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: D. DNA polymerases require a primer base-paired to the template and with a free 3′-end.

DNA polymerase can add dNTPs (deoxynucleoside triphosphates) only to a pre-existing oligonucleotide chain that is annealed to the template DNA. The enzyme adds dNTPs on a free 3′-OH- group. Primers in replication are RNA based. These primers are then cut out via endonuclease activity and replaced with DNA nucleotides. Finally, DNA ligase fuses the gap between the fragments of DNA.

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Correct Answer: C. prevents glucose from leaking through the plasma membrane.

Glycolysis takes place in the cytosol. It is a characteristic of eukaryotic and prokaryotic cells. The first reaction of glycolysis is irreversible since it requires an energy investment. Glucose-6-phosphate cannot pass back through the plasma membrane.

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Correct Answer: B. Secondary Succession

Succession is the process that ecological areas go through to repopulate a community. Following a forest fire, the environment is beginning from the producers level and must first grow small grasses, then small shrubs, before consumers and higher-level consumers will repopulate the area. In the event of a volcano, this would be an example of primary succession, as there is no soil to sustain plants. Instead, bacteria populate the area, and eventually give rise to soil and plants and animals. Homeostasis refers to the internal regulation of an organism as opposed to the process an external environment goes through. Biological regeneration is a distractor answer choice testing your true knowledge of the topic at hand.

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Correct Answer: C. a homozygous red haired cow

In genetics, a test cross is used to determine the genotype of an organism that expresses the dominant phenotype. The black cow could be BB or Bb for the black hair color. If you were to mate the cow with a homozygous black cow BB, all of the offspring would be black haired and this would not help the farmer determine the genotype of the original black cow. Likewise using a heterozygous black cow (Bb), could result in all black offspring, since there is only a 25% chance of getting a red haired cow if the original cow was heterozygous (Bb). A white cow nor an albino cow are not mentioned in the original question and would not be relevant in determining the genotype of the black cow. A test cross, uses a homozygous recessive individual, since this genotype is easily physically identified. If the 50% of the offspring are black and 50% are red, then the black cow was heterozygous (Bb). If all black offspring result, then the black cow was homozygous dominant (BB).

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Correct Answer: C. a nonsense mutation

A silent mutation often occurs in the wobble site of the codon on the mRNA strand. For most codons, if the third base pair is changed, the correct amino acid can still be made. A missense mutation results in the addition of an incorrect amino acid, but can still lead to a functional protein. Nonsense mutations result in a polypeptide chain that is shorter and is non-functional. For nonsense mutations, an insertion or deletion of a nucleotide base creates a premature stop codon (UGA, UAG, or UAA), terminating translation before the polypeptide can be completed. Transfer mutation is not an accurate term in biology.

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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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