Question

Describe an example of each type of regulation in the context of glucose metabolism.

Factors That Determine Activity of Enzymes:

1) Extracellular signal

2) Transcription of specific genes

3) mRNA degradation

4) mRNA translation on ribosome

5) Protein degradation

6) enzyme sequestered in subcellular organelle

7) Enzyme binds substrate

8) Enzyme binds ligand

9) Enzyme undergoes phosphorylation/dephosphorylation

10) Enzyme combines with regulatory protein

Answer 1

ANSWER -

1. The hormones which plays an important role in glucose metabolism include Glucagon, Insulin, Glucose-dependent Inhibitory Peptide (GIP), Amylin and Glycogen-like Peptide-1 (GLP-1).
2. The hormone that increase the blood glucose levels is Glucagon and the hormones that reduce the blood glucose levels include Insulin, Glycogen like Peptide-1, GIP and Amylin. Blood glucose levels are enhanced by means of means of Glycogenolysis and Gluconeogenesis process in which Glycogen is broken down to its monomeric glucose units. In order to lower blood glucose levels, the process of Glycogenesis is carried out which is used to convert glucose to glycogen which is a polymeric unit of glucose which is stored post eating.
3. The condition in which there is low blood glucose levels is called as Hypoglycemia and the condition in which there is an enhanced level of glucose is called as Hyperglycemia.
4. Taking into consideration the regulation of glucose homeostasis, there is a closed loop mechanism which becomes functional in order to regulate glucose levels in the blood. It includes two hormones mainly the Glucagon and the Insulin both secreted from the pancreatic cells. After having a meal, there is subsequent absorption which occurs in the intestine followed by enhanced activity of the beta cells of pancreas to release Insulin to trigger Glycogenesis that is storage of glucose in the form of polymeric component called as Glycogen. When the blood glucose levels falls down due to the activity of Insulin and the inhibitory control over Glucagon, there will be release of Glucagon once the levels of Glucose falls down in the blood. This thus forms the closed loop.
5. The gene which encodes for the enzyme called as Phosphoenolpyruvate carboxykinase (PEPCK) plays a vital role in increasing blood glucose levels. It stimulates the formation of glucose or entry of glucose into blood as a process accompanying Glycogenolysis and Gluconeogenesis. Thus, this is the gene which is being positively controlled by the hormone Glucagon whereas negatively regulated by Insulin which inhibits its secretion. Another important gene mechanism which is being regulated is the one encoding for the enzyme Glucose-6-phosphatase which is involved in the cleavage of glucose-6-phosphate to release glucose and an inorganic phosphate group. This acts in accordance with the Glucagon hormone which enhances its transcriptional activity. Glycogen synthetase is an enzyme which actively participates in the process of formation of or synthesis of Glycogen and thus works in accordance with Insulin which has a positive effect on its activity and is being negatively regulated by Glucagon. Other important genes include the ones which codes for the Insulin receptors and Glucose transporter proteins. In the presence of Insulin, there is enhanced expression of Glut-4 receptors which leads to enhanced storage and entry of glucose into the hepatic cells leading to formation of glycogen residues. Insulin activity is basically mediated by the Insulin receptors which are synthesized only after a stimulatory signal initiated by uptake of glucose through food.

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