DAT Question of the Day

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: 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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