1.
Which of the following occurs in an individual at rest who has fasted for 12 hours?
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Correct Answer
D. Phosphorus, pyruvate kinase and glycogen synthase are phosphorylated in liver
Explanation
During a 12-hour fast, the body needs to maintain glucose levels to provide energy. Gluconeogenesis is the process by which glucose is produced from non-carbohydrate sources, such as amino acids and fatty acids. This process occurs in the liver. Phosphorylation is a chemical process in which a phosphate group is added to a molecule, and it plays a crucial role in regulating enzyme activity. In the liver, during fasting, phosphorus, pyruvate kinase, and glycogen synthase are phosphorylated. This phosphorylation helps to inhibit glycogen synthesis and promote gluconeogenesis, ensuring a steady supply of glucose for energy production.
2.
What takes place during the conversion of pyruvate to glucose during glyconeogenesis?
Correct Answer
A. Biotin is required
Explanation
During the conversion of pyruvate to glucose during glyconeogenesis, biotin is required. Biotin is a coenzyme that plays a crucial role in the carboxylation reactions involved in the conversion process. It acts as a carrier of activated carbon dioxide (CO2) and transfers it to pyruvate, resulting in the formation of oxaloacetate. This oxaloacetate is then converted into glucose through a series of enzymatic reactions. Therefore, biotin is necessary for the successful conversion of pyruvate to glucose during glyconeogenesis.
3.
What can a high ratio of insulin to glucagon do?
Correct Answer
C. Promote synthesis of Glycogen
Explanation
A high ratio of insulin to glucagon can promote the synthesis of glycogen. Insulin stimulates the uptake of glucose by cells and promotes the conversion of glucose into glycogen, which is stored in the liver and muscles for later use. Glucagon, on the other hand, promotes the breakdown of glycogen into glucose, increasing blood sugar levels. Therefore, when there is a high ratio of insulin to glucagon, it indicates a state where insulin is dominant, leading to an increase in glycogen synthesis. This is commonly observed during the fed state when blood glucose levels are high.
4.
Which of the following substrate cannot contribute to net gluconeogenesis in mammalian liver?
Correct Answer
A. Palmitate
Explanation
Palmitate cannot contribute to net gluconeogenesis in mammalian liver because it is a fatty acid, and fatty acids cannot be converted into glucose through gluconeogenesis. Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources, such as amino acids and glycerol, but fatty acids cannot be converted into glucose. Therefore, palmitate cannot be used as a substrate for gluconeogenesis in the mammalian liver.
5.
What is the enzyme used in both glycolysis and gluconeogenesis?
Correct Answer
A. 3-phosphoglycerate kinase
Explanation
3-phosphoglycerate kinase is the correct answer because it is an enzyme that is involved in both glycolysis and gluconeogenesis. In glycolysis, 3-phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, generating ATP. In gluconeogenesis, it catalyzes the reverse reaction, converting 3-phosphoglycerate to 1,3-bisphosphoglycerate. This enzyme plays a crucial role in both pathways, facilitating the interconversion of metabolites and the production of ATP.
6.
What is Gluconeogenesis useful for?
Correct Answer
C. Regulating Blood glucose level
Explanation
Gluconeogenesis is the process by which the body produces glucose from non-carbohydrate sources, such as amino acids and glycerol. This process is important for maintaining blood glucose levels within a normal range, especially during periods of fasting or low carbohydrate intake. By producing glucose, gluconeogenesis helps to ensure that there is a constant supply of fuel for the brain and other organs that rely on glucose as their primary energy source. Therefore, it is useful for regulating blood glucose levels in the body.
7.
What generates glucose in gluconeogenesis?
Correct Answer
C. Non carbohydrate carbon substrates
Explanation
Gluconeogenesis is a metabolic pathway that involves the synthesis of glucose from non-carbohydrate carbon substrates, such as amino acids, lactate, and glycerol. These substrates can be converted into glucose through a series of enzymatic reactions in the liver and kidneys. Sucrose, yeast, and carbohydrate carbon substrates do not directly generate glucose in gluconeogenesis.
8.
What are main gluconeogenic precursors (in humans)?
Correct Answer
D. All of the above
Explanation
The main gluconeogenic precursors in humans are lactate, alanine, and glycerol. Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate sources. Lactate is produced during anaerobic metabolism, alanine is derived from the breakdown of amino acids, and glycerol is obtained from the breakdown of triglycerides. All three of these precursors can be converted into glucose through various enzymatic reactions, making them important contributors to maintaining blood glucose levels.
9.
Which of the following is Gluconeogenesis often associated with?
Correct Answer
D. Ketosis
Explanation
Gluconeogenesis is a metabolic pathway that involves the synthesis of glucose from non-carbohydrate sources such as amino acids, lactate, and glycerol. It is often associated with ketosis, a metabolic state in which the body produces ketones as a result of using fat for fuel instead of glucose. During ketosis, the body's glucose levels are low, and gluconeogenesis helps to maintain blood sugar levels by producing glucose from non-carbohydrate sources. Therefore, gluconeogenesis is often associated with ketosis.
10.
Where does gluconeogenesis take place in vertebrates?
Correct Answer
A. Liver
Explanation
Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources. It occurs mainly in the liver, which has the necessary enzymes and metabolic pathways to carry out this process efficiently. The liver plays a central role in maintaining blood glucose levels by producing glucose when the body needs it, such as during fasting or low carbohydrate intake. The heart, stomach, and intestine do not have the same capacity for gluconeogenesis as the liver, making the liver the primary site for this metabolic pathway in vertebrates.