Question

 

7.Discuss the physiological events occurring relative to fatty acid and carbohydrate metabolism when carbohydrate is scarce.

8.Describe the regulation of carbohydrate and lipid metabolism in terms of hormonal regulation. In your discussion, include the cell-signaling pathway(s) involved (including any secondary messengers that are involved).

Answer 1

Carbohydrates are the major macromolecules used by the body to release energy in form of ATP for its activities, through a process called cellular respiration.

Glucose formed by the metabolisam of carbohydrate are the main substrate for cellular respiration. When there is adepletion in the level of glucose cells use alternative pathways and substrates for liberation of energy.

1. Glycogenolysis: Glycogen is the stored form of glucose in the liver when there is a fall in the glucose level in the blood glycogen is converted into glucose. This process is called glycogenolysis. But glycogen reserves are limited hence body cannot depend on this pathway alone.

2. Gluconeogenesis : This is the formation of glucose from non carbohydrate molecules. This happens in the liver. Main substrate used for gluconeogenesis are amino acids and glycerol (part of tryglyceride molecule) .Certain cellular organs like brain can derive energy only from glucose as fatty acids cannot cross blood brain barrier. Hence gluconeogenesis is an important parthway during the depletion of blood Glucose. All amino acids cannot be broken down as they are building blocks of protein. Hence body depends on another molecule for enegy.

3. Fatty acid catabolisam : It is the breaking down of fatty acid also called oxidation of fatty acids. Fatty acids are broken down to from acetyl coA which enter the Crebs cycle, the end products latter passes through the Electron transport chain to release enegy. Few electron carriers are also produced during the breakdown of fatty acids which are also capable of releasing energy. However Fatty acids are not generally converted into glucose.

Fatty acid metabolisam: Fatty acids derived from the food are stored mainly in the adipose tisses and muscles. when there is a depletion of carbohydrate level in blood they are converted from storage forms to release energy. They are capable of releasing enormous amount of energy compared to other macromolecules. Fatty acid oxidation takes place in mitochondria and peroxisomes.

2. Hormonal control of carbohydrate and lipid metabolisam

Carbohydrate metabolisam : increasing level of glucose releases insulin from the beta cells,which reduces the glucose level in many ways.

1. INSULIN

Activate PFK 2 by phosphorylation , inturn activate Phosphofructo kinase 1 increasing the converstion of Fructose 6 phosphate into FRuctose 1,6 phosphate in the Glycolysis pathway leading to the breakdown of more glucose.

Increases	Decreases
Glycogenesis	lipolysis
Glycolysis	Gluconeogenesis
Protein synthesis	Gucogenolysis

2. GLUCAGON

when there is decrease in glucose level Glycogen is secreted. It activate G protein coupled receptor pathway and activate PKA. Glucagon binds to the receptor site activating the adenyly cyclase, activated into CAMP. which binds to the PKA. resulting release of catalytic site . The resultant kinase will phosphorylate bifunctional enzyme containing Phsosphofructo kinase2 and Fructose bisphosphatese 2. FB2 will be activated. Once activated it convert the Fructose 2,6 bisphosphate into Fructose 6 phosphate, which will form the substrate to make glucose through gluconeogenesis.

• It inhibit secretion of insulin
• increases glycogenolysis
• Increases gluconeogenesis
• Decrease protein synthesis
• Increase lypolysis

3. Epinephrine is released during emegency situvation from anterior medulla

It is antagonist to glucose hence increase the break down activities. It increases glycogenolysis, gluconeogenesis, increases lypolysis.

4.Glucocorticoids: cortisol

Act anatgonist to insulin. Increases the breakdown of glucose.