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Chapter 12: Problem 13

In many tissues, one of the earliest responses to cellular injury is a rapid increase in the levels of enzymes in the pentose phosphate pathway. Ten days after an injury, heart tissue has levels of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase that are 20 to 30 times higher than normal, whereas the levels of glycolytic enzymes are only \(10 \%\) to \(20 \%\) of normal. Suggest an explanation for this phenomenon.

Short Answer

Expert verified
In response to injury, cells increase the activity of the pentose phosphate pathway to support repair mechanisms and growth by synthesizing nucleotides and nucleic acids. This makes the levels of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase increase. Conversely, the glycolysis process and thus the levels of its enzymes are downregulated as resources are redirected from energy conservation to repair the injury.

Step by step solution

01

Understanding the Pentose Phosphate Pathway

The pentose phosphate pathway is a metabolic process that provides the cells with ribose 5-phosphate for the synthesis of nucleotides and nucleic acids, and NADPH for biosynthesis reactions. The main enzymes involved in the pathway are glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.
02

Role of Pentose Phosphate Pathway in Cellular Responses to Injury

When a cell is injured, it requires repair mechanisms to restore normal function. This involves increased production of nucleotides and nucleic acids to replace damaged molecules and support cell growth, which necessitates an upshift in the activity of the pentose phosphate pathway, thus the level of its enzymes, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, rise notably.
03

Understanding Glycolysis

Glycolysis is a metabolic process involving the conversion of glucose into pyruvate, yielding ATP for energy. When cells are injured, energy conserving processes like glycolysis are oftentimes downregulated as the cell redirects resources to repairing damage, leading to a reduction in the levels of glycolytic enzymes.
04

Putting It All Together

Therefore, the higher levels of enzymes from the pentose phosphate pathway after injury can be explained by the cell's need for repair mechanisms and increased nucleotides production, and the lower levels of glycolytic enzymes can be explained by redirection of cell resources to damage repair process rather than energy production.

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Most popular questions from this chapter

The polypeptide hormone glucagon is released from the pancreas in response to low blood glucose levels. In liver cells, glucagon plays a major role in regulating the rates of the opposing glycolysis and gluconeogenesis pathways by influencing the concentrations of fructose 2,6 bisphosphate (F2,6 BP). If glucagon causes a decrease in the concentrations of F2,6 BP, how does this result in an increase in blood glucose levels?

Epinephrine promotes the utilization of stored glycogen for glycolysis and ATP production in muscles. How does epinephrine promote the use of liver glycogen stores for generating the energy needed by contracting muscles?

(a) Draw the structures of the reactants and products for the second reaction catalyzed by transketolase in the pentose phosphate pathway. Show which carbons are transferred. (b) When \(2-\left[{ }^{14} \mathrm{C}\right]\)-glucose 6-phosphate enters the pathway, which atom of fructose 6-phosphate produced by the reaction in Part (a) is labeled? (c) When \(2-\left[{ }^{14} \mathrm{C}\right]\)-glucose 6-phosphate enters the pathway, which atom of fructose 6-phosphate produced by the transaldolase reaction is labeled?

What important products of the citric acid cycle are required for gluconeogenesis from pyruvate?

The pentose phosphate pathway and the glycolytic pathway are interdependent, since they have in common several metabolites whose concentrations affect the rates of enzymes in both pathways. Which metabolites are common to both pathways?
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