#Question id: 909
#Unit 1. Molecules and their Interaction Relevant to Biology
Most proteins denature at both high and low pH. At high pH, the ionization of internal tyrosines is thought to be the main destabilizing influence, whereas at low pH, the protonation of buried histidines. A titration curve for the unfolding of the enzyme ribonuclease is shown in Figure. Given the relation between the titration curves for protein unfolding and histidine protonation, which of the following conclusion can be drawn correctly?
A. The sharp transition in graph indicates a highly cooperative process; when the protein starts to unfold, it completes the process rapidly
B. The sharp transition in graph indicates a highly noncooperative process
C. Several buried histidines can ionize when the chain starts to unfold, so that when one goes, they all go together due to cooperative behaviour of protein folding
D. Buried histidine (pK of 4 in this example) becomes accessible to solvent, its pK will shift toward its normal value of 6, significantly steepening its titration curve.
#Question id: 18950
#Unit 13. Methods in Biology
#Question id: 1364
#Unit 4. Cell Communication and Cell Signaling
In mice engineered to overexpress the syndecan-1 gene in the hypothalamic region of the brain and other tissues, normal control of feeding by antisatiety peptides is disrupted, and the animals overeat and become obese. Other studies have shown that syndecan-3 may also be involved in the regulation of feeding behavior. Given the following information, which of these outcomes might you expect in experimentally manipulated mice?
I. Hypothalmic expression of syndecan-3 is increased by fasting.
II. Syndecan-3 knockout mice are resistant to diet-induced obesity.
III. Heparinase can cleave syndecan-3 to release heparin sulfate GAG chains that may suppress the activity of antisatiety peptides and feeding behavior.
Following statements are:
A. Overexpression of heparinase in mice with normal levels of syndecan-3 would result in resistance to diet-induced obesity.
B. In mice with normal levels of syndecan-3, fasting followed by free access to a high-fat diet would lead to resistance to diet-induced obesity.
C. Lack of heparinase in mice with normal levels of syndecan-3 would result in animals that overeat and become obese.
D. Overexpression of heparinase in syndecan-3 knockout mice would reverse the resistance to diet-induced obesity.
Which of the following combination is correct?
#Question id: 1662
#Unit 4. Cell Communication and Cell Signaling
What is the approximate number of D segment genes in the immunoglobulin heavy chain gene locus?
#Question id: 12332
#Unit 10. Ecological Principles