How does the folding of a protein chain affect enzyme function? Yeast in a close

Question

How does the folding of a protein chain affect enzyme function? Yeast in a closed container of grape juice consume sugar slowly as long as there is oxygen in the container. As soon as the oxygen is depleted, however, the rate of sugar consumption greatly increases. Why? Describe how the structure of DNA ensure its replication. How does the folding of a protein chain affect enzyme function? Yeast in a closed container of grape juice consume sugar slowly as long as there is oxygen in the container. As soon as the oxygen is depleted, however, the rate of sugar consumption greatly increases. Why? Describe how the structure of DNA ensure its replication. Yeast in a closed container of grape juice consume sugar slowly as long as there is oxygen in the container. As soon as the oxygen is depleted, however, the rate of sugar consumption greatly increases. Why? Describe how the structure of DNA ensure its replication.

Explanation / Answer

How does the folding of a protein chain affect enzyme function?

Enzymes and Protein Folding:
In addition to chaperones, which facilitate protein folding by binding to and stabilizing partially folded intermediates, cells contain at least two types of enzymes that catalyze protein folding by breaking and re-forming covalent bonds. The formation of disulfide bonds between cysteine residues is important in stabilizing the folded structures of many proteins (see Figure 2.16). Protein disulfide isomerase, which was discovered by Christian Anfinsen in 1963, catalyzes the breakage and re-formation of these bonds. For proteins that contain multiple cysteine residues, protein disulfide isomerase (PDI) plays an important role by promoting rapid exchanges between paired disulfides, thereby allowing the protein to attain the pattern of disulfide bonds that is compatible with its stably folded conformation. Disulfide bonds are generally restricted to secreted proteins and some membrane proteins because the cytosol contains reducing agents that maintain cysteine residues in their reduced (—SH form), thereby preventing the formation of disulfide (S—S) linkages.
The second enzyme that plays a role in protein folding catalyzes the isomerization of peptide bonds that involve proline residues. Proline is an unusual amino acid in that the equilibrium between the cis and trans conformations of peptide bonds that precede proline residues is only slightly in favor of the trans form. In contrast, peptide bonds between other amino acids are almost always in the trans form. Isomerization between the cis and trans configurations of prolyl peptide bonds, which could otherwise represent a rate-limiting step in protein folding, is catalyzed by the enzyme peptidyl prolyl isomerase. This enzyme is widely distributed in both prokaryotic and eukaryotic cells and can catalyze the refolding of at least some proteins.

2 Ans: The primary role of yeast is to convert the sugars present (namely glucose) in the grape must into alcohol. The yeast accomplishes this by utilizing glucose through a series of metabolic pathways that, in the presence of oxygen, produces not only large amounts of energy for the cell but also many different intermediates that the cell needs to function. In the absence of oxygen, the cell will continue some metabolic functions (such as glycolysis) but will rely on other pathways such as reduction of acetaldehyde into ethanol (fermentation) to "recharge" the co-enzymes needed to keep metabolism going. It is through this process of fermentation that ethanol is released by the yeast cells as a waste product. Eventually, if the yeast cells are healthy and fermentation is allowed to run to the completion, all fermentable sugars will be used up by the yeast with only the unfermentable pentose leaving behind a negligible amount of residual sugar.

Describe how the structure of DNA ensure its replication:

DNA Structure
DNA is a long molecule with a backbone of alternating sugar and phosphate groups. One of four nucleotide bases adenine (A), guanine (G), cytosine (C) and thymine (T) hangs off each sugar unit. The sequence of the four bases creates the genetic code for manufacturing proteins. The nucleotides of two DNA strands bind to each other to form the familiar double helix structure. The base pairing rules require that A only bind with T and C only bind with G. The cell must obey these pairing rules during replication to maintain accuracy and avoid mutations.
Replication
Replication is semi-conservative: newly replicated helices contain an original strand and a newly synthesized one. The original strand serves as a template for the creation of the new strand. Helicase enzymes unzip the double helix structure to expose the two template strands. The enzyme DNA polymerase is responsible for reading each nucleotide on a template strand and adding the complementary base on the elongating new strand. For example, when the polymerase encounters a G base on a template strand, it adds to the new strand a sugar-phosphate unit containing a C base.

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