The presence of the negatively-charged phosphate in the molecule also prevents the sugar from leaving the cell. When hexokinase is inhibited, glucose diffuses out of the cell and does not become a substrate for the respiration pathways in that tissue. The product of the hexokinase reaction is glucosephosphate, which accumulates when a later enzyme, phosphofructokinase, is inhibited. Glycolysis : The glycolysis pathway is primarily regulated at the three key enzymatic steps 1, 2, and 7 as indicated.
Note that the first two steps that are regulated occur early in the pathway and involve hydrolysis of ATP. Phosphofructokinase is the main enzyme controlled in glycolysis. An increase in citrate concentration can occur because of a blockage in the citric acid cycle. Fermentation, with its production of organic acids like lactic acid, frequently accounts for the increased acidity in a cell; however, the products of fermentation do not typically accumulate in cells.
The last step in glycolysis is catalyzed by pyruvate kinase. The pyruvate produced can proceed to be catabolized or converted into the amino acid alanine. If no more energy is needed and alanine is in adequate supply, the enzyme is inhibited. Recall that fructose-1,6-bisphosphate is an intermediate in the first half of glycolysis.
The regulation of pyruvate kinase involves phosphorylation, resulting in a less-active enzyme. Dephosphorylation by a phosphatase reactivates it.
Pyruvate kinase is also regulated by ATP a negative allosteric effect. If more energy is needed, more pyruvate will be converted into acetyl CoA through the action of pyruvate dehydrogenase. If either acetyl groups or NADH accumulate, there is less need for the reaction and the rate decreases.
Pyruvate dehydrogenase is also regulated by phosphorylation: a kinase phosphorylates it to form an inactive enzyme, and a phosphatase reactivates it. The kinase and the phosphatase are also regulated. The citric acid cycle is controlled through the enzymes that catalyze the reactions that make the first two molecules of NADH. Specific enzymes of the electron transport chain are unaffected by feedback inhibition, but the rate of electron transport through the pathway is affected by the levels of ADP and ATP.
Privacy Policy. Skip to main content. Cellular Respiration. Search for:. Regulation of Cellular Respiration. Regulatory Mechanisms for Cellular Respiration Cellular respiration can be controlled at each stage of glucose metabolism through various regulatory mechanisms. Learning Objectives Explain the mechanisms that regulate cellular respiration.
Key Takeaways Key Points Varying forms of the GLUT protein control the passage of glucose into the cells of specific tissues, thereby regulating cellular respiration. Reactions that are catalyzed by only one enzyme can go to equilibrium, which can cause the reaction to stall. Label the diagram below of the activities occurring on the ECT. Complete the summary diagram of cellular respiration.
Page 5 of 7 Label the diagram of fermentation below: Does aerobic cellular respiration happen in prokaryotic organisms — if yes — where? What is the overall purpose of fermentation? Why does it have to occur? What is a facultative anaerobe? What is the evolutionary significance of glycolysis?
Also, glycolysis is the most widespread metabolic pathway, suggesting that it evolved very early in the history of life on earth. Page 6 of 7 Why do fats provide a little more than twice as many calories per gram as compared to carbohydrates or proteins? Hint: Think of the output of the Citric Acid Cycle.
Since the purpose of cellular respiration is to produce ATP, when a cell senses that it has lots of ATP, it will reduce the amount of cellular respiration it's performing. When a cell senses that it has lots of AMP it tells the cell that it's used up a lot of ATP and therefore needs to make more. Why would phosphofructokinase being allosteric in character be an advantage to the control of cellular respiration?
When there is too much of one thing then it will go slower, it gets backed up. When an enzyme gets caught up in a lot of work it works slower and inefficiently. So when there is already enough work an ATP will bind to the inhibiting site on the allosteric phosphofructokinase to signal that it can slow down glycolysis.
It helps cellular respiration because it allows it to go more smoothly and effectively. AMP works the opposite way by speeding it up. Page 7 of 7. Download advertisement. Add this document to collection s. You can add this document to your study collection s Sign in Available only to authorized users. Description optional. Visible to Everyone. Just me. Add this document to saved.
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