Protein disulfide isomerase (pdi) is a protein folding enzyme that catalyzes disulfide–sulfhydryl exchange reactions. ribonuclease is an enzyme with two β-sheets, three α-helices, and four disulfide bridges critical to the stability of its structure. pdi rapidly converts inactive, scrambled ribonuclease to enzymatically active ribonuclease. this process is driven by the decrease in free energy as the scrambled conformations are converted into the stable, active conformation of the enzyme. in contrast, pdi rapidly inactivates insulin. what does pdi's effect on insulin imply about the structure of insulin? the three‑dimensional shape of insulin does not contain any disulfide bonds. the active conformation of insulin has more β-sheets than α-helices. the amino acid sequence of insulin is similar to the amino acid sequence of ribonuclease. the active conformation of insulin is not the most thermodynamically preferred form.

Read the following scenario to answer the following question. over the past 60 years, many amphibian species have experienced significant population declines, and some species have become extinct. scientists suspected that local human activities such as the destruction of wetlands, regional pollution, and deforestation were the main reasons for these losses. however, research over the past 20 years reveals significant amphibian population declines in protected areas of the world, such as nature preserves and parks. these global declines suggest widespread problems including increased ultraviolet radiation, acid rain, and disease. in switzerland, for example, 14 of the 20 native amphibian species are threatened with extinction. when most populations of a wide-ranging amphibian species are lost and the few remaining populations are widely separated, we expect to see that a. the founder effect becomes increasingly important b. microevolution no longer occurs c. gene flow between populations is reduced d. artificial selection becomes a greater factor in microevolution

The empty trna moves off and picks up another matching amino acid from the cytoplasm in the cell. the anticodon of the trna, with its attached amino acid, pairs to the codon of the mrna, which is attached to a ribosome. this sequence is repeated until the ribosome reaches a stop codon on the mrna, which signals the end of protein synthesis. the ribosome forms a peptide bond between the amino acids, and an amino acid chain begins to form. when a second trna with its specific amino acid pairs to the next codon in sequence, the attached amino acid breaks from the first trna and is bonded to the amino acid of the second trna.

Which zone within the open-ocean zone is home to the most organisms? deep zone surface zone intertidal zone transition zone