Fed and Fasting State Flashcards
What will the excess carbohydrate be used for inside the cell?
After carbohydrate is no longer needed for energy production the excess glucose will be converted into the storage molecule glycogen.
Glycogen is stored in the liver and muscle.
Excess glucose is converted into glycogen vis glycogenesis.
Each glycogenesis cycle adds one extra glucose unit onto the growing chain.
What will excess lipid be used for?
Excess lipid is not needed to generate ATP so it will be stored in the adipose tissue and liver as Triacylglycerol (TAG).
When lipid is required as the energy source (in the fasting state), the TAG can be broken down into its individual components (3 fatty acids and one glycerol), which are then metabolised by different metabolic reactions to generate ATP (fatty acid used in
beta-oxidation and glycerol used in glycolysis).
What will happen to the excess amino acids (breakdown product from the dietary protein)?
Amino acids that are not required to build new proteins for the cell will be broken down via amino acid metabolism.
This removes the nitrogen atoms within the AAs from the body. Too much nitrogen in the body is toxic.
The reactions required to remove the nitrogen atoms from an amino acid are transamination, followed by oxidative deamination and then the urea cycle.
The output of the urea cycle is urea. Urea is taken
to the kidneys via the blood to be removed via the urine.
Explain why lipid is the main source of ATP during the fasting state (rather than carbohydrate)?
What must happen to the stored triacylglycerol (TAG) before it can be used to generate ATP?
The body’s capacity to store lipid (in the adipose tissue) is much greater than its carbohydrate storage (glycogen stores), so there are more lipid reserves available in the fasting state to be metabolised to generate ATP.
Lipolysis occurs in the adipose tissue to release the fatty acids and glycerol from TAG.
The FAs are then taken to the cells and beta-oxidation converts it into many units of acetyl CoA.
Acetyl CoA is the input required to begin the CMP, as it is needed in the first step of the CAC.
Thus, for lipid to be used as a source of ATP, beta-oxidation is required to break the fatty acid down into many units of acetyl CoA.
How will an individual use the glycogen stored in the muscle and liver during the fasting state?
Is there a way that the glycogen can be used to generate ATP? Refer to the relevant metabolic
pathways.
When glucose becomes less available to produce ATP, the individual enters the fasting state.
Glycogen stores are broken down into individual glucose units through the glycogenolysis reaction.
Each glycogenolysis reaction removes one glucose
unit from the glycogen chain (up to 1,000,000) glucose units.
Before glycogen can be used to generate ATP, individual glucose units must be broken off the glycogen chain and are then used in glycolysis to create pyruvate.
Pyruvate is converted to acetyl CoA in preparation for the CAC, which is the first step in the CMP.
After completing the CMP, a lot of ATP are generated.
How will the individual manage to maintain a normal blood glucose level to ensure enough glucose is available to be metabolised by the brain during the fasting state?
Refer to the relevant metabolic pathways (gluconeogenesis and glycogenolysis).
Blood glucose levels need to be maintained so that glucose in the blood can be trafficked to glucose-dependent organs such as the brain, where it is used to generate ATP.
Gluconeogenesis is a metabolic process used to create glucose in times where carbohydrate intake is low (such as the fasting state). This is where pyruvate from a non-carbohydrate source (such as oxaloacetate and lactate) is converted into glucose.
Gluconeogenesis is almost the reverse of the glycolysis reaction, but there are some different enzymes required to facilitate certain reaction steps.
Glycogen stored in the liver can also be broken down into glucose units via glycogenolysis. Before the glucose can exit the cell, an enzyme only present in the liver cells removes a phosphate unit from the glucose, producing free glucose (no phosphate attached). The free glucose can then be taken out of the cell into the blood and assist in increasing the blood glucose level.
