DAT Question of the Day

Correct Answer: C. competitive inhibitor

If the particle can bind to the active site, it is competing for the active site with the substrate. A non-competitive inhibitor would bind to an allosteric site on the enzyme, causing a conformational change to the active site, preventing the substrate from binding. Positive and negative inhibitors are terms that do not exist in biology.

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Correct Answer: C. Complete Dominance

Both of the brothers are phenotypically identical in regards to their hair texture. Genotypically, the two are different, as one is homozygous dominant and the other is heterozygous for hair texture. Despite the genotype differences the brothers are phenotypically similar with their hair texture because the dominant allele is the one being expressed. In both the case of Hh and HH, the presence of the dominant allele results in straight hair. This is due to complete dominance. In incomplete dominance, the heterozygote phenotypically is a hybrid between the two parents (i.e. a red and white flower make a pink flower). Whereas with codominance the heterozygote is phenotypically like both parents, i.e. red and white flower makes white plant with red spots. Law of independent assortment and law of segregation refer to Mendelian genetics, but are not the explanations for the phenotypic similarity between the two genotypes.

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Correct Answer: C. Salt glands secrete the excess salt.

This is a great DAT comprehension question. Let’s run through the answer choices and see what we can eliminate. Choice [A] is wrong because there is no structure in the intestine that can physically eliminate salt. Choice [B] is wrong because most chordates have similar osmolarities. Choice [D] is incorrect because nephrons become longer to resorb MORE ions and water, not less. A classic example are rodents in the desert that have very long loops of Henle to resorb as much water and ions as possible. Lastly, specialized bacteria will still eliminate the salts after they’ve used them, so it does not solve the problem of excessive salt. Choice [C] is correct, sea birds have supraorbital glands, or salt glands, above their eyes, which secrete excess salt from their blood. It functions similar to a kidney, but is much more efficient at excreting salt.

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Correct Answer: B. Transport proteins are often used by many substrates while channel proteins are generally used by ions.

Both of these types of proteins have a large variety in their shapes, sizes, and complexities. Therefore, no generalization can be made about them, and [C], [D], and [E] can be eliminated. Many transport proteins can use passive transport as well via uniport, for example, so [A] can be eliminated too. This leaves [B], where it states that channel proteins are used generally by ions. They aren’t called “ion channels” for nothing!

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Correct Answer: B. A nonsense mutation occurred in the extracted mRNA.

This is a great example of a comprehension DAT biology question. All of the answer choices are plausible, but only one stands out like a sore thumb. A nonsense mutation leads to a premature stop codon in the mRNA, halting translation and the production of the protein, which would lead to a lack of activity. However, this is the least likely situation, as mutations are already very rare. It is much more likely that one of the other scenarios occurred. Leaving the introns (the non-coding regions of the DNA) in the mRNA would destroy the intended enzyme by not allowing it to properly fold, leading to inactivation. Introns are normally removed as mRNA is processed through the nucleus, directly extracting “pre-processed” mRNA would likely leave the introns in place. This is why scientists often use cDNA, or complementary DNA, which is the intended gene sans introns and can be directly translated. Most enzymes also undergo post-translational modifications to become active, such as phosphorylation or get cleaved at a specific environment to control their activity. This is especially useful in the production of pepsin in the stomach; producing an inactive version of pepsin (pepsinogen) allows us to control the activity of the enzyme so it does not end up eating the cell that produced it! Molecular chaperones are often present in cellular translation to help an enzyme fold properly.

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Correct Answer: C. methylation.

The bacterial DNA contains numerous methylated adenines and cytosines. This methylation allows restriction endonucleases to discriminate between the host and viral DNA. Bacterial DNA don’t have nucleosomes and don’t coil.

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Correct Answer: E. Merkel cells.

Merkel cells are oval shaped and usually can be found in clusters under ridged epidermal areas. These are the cells responsible for fine-touch differentiation. Keratinocytes produce keratin and are the cells responsible for creating the skin barrier against infection. Fibroblasts manufacture collagen and are found in the dermal layer since collagen is one of the connective tissues. Melanin, the pigment responsible for skin color, is produced by melanocytes. The function of the Langerhans’ cell is to fight against skin infection by processing microbial antigens.

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Correct Answer: A. NADH and FADH2 are oxidized, hydrogen ions move into the intermembrane space, ATP is generated.

In animal cells the electron transport chain (commonly referred to as the ETC) is instrumental in cellular respiration. During the ETC, the two energy carriers, NADH and FADH2, are oxidized. Their electrons are transferred to the cytochromes embedded in the intermembrane of the mitochondria. As the electrons “jump” along the ETC, hydrogen ions are pumped out of the matrix into the intermembrane space. As a result of the hydrogen ion gradient (an electrochemical gradient), the hydrogen ions move through the ATP synthase out of the intermembrane space back into the matrix, thereby making ATP for the cell. The only answer option that details this process accurately is [A]. Note: NADPH, is an energy carrier in photosynthesis. You can think that the “P” is for plants to help remember, but it is really for phosphorus.

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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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