In gluconeogenesis, the pyruvate to phosphoenolpyruvate is one of the bypass steps that is different from...

In gluconeogenesis, the pyruvate to phosphoenolpyruvate is one of the bypass steps that is different from the reverse reaction in glycolysis due to the irreversible nature of pyruvate kinase. There are two pathways for this bypass reaction that differ in the location where the final PEP product is synthesized – either in the mitochondria or in the cytoplasm. Assume that your cell is undergoing gluconeogenesis using pyruvate derived from the deamination of serine by the enzyme serine dehydratase:
L-serine → Pyruvate + NH3
Which of the two pathways of phosphoenolpyruvate synthesis will be used and why? What are the intermediate steps for this reaction, and where do they occur?

Expert Solution

L-serine → Pyruvate + NH3

This reaction occurs in liver cell cytoplasm. the pyruvate produced will undergo gluconeogenesis. It is transported to mitochondrial matrix. There it undergoes following reactions.

1. the pyruvate is converted to oxaloacetate by pyruvate carboxylase (mitochondria)

2. Oxaloacetate is converted to malate by malate dehydrogenas an enzyme present both in cytosol and mitochondria. This reaction occurs because mitochondrial membrane is impermeable to oxaloacetate but permeable to malate.

3. Malate is transported to cytosol and again converted to Oxalo acetate by same malate dehrydogenase.

4. Malate is converted to PEP by PEPcarboxy kinase. (cytosol)

5.PEP enters into gluconeogenesis.

Note: In cells which have PEPcarboxy kinase in mitochondria directly oxaloacetate is converted to PEP and transported to cytosol and enter gluconeogenesis.

gladiator answered 2 years ago

In the first by-pass step of gluconeogenesis, the conversion of pyruvate to phosphoenolpyruvate, pyruvate is carboxylated...

In the first by-pass step of gluconeogenesis, the conversion of pyruvate to phosphoenolpyruvate, pyruvate is carboxylated by pyruvate carboxylase to oxaloacetate, which is subsequently decarboxylated by PEP carboxykinase to yield phosphoenolpyruvate. Explain using thermodynamic terms why this by-pass step is necessary. Why couldn't the glycolytic enzyme responsible for interconverting phosphoenolpyruvate and pyruvate also participate in the gluconeogenesis pathway?

What four enzyme activities unique to gluconeogenesis are needed to bypass the three irreversible steps of...

What four enzyme activities unique to gluconeogenesis are needed to bypass the three irreversible steps of glycolysis. Draw the reactions catalyzed by these four enzymes.

Gluconeogenesis is generally the reverse of the glycolytic pathway, producing glucose from pyruvate. Some tissues cannot...

Gluconeogenesis is generally the reverse of the glycolytic pathway, producing glucose from pyruvate. Some tissues cannot survive without a source of glucose, and this is a way to produce glucose from other food molecules. (A) 7 reactions in glycolysis are used in the reverse direction in gluconeogenesis. How can this be?

What enzymes are necessary in gluconeogenesis to bypass the irreversible enzymes in glycolysis and what is...

What enzymes are necessary in gluconeogenesis to bypass the irreversible enzymes in glycolysis and what is the basic reaction they are catalyzing? How is their activity regulated, so glycolysis and gluconeogenesis are not occurring simultaneously?What tissues convert lactate back to pyruvate, which can then enter the citric acid cycle?

A heterotrophic cell encodes both the Pyruvate Carboxylase enzyme and the enzymes of the Glyoxylate Bypass....

A heterotrophic cell encodes both the Pyruvate Carboxylase enzyme and the enzymes of the Glyoxylate Bypass. Contrast the reactions leading to oxaloacetate via both mechanisms, starting with PEP. In environments with low organic carbon, which reaction(s) would be favored for carrying out anaplerosis and why?

In gluconeogenesis, pyruvate is converted to PEP in two reactions. These reactions include an initial carboxylation...

In gluconeogenesis, pyruvate is converted to PEP in two reactions. These reactions include an initial carboxylation followed by a decarboxylation in the second reaction. Based on these two reactions, you would assume that if radio-labeled 14CO2 was present in the reactions, it would not be incorporated into PEP. However, when 14CO2 is present with rat liver cells 14C slowly begins to appear in PEP and eventually on carbons 3 and 4 of glucose. Diagram a series of reactions that would...

4. a. Which steps in gluconeogenesis DO NOT occur in the cytoplasm? b. Gluconeogenesis can synthesize...

4. a. Which steps in gluconeogenesis DO NOT occur in the cytoplasm? b. Gluconeogenesis can synthesize glucose because it is energetically favorable in the cell. It is energetically favorable because it bypasses the three irreversible steps of glycolysis. Which enzymes in gluconeogenesis are involved in bypass these irreversible reactions? c. Fructose 2,6-bisphosphate (F-2,6-BP) helps regulate both glycolysis and gluconeogenesis. F- 2,6-BP levels are determined by a single polypeptide containing both phosphofructokinase 2 (PFK2) and fructose bisphosphatase 2 (FBPase2). How is...

5.Consider the regulation of glycolysis, gluconeogenesis, pyruvate dehydrogenase, and the TCA cycle, how is the regulation...

5.Consider the regulation of glycolysis, gluconeogenesis, pyruvate dehydrogenase, and the TCA cycle, how is the regulation of these pathways linked to thermodynamics? How are they linked to one another?

Briefly explain the steps by which the pyruvate dehydrogenase complex converts pyruvate to acetyl CoA and...

Briefly explain the steps by which the pyruvate dehydrogenase complex converts pyruvate to acetyl CoA and deposits it in the mitochondrial matrix. What cofactors are used, what are the products formed? How is the complex activity regulated?

Case 1: Pyruvate Kinase (PK) catalyzes the rate-limiting, ATP-generating step of glycolysis in which phosphoenolpyruvate (PEP)...

Case 1: Pyruvate Kinase (PK) catalyzes the rate-limiting, ATP-generating step of glycolysis in which phosphoenolpyruvate (PEP) is converted to pyruvate. Multiple isoenzymes of pyruvate kinase exist in mammals: type L, which is found in the liver and kidneys; type R, which is expressed in erythrocytes; type M1, which is found in tissues such as muscle and brain; and type M2, which is present in self-renewing cells such as embryonic and adult stem cells. 1) Under normal conditions, describe all the...

Question