DAT Question of the Day

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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Correct Answer: A. increased production of HCl by parietal cells acts stimulatory on gastrin secretion

Gastrin stimulates parietal cells to release HCl. If A were true, then there would be a positive feedback loop where gastrin is stimulating more HCl production, and HCl is stimulating more gastrin production, causing us to burn a hole through our stomach! Increased production of HCl by parietal cells leads to somatostatin secretion, which inhibits the secretion of gastrin. Lastly, an elevated gastric pH (i.e. low amount of acid) would stimulate the G cells to release more gastrin in an attempt to stimulate the parietal cells to release more HCl to bring the acidity back to normal.

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Correct Answer: C. (1) Sodium (2) Potassium (3) Calcium

Neurons are at rest with a negative membrane potential relative to the outside of the cell. During an action potential, positively charged sodium ions rush into the cell making the membrane potential less negative (depolarization). Soon after, potassium (another positively charged ion) exits the cell and restores polarization. The presynaptic terminal reacts to the action potential by opening calcium channels. This calcium is required for the cellular machinery responsible for neurotransmitter release into the synapse.

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Correct Answer: E. A and C

During the evolution of living systems, there were two ways the velocity of nerve impulse propagation could be increased. The first way was increasing nerve diameter, while the second way was the formation of the myelin sheath. The latter mechanism is less energetically expensive than the former.

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