DAT Question of the Day

Correct Answer: D. Sarcoplasmic reticulum

Calcium ions are essential for muscle contraction to occur. Without the release of calcium, the myosin head would be unable to bind to the actin at the binding sites. It is the calcium that binds and removes troponin from the myosin binding sites on the actin. This is done when the axon terminal nearest a muscle fiber releases acetylcholine, a neurotransmitter, which then causes the sarcoplasmic reticulum to release calcium into the muscle cell to allow for muscle contraction. The endoplasmic reticulum is responsible for protein modification following translation on a ribosome.

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Correct Answer: D. acrosome

The head of the sperm contains the acrosome, which has specialized enzymes that when released, help the sperm to penetrate and fertilize the egg. A plasmid is a small bacterium that can be used in recombinant DNA formation. The capsid is the protein coat that encapsulates a virus’ genetic material. The flagella are important for motility of the sperm but do not contain any enzymes.

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Correct Answer: C. Estrogen

Follicle stimulating hormone causes the follicle in the ovary to begin to divide to complete meiosis II. The growing follicle that will eventually release the egg during ovulation secretes estrogen. The estrogen then spurs the secretion of luteinizing hormone by the anterior pituitary gland, causing the follicle to rupture and release the egg. It is the estrogen and progesterone that is responsible for readying the endometrium for implantation should fertilization occur.

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Correct Answer: C. Water is reabsorbed into the bloodstream.

The descending loop of Henle is only permeable to water. As the urine moves through the loop of Henle, it will become more concentrated as the water is reabsorbed back into the bloodstream. The ascending loop of Henle is permeable to sodium and during this portion of the loop, the urine will be come more diluted, as sodium ions are reabsorbed into the bloodstream.

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Correct Answer: B. Apoptosis

Apoptosis is programmed cell death or the process by which the cell self-destructs. It can be initiated under number of circumstances, such as when the cell has sustained significant damage to its DNA, and is carried out by a cellular cascade pathway. Apoptosis is beneficial to the organism because it can remove cells before the can become cancerous. Immortalization is a situation in which cells continue to divide past the number of times expected for that cell type. This is a common feature of cancer cells. Cellular senescence is a process of cellular aging in which the cell’s telomeres have shortened (through successive cell divisions) to the point that the cell no longer divides. Necrosis is cell death that is caused by some external insult, usually severe, and is not the result of a controlled, biological phenomenon.

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