Directions: Read the given passage carefully and answer the questions as follows:
Passage
Symptoms of Parkinson’s Disease, such as tremors, are thought to be caused by low dopamine levels in the brain. Current treatments of Parkinson’s disease are primarily reactionary, aiming to replenish dopamine levels after dopamine-producing neurons in the brain have died. Without a more detailed understanding of the behavior of dopamine-producing neurons, it has been impossible to develop treatments that would prevent the destruction of these neurons in Parkinson’s patients. Recent research provides insight into the inner workings of dopamine-producing neurons, and may lead to a new drug treatment that would proactively protect the neurons from decay. By examining the alpha-synuclein protein in yeast cells, scientists have determined that toxic levels of the protein have a detrimental effect on protein transfer within the cell. More specifically, high levels of alphasynuclein disrupt the flow of proteins from the endoplasmic reticulum, the site of protein production in the cell, to the Golgi apparatus, the component of the cell that modifies and sorts the proteins before sending them to their final destinations within the cell. When the smooth transfer of proteins from the endoplasmic reticulum to the Golgi apparatus is interrupted, the cell dies. With this in mind, researchers conducted a genetic screen in yeast cells in order to identify any gene that works to reverse the toxic levels of alpha-synuclein in the cell.
Researchers discovered that such a gene does in fact exist, and have located the genetic counterpart in mammalian nerve cells, or neurons. This discovery has led to new hopes that drug therapy could potentially activate this gene, thereby suppressing the toxicity of alpha-synuclein in dopamine-producing neurons. While drug therapy to suppress alpha-synuclein has been examined in yeast, fruitflies, roundworms, and cultures of rat neurons, researchers are hesitant to conclude that such therapies will prove successful on human patients.
Alpha-synuclein toxicity seems to be one cause for the death of dopamine-producing neurons in Parkinson’s patients, but other causes may exist. Most scientists involved with Parkinson’s research do agree, however, that such promising early results provide a basis for further testing.
Question for Practice Test: Reading Comprehension - 17
Try yourself:One function of the third paragraph of the passage is to
Explanation
The third paragraph relates the genetic testing in yeast cells to the broader issue of Parkinson’s treatment: “Researchers discovered that such a gene does in fact exist [in yeast cells], and have located the genetic counterpart in mammalian nerve cells, or neurons. This discovery has led to new hopes that drug therapy could potentially activate this gene, thereby suppressing the toxicity of alphasynuclein in dopamine-producing neurons.”
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Question for Practice Test: Reading Comprehension - 17
Try yourself:According to the passage, which of the following represents the chronology of a typical protein life in a healthy yeast cell?
Explanation
The second paragraph states that “high levels of alpha-synuclein disrupt the flow of proteins from the endoplasmic reticulum, the site of protein production in the cell, to the Golgi apparatus, the component of the cell that modifies and sorts the proteins before sending them to their final destinations within the cell.” This implies that proteins in healthy cells are produced in the endoplasmic reticulum, sent to the Golgi apparatus where they are modified, and then shipped to the rest of the cell. This chronology is supported by the information given in the second paragraph.
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Question for Practice Test: Reading Comprehension - 17
Try yourself:It can be inferred from the passage that a yeast cell with toxic levels of alpha-synuclein will die because
Explanation
The second paragraph states that high levels of alpha-synuclein “disrupt the flow of proteins from the endoplasmic reticulum…to the Golgi apparatus.” According to the passage, the Golgi apparatus is responsible for distributing proteins within the cell. It also states that "when the smooth transfer of proteins from the endoplasmic reticulum to the Golgi apparatus is interrupted, the cell dies."
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Question for Practice Test: Reading Comprehension - 17
Try yourself:It can be inferred from the passage that current treatments of Parkinson's Disease
Explanation
The first paragraph states that current treatments “replenish dopamine levels after dopamine-producing neurons in the brain have died.” It goes on to say that “without a more detailed understanding of the behavior of dopamineproducing neurons, it has been impossible to develop treatments that would prevent the destruction of these neurons in Parkinson’s patients.” We can therefore conclude that current treatments are based on an incomplete understanding of the dopamineproducing neuron.
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