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: 392

#Unit 1. Molecules and their Interaction Relevant to Biology

When an ionic compound such as sodium chloride (NaCl) is placed in water, the component atoms of the NaCl crystal dissociate into individual sodium ions (Na+) and chloride ions (Cl-). In contrast, the atoms of covalently bonded molecules (e.g., glucose, sucrose, glycerol) do not generally dissociate when placed in aqueous solution. Which of the following solutions would be expected to contain the greatest number of solute particles (molecules or ions)?

#Question id: 19493

#Unit 4. Cell Communication and Cell Signaling

#Question id: 1538

#Unit 4. Cell Communication and Cell Signaling

Many aspects of the biology of stem cells, including maintenance of pluripotency, self-renewal, and differentiation, are controlled by the phenomenon of RNA interference involving a variety of small molecules of RNA.

Match the following miRNA (Column I) with their target gene (Column II).

#Question id: 1252

#Unit 4. Cell Communication and Cell Signaling

 Following statements are regarding to the phosphoinositide signaling pathway.

A. Many RTKs and cytokine receptors can initiate the IP3/ DAG signaling pathway by activating phospholipase Cβ (PLCβ), a different PLC isoform.

B. Activated RTKs and cytokine receptors also can initiate another phosphoinositide pathway by binding a PI-3 kinase, thereby allowing the enzyme access to its membrane-bound phosphoinositide substrates, which then become phosphorylated at the 3 position.

C. Protein kinase B (PKB) becomes partially activated by binding to PI 3-phosphates with its PH domain.

D. Full activation of PKB requires phosphorylation by the kinase PDK1, which is also recruited to the membrane by binding to PI 3-kinase, and by a second kinase, PDK2.

Which of the following combination is incorrect?

#Question id: 12517

#Unit 6. System Physiology – Plant