DAT Question of the Day

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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Correct Answer: D. complementary DNA

The genomic library of an organism can be created by using complementary DNA (cDNA). cDNA is synthesized from messenger RNA using reverse transcriptase. Genomic libraries made using cDNA are not complete as the messenger RNA that is transcribed is not an exact complement to the original DNA strand due to the absence of introns.

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Correct Answer: A. moves 3 Na⁺ out and 2 K⁺ in the cell

Maintenance of the cell membrane potential is conducted by keeping a low concentration of Na ions and high concentration of K ions inside the cell. The pump uses ATP energy to expel three Na ions out of the cell. Also, the pump enables entrance of two K ions into cell. However, the resting potential of the membrane IS NOT as a result of pumping out 3 positive ions and only pumping in 2 positive ions. The resting potential is achieved due to the impermeability of the membrane to the ions.

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Correct Answer: C. depolarization of the beta cell membrane leads to an increased level of intracellular Ca2+

To begin, glucose is transported into the beta cell. As a result of glucose metabolism, ATP molecules are generated. An increased level of ATP inhibits the KATP channel, preventing entrance of K⁺ ions into the cell. The consequence of this action is depolarization of the cell membrane and subsequent activation of the VDCC. Ca²⁺ ions enter into the cell stimulating exocytosis of insulin. This is a great example of an application question in the biology section of the DAT.

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Correct Answer: D. The plant went through photosynthesis but at a lower rate than normal.

The plant cell in shade has some access to sunlight, but it is limited since the cell is in the shade. Since methylene blue is in the test tube, the color in the test tube should become darker, more and more blue as the plant produces oxygen and goes through photosynthesis. Plant cell 1 is the control group and as you can see the percent transmittance of light decreases over the 3 days because of the high rate of photosynthesis and production of oxygen. The plant cell in the closet had no access to sunlight and was able to go through some photosynthesis on the first day but virtually none the other 2 days, which is why the percent transmittance remained high, signaling low levels of oxygen produced and low levels of blue pigment present.

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Correct Answer: A. mutation in codon 288

The genetic code is degenerate. It means that a particular amino acid is determined by multiple codons. These codons usually have a different third “letter”. This is known as genetic “wobble”. For example, the amino acid serine is determined by the following codons: TCT, TCC, TCA, TCG. Based on this, a mutation in codon 288 does not change the polypeptide structure because GAA and GAG code for the same amino acid. This mutation will not affect cancer development.

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