1. Integrated metabolism A. A molecule of glucose that you eat can eventually be
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Question
1. Integrated metabolism
A. A molecule of glucose that you eat can eventually be transformed into part of a fatty acid that you store. Circle the pathways/cycles below that are part of this overall flow of carbon atoms. Cross out any that are not.
Gluconeogenesis, beta-oxidation, citric acid cycle, glycolysis, urea cycle, fatty acid synthesis
B. Trace the metabolic path of this glucose molecule through the enzymes it encounters along the way to being made into fat. Write all the enzymes in the list below into the proper places in the figure below. If the enzyme is not used, write its name in a “not used" column. If it is used, write the enzyme in the order that the carbon atoms from glucose encounter the enzymes.
Pyruvate dehydrogenase, fumarase, aldolase, lactate dehydrogenase, pyruvate kinase, acetyl CoA carboxylase, fatty acid synthase, hexokinase, carnitine acyltransferase, ATP synthase
B. What is the minimum number of glucose molecules that would be necessary to be the carbon source for synthesis of a 16-carbon fatty acid through this pathway?
C. How many net glucose can be made from one molecule of a 16-carbon fatty acid?
2. Describe each cycle/transport system (compounds, compartments, tissues) and explain its purpose:
A. citrate transport system
B. Cori cycle
C. glucose/alanine cycle
3.
Explain the logic of these pathway regulations:
A. Phosphofructokinase, not hexokinase, is the main regulation site of glycolysis.
B. SuccinylCoA inhibits the entry of acetyl CoA into the citric acid cycle.
C. NADH inhibits pyruvate dehydrogenase.
D. Citrate inhibits the citric acid cycle and activates acetyl-CoA carboxylase.
E. Insulin leads to activation of glycogen synthase.
Explanation / Answer
A. A molecule of glucose enters the process of GLYCOLYSIS to breakdown into pyruvic acid. This pyruvic acid changes into acetyl coA which in turn enters the citric acid cycle to generate carbon dioxide and ATP. When acetyl coA is in excess it enters into the process of lipogenesis i.e. FATTY ACID SYNTHESIS. Gluconeogenesis on the other hand is a process which results in generation of glucose from non carbohydrate source. Beta oxidation of fatty acid is a process where fatty acid molecules are broken down to generate acetyl coA which can enter citric acid cycle. Urea cycle or ornithine cycle produces urea from ammonia.
The enzymes which takes part in the process of glycolysis are hexokinase which converts glucose to glucose 6 phosphate. This G6P through intermediate products form fructose 1,6 bisphosphate which gets converted into dihydroxy acetone phosphate and glyceraldehyde 3 phosphate by the action of the enzyme aldolase. These products ultimately form phosphoenolpyruvate which changes into pyruvic acid by the action of pyruvate kinase. This pyruvate kinase changes into acetyl coA by the action of pyruvate dehydrogenase. Acetyl coA changes into malonyl coA by the action of acetyl coA carboxylase. Both acetyl coA and malonyl coA changes into palmitate by the help of the enzyme fatty acid synthase in the presrnce of NADPH. ATP synthase acts like an ion pump to generate ATP which is a key component in any metabolic pathway. The other enzymes, fumarase helps in citric acid cycle where fumarate changes into malate. Lactate dehydrogenase helps in conversion of pyruvic acid to lactic acid. Carnitine acyl transferase helps in beta oxidation of fatty acid.
1molecule of palmitic acid which has 16 carbon requires 8 molecules of acetyl coA. 1 glucose breaks down into 2 acetyl coA, so 4 glucose is required for 8 acetyl coA molecules.
Similarly a 16carbon long fatty acid breaks down into 8 molecules of acetyl coA which can enter Cori cycle to generate 4 glucose molecules.
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