metabolic integration Flashcards
(29 cards)
Why is metabolic control during a low-carbohydrate diet similar to the early stages of starvation?
Because both involve limited glucose availability, the body increases gluconeogenesis to supply glucose primarily for the CNS and red blood cells, while most tissues shift to using fatty acids and ketone bodies for energy. The CNS adapts by gradually using ketones, but RBCs rely solely on glucose, so the body prioritizes maintaining glucose supply for these cells.
what are isoenzymes
Enzymes that catalyse the same biochemical reaction
How does the insulin/glucagon ratio affect lipolysis in adipose tissue?
A low insulin/glucagon ratio activates lipolysis in adipose tissue cells, promoting the breakdown of stored fat into free fatty acids and glycerol for energy.
What effect does a high insulin/glucagon ratio have on lipogenesis in the liver?
A high insulin/glucagon ratio activates lipogenesis in the liver, promoting fat synthesis and storage.
When are insulin-dependent glucose transporters (like GLUT4) recruited to the cell membrane?
Insulin-dependent glucose transporters are recruited to the cell membrane when insulin levels are high, facilitating glucose uptake into muscle and adipose tissue.
What happens to lipolysis in muscle and adipose tissue when insulin levels are high?
High insulin levels inhibit lipolysis in muscle and adipose tissue, favoring energy storage rather than breakdown.
Which type of metabolic fuel is utilised for generating glucose under conditions of severe starvation?
amino acids
How does brain metabolism adapt during prolonged starvation?
Up to half of the brain’s energy requirement can be met by ketone bodies, which serve as an alternative fuel to glucose during prolonged starvation.
Can the brain use fatty acids directly for energy?
No, the brain cannot use fatty acids directly because they do not cross the blood-brain barrier effectively.
What is the primary fuel for the brain under normal conditions?
Under normal conditions, glucose is the primary fuel for the brain.
Why can liver glycogen provide glucose to other tissues during fasting, but muscle glycogen cannot?
Because muscle cells lack glucose-6-phosphatase, they cannot convert glycogen-derived glucose-6-phosphate into free glucose for release; liver cells have this enzyme and can release glucose into the bloodstream.
Are metabolic pathways generally regulated, and how is this regulation achieved?
Most metabolic pathways are regulated through various mechanisms, including allosteric control, covalent modifications, changes in enzyme levels, and hormonal signals to maintain cellular balance.
Does regulation of metabolic pathways always involve changing the amount of enzymes?
No, regulation can occur through rapid mechanisms like allosteric modulation or covalent modifications without changing enzyme amounts.
Is hormonal control the only way metabolic pathways are regulated?
No, metabolic pathways can be regulated by hormones as well as by substrate availability, allosteric effectors, and covalent enzyme modifications.
What substrate do erythrocytes use to generate ATP during the early stages of starvation?
glucose exclusively to generate ATP because they lack mitochondria and cannot metabolize fatty acids or ketone bodies.
Why can erythrocytes not use fatty acids or ketone bodies for energy?
Because erythrocytes lack mitochondria, they cannot carry out oxidative metabolism and rely solely on anaerobic glycolysis using glucose
Can fatty acids be converted into glucose during starvation?
No, fatty acids cannot be converted into glucose because their breakdown yields acetyl-CoA, which cannot serve as a gluconeogenic substrate.
What hormone is released from the pancreas in response to increased blood glucose levels after a meal?
insulin is released from the pancreas to promote glucose uptake by cells and lower blood glucose levels.
What hormone is released by the pancreas when blood glucose levels are low?
Glucagon is released to stimulate glucose production and increase blood glucose levels.
What is a zymogen?
A zymogen is the inactive form of an essential enzyme that requires activation (often by proteolytic cleavage) to become active.
Why are enzymes sometimes produced as zymogens?
To prevent them from digesting proteins in the cells where they are made, ensuring they become active only in the proper location.
How is metabolic control typically exerted in reversible metabolic pathways?
Control is exerted at irreversible steps in the pathway, which serve as key regulatory points to direct and regulate the pathway’s flow.
What happens in the body when there is an excess of carbohydrate intake?
The pancreas releases insulin, promoting glucose storage as glycogen in the liver and muscles. Once glycogen stores are full, liver cells convert glucose into acetyl-CoA via glycolysis and the PDH reaction, which is then used for fatty acid synthesis. These fatty acids are exported as triacylglycerols (TAGs) in VLDLs to adipose tissue for storage.
Which two hormones inhibit food intake?
PYY3-36 and insulin inhibit food intake by signaling satiety and reducing appetite.
