DAT Question of the Day

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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Correct Answer: C. archaebacteria

The bacteria were found in a hot spring where most bacteria would not be able to grow. Also, the cell wall of the bacteria is composed of a polysaccharide. Eubacteria would not be present in harsh conditions and would also have a cell wall composed of peptidoglycan. Archaebacteria are able to withstand harsh conditions and generally have cell walls made of polysaccharides or lipid based substances. Deuterostome and protostomes are biology terms but refer to the differentiation of the first opening in the blastopore for animals, not bacteria. Eukaryotes do not as a general group all have cell walls and most cannot live in harsh environments.

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Correct Answer: D. plasmodesmata

Tight junctions create a tight seal between adjacent cells, whereas desmosomes serve to adhere cells together anchoring them to one another. Gap junctions allow for adhesion and transport of cytoplasmic materials between neighboring animal cells. The question refers to plant cells and this specialized cellular junction is referred to as the plasmodesmata.

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Correct Answer: B. chromatin

In interphase the DNA is scattered throughout the nucleus. It is during prophase of mitosis and meiosis that the DNA becomes tightly packed, wrapping around histones and forming the tightly coiled chromosomes. A nucleosome is a unit of DNA wrapped around a histone. It is these nucleosomes that wrap around each other to make the super coiled DNA structure. Sister chromatids are formed when the chromosome condenses in prophase.

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Correct Answer: A. Golgi Body

The golgi body assists in the processing of proteins by modifying and sorting the protein. In addition, the golgi body is responsible for tagging and dispersing proteins that are destined to leave the cell. These proteins are packaged in transport vesicles that are then taken to the cell membrane, where the vesicle fuses with the membrane and ejects the protein outside of the cell. The ribosome and rough endoplasmic reticulum both help with protein synthesis but are not responsible for vesicle production. The mitochondria is the site of ATP production during cellular respiration and does not directly form vesicles. The smooth endoplasmic reticulum is essential in lipid production and detoxifying the cell.

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Correct Answer: D. Pineal gland

Melatonin is a naturally produced hormone that helps to regulate the sleep-wake cycle. This hormone is produced by the pineal gland, a small cone-shaped gland located in the central region of the brain.

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Correct Answer: D. the concentration of sodium ions in the extracellular space is greater than the concentration of potassium ions inside the axon.

In a resting neuron, there is more potassium ions inside of the axon than outside in the extracellular space. Likewise there is more sodium in the extracellular space than inside of the axon. The difference in the concentrations of the ions results in a resting potential inside of the axon of -70mV (in humans). When the action potential occurs, sodium/potassium channels open, allowing the free movement of sodium ions into the axon and potassium ions out of the axon. This causes the axon to depolarize and become positive. After the action potential, the resting potential is restored using the sodium/potassium pumps.

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