The classic work of Christian Anfinsen in the 1950s on the enzyme ribonuclease revealed the relation between the amino acid sequence of a protein and its conformation. Ribonuclease is a single polypeptide chain consisting of 124 amino acid residues cross-linked by four disulfide bonds. Anfinsen’s plan was to destroy the three-dimensional structure of the enzyme and to then determine what conditions were required to restore the structure.

The critical observation of Anfinsen that the denatured ribonuclease, freed of urea and b -mercaptoethanol by dialysis;

I. The sulfhydryl groups of the denatured enzyme became reduced by air, and the enzyme spontaneously refolded into a catalytically active form.

II. These experiments showed that the information needed to specify the catalytically active structure of ribonuclease is contained in its amino acid sequence.

III. The 105 wrong pairings have been picturesquely termed “scrambled” ribonuclease.

IV. He found that scrambled ribonuclease spontaneously converted into fully active, native ribonuclease when trace amounts of b -mercaptoethanol were added to an aqueous solution of the protein.

Choose incorrect options;

#Question id: 23830

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#Question id: 12559

#Unit 7. System Physiology – Animal

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#Unit 4. Cell Communication and Cell Signaling

What signal is released by endothelial cells to recruit circulating leukocytes?

#Question id: 1257

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to protein kinase A which phosphorylates multiple intracellular target proteins expressed in different cell types.

A. Inactive PKA is a tetramer consisting of two regulatory (R) subunits and two catalytic (C) subunits.

B. Each R subunit contains a pseudo-substrate domain whose sequence resembles that of a peptide substrate and binds to the active site in the catalytic domain but is not phosphorylated; thus the pseudo-substrate domain inhibits the activity of the catalytic subunits.

C. active PKA is turned off by binding of cAMP Each R subunit has two distinct cAMP-binding sites, called CNB-A and CNB-B.

D. Binding of cAMP by an R subunit of PKA occurs in a cooperative fashion; that is, binding of the first cAMP molecule to CNB-B increases the Kd for binding of the second cAMP to CNB-A. Thus small changes in the level of cytosolic cAMP can cause proportionately large changes in the number of dissociated C subunits and, hence, in cellular kinase activity.

Which of the following statements are incorrect?