DAT Question of the Day

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: D. Obligate Anaerobes

The term obligate means that this is a required condition that has to be met to ensure the viability of the organism. An obligate aerobe has to have oxygen present to be able to survive, like humans. Likewise, an organism that cannot live in the presence of oxygen would be an obligate anaerobe. Facultative anaerobes can survive in the presence of oxygen, but prefer aerobic environments. Permissive anaerobe is a term that does not exist in biology. Aerotolerant organisms do not require oxygen, but they are not poisoned by it either.

1. Obligate aerobes need oxygen to survive because they rely on aerobic respiration.
2. Obligate anaerobes cannot survive with oxygen.
3. Facultative anaerobes grow with or without oxygen, but prefer oxygen environments because they can generate more ATP through aerobic respiration.
4. Microaerophiles need oxygen to survive, but they are poisoned by high concentrations of oxygen.
5. Aerotolerant organisms do not require oxygen, but they are not poisoned by it either.
Source from Wikipedia

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Correct Answer: D. Stimulate sodium reabsorption by the kidneys.

When the adrenal cortex secretes glucocorticoids, many actions are initiated. Cortisol, for example, is released during times of stress. Gluconeogenesis (the process of creating glucose from non-carbohydrates) and lipolysis (the breakdown of fats) are both activated to generate more energy for the both during times of stress. Immunologic response, inflammatory response, glucose uptake by muscle and fat tissues, and protein construction are all restricted as these are energetically expensive and the body needs to place its energy reserves into other areas. Sodium reabsorption by the kidneys is regulated by secretion of mineralocorticoids of the adrenal cortex, such as aldosterone.

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