The small invertebrate krill species Thysanoessa inermis is adapted to cold (4oC) seawater. Over the past ten years, there has been a gradual increase in the water temperature of the krill's habitat. A sustained increase in water temperature may ultimately affect the ability of the krill to survive. One effect of higher temperatures is protein misfolding within cells. Krill have several hsp genes that code for heat-shock proteins (HSPs). These proteins help prevent protein misfolding or help to refold proteins to their normal shapes.
Scientists conducted experiments on T. inermis to detect changes in the expression of hsp genes when the krill were exposed to temperatures above 4oC. An experimental group of krill was maintained in tanks with 4oC seawater and then placed into tanks with 10oC seawater for approximately three hours. The krill were then given a six-hour recovery period in the 4oC seawater tanks. A control group of krill was moved from a tank of 4oC seawater to another tank of 4oC seawater for approximately three hours and then returned to the original tank. The scientists analyzed hsp gene expression by measuring the concentrations of three mRNAs (I, II, Ill) transcribed from certain hsp genes in both the heat-shocked krill (Figure 1) and the control krill. For the control krill, no transcription of the hsp genes was detected throughout the test period (data not shown).
Figure 1. Average concentration of three mRNAs (I, II, Ill) transcribed from hsp genes in krill heat shocked at 10oC. Error bars represent ±.
Identify the hsp mRNA that has the slowest rate of concentration increase in response to heat-shock treatment.
Describe the trend in the average concentration of mRNA I throughout the experiment.
The scientists hypothesized that the heat-shock protein (HSP) translated from mRNA I plays a greater role in refolding proteins than does the HSP translated from mRNA II. Use the data to support the hypothesis.
mRNAs I and II are transcribed from the same gene. Explain how a cell can produce two different mRNAs from the same gene.
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