An experiment of Anfinsen on ribonuclease A (RNase A) showed that proteins can be denatured reversibly by 2-mercaptoethanol and 8 M urea. The protein must therefore renature spontaneously;

a) Remove mercaptoethanol and then removal of the urea

b) Removal of the mercaptoethanol allows the protein to re-form disulfide bonds in the presence of oxygen and then removal of the urea

c) Removal of the denaturant (urea) and reductant (mercaptoethanol) allows the protein to renature and re-form disulfide bonds in the absence of oxygen

d) Adding a small amount of mercaptoethanol to the scrambled protein in the absence of O2 catalyzes its conversion to the active enzyme

Which one of the following steps will leads to regaining of the full activity of ribonuclease A (RNase A)

#Question id: 1803

#Unit 4. Cell Communication and Cell Signaling

What are the main population of human hematopoietic stem cells positive for?

#Question id: 4950

#Unit 3. Fundamental Processes

Temperature-sensitive (ts) mutations, which are one form of conditional lethal mutation, allow cells to grow at one temperature (for example, 30°C) but not at a higher temperature (for example, 42°C). A large number of temperature-sensitive replication mutants have been isolated in E. coli. These mutant bacteria are defective in DNA replication at 42°C but not at 30°C. If the temperature of the medium is raised from 30°C to 42°C, these mutants stop making DNA in one of two characteristic ways. The “quick-stop” mutants halt DNA synthesis immediately, whereas the “slow-stop” mutants stop DNA synthesis only after many minutes. Extracts from quick-stop mutants halt DNA synthesis immediately at 42°C, whereas extracts from slow-stop mutants do not stop DNA synthesis for several minutes after a shift to 42°C. Suppose extracts from a temperature-sensitive DNA helicase mutant and a temperature-sensitive DNA ligase mutant were mixed together at 42°C. Which of the following statements are correct?

A. The mixed extracts should be fully competent for DNA replication at 30°C; that is, the mixture should exhibit a nonmutant phenotype.

B. The defective DNA helicase extract would provide normal DNA ligase, and the defective DNA ligase extract would provide normal DNA helicase.

C. In practice, the behaviors of extracts from slow-stop mutants and from nonmutant cells are easy to distinguish.

D. Because of the extreme complexity of DNA replication and the large number of proteins involved, cell-free extracts are not capable of maintaining DNA replication indefinitely.

#Question id: 24473

#Unit 3. Fundamental Processes

#Question id: 9586

#Unit 6. System Physiology – Plant

The photochemical quantum efficiency (quantum yield) is nearly 100%, the energy conversion efficiency is only 27%, and the overall efficiency of conversion of solar

energy is only a few percent the solar energy storage efficiency is a measure of how much of the energy in the entire solar spectrum is converted to usable form, if it

can be measure in terms of C3 and C4 plant?

#Question id: 2662

#Unit 2. Cellular Organization

In the tryptophan operon, tryptophan serves as ________________.