormones in granules.

Lastly, the question asks where Cell Type 2 possibly came from. Cell Type 2 would need to be harvested from a part of the body that produces steroids, of which there are three main centers, and those are:

1. Adrenal cortex, which produces mineralocorticoids and glucocorticoids like aldosterone and cortisol. It also is a secondary site for androgen synthesis.

2. Testes, which mainly secrete testosterone in relation to hormone synthesis.

3. Ovaries, which mainly secrete estrogen and progesterone in relation to hormone synthesis.

Note: The placenta also produces steroid hormones during pregnancy.

Thus, the correct answer to this question is [A], the testes, as it is the only organ listed that synthesizes steroid hormones.
All of the other answer choices describe organs that do not produce steroid hormones, and are therefore incorrect.

B. Adrenal medulla – Composed mainly of chromaffin cells, which synthesize catecholamines (epinephrine, norepinephrine, and dopamine) from tyrosine.

C. Anterior pituitary – Produces FSH, LH, ACTH, TSH, Prolactin and GH. (Remember the acronym FLAT PiG).

D. Pineal gland – The pineal gland is responsible for synthesizing melatonin.

E. Pancreas – Synthesizes several important peptide hormones, including insulin, glucagon, and somatostatin.

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