Definitions and Functions
What is gluconeogenesis for?
To synthesize glucose from non-carbohydrate compounds, especially under conditions of carbohydrate deficiency.
Which enzyme starts the process of glycogenesis by adding a phosphate group to glucose?
glucokinase
What molecules begin gluconeogenesis?
pyruvate, lactate, or amino acids.
Which hormone stimulates glycogenesis in excess glucose?
Insulin
How is glycogen utilized during exercise?
Glycogen in muscle is broken down through the process of glycogenolysis, providing energy to the cells
In which organ do both of these processes occur?
In the liver
Which enzyme elongates the glycogen chain?
glycogen synthase
What occurs in the smooth endoplasmic reticulum during gluconeogenesis?
glucose-6-phosphate is converted to glucose
How does epinephrine affect glycogenesis?
Suppresses glycogenesis and promotes the breakdown of glycogen to release energy.
What happens to blood glucose levels during fasting?
Blood glucose levels drop and gluconeogenesis is activated to maintain normal glucose levels
Name the primary function of glycogenesis
Storing energy in the form of glycogen for later use.
Which enzyme is involved in the conversion of fructose-1,6-bP to fructose-6-P?
Fructose-1,6-phosphatase
What changes occur to glucose during the initial stages of glycogenesis?
A phosphate group is added to glucose and it is converted to UDP-glucose.
Under what conditions does the process of gluconeogenesis begin?
under glucose deficiency or starvation conditions
Why is the process of gluconeogenesis important in diabetes?
In diabetes, glucose regulation is impaired and gluconeogenesis helps maintain normal blood sugar levels
Compare the main function of gluconeogenesis and glycogenesis
Gluconeogenesis synthesizes glucose from non-carbohydrate sources and glycogenolysis breaks down glycogen to release glucose.
After conversion of oxaloacetate to PEP, which enzymes are involved in completing gluconeogenesis?
Fructose-1,6-bisphosphatase and glucose-6-phosphatase
Why does gluconeogenesis require more energy than glycolysis?
It goes in the opposite direction, requires additional enzymes and the use of ATP/GTP molecules
How does the ratio of ATP to AMP affect gluconeogenesis?
High level of ATP (and low level of AMP) stimulates gluconeogenesis, low level of ATP (and high level of AMP) inhibit it.
Athletes use "carbohydrate loading", this is eating carbohydrates before workouts. Explain why they do this using knowledge of glycogenesis
Cells store maximum glycogen, which can later be used for energy
Why is glycogen stored in the body instead of free glucose?
Glycogen takes up less space, requires less water, and does not increase the osmotic pressure in the cell.
What function does the enzyme glucose-6-phosphatase perform in gluconeogenesis?
Converts glucose-6-phosphate into free glucose that can leave the cell
Describe the entire pathway of conversion of pyruvate to PEP (can be done without enzymes)
- Pyruvate is converted to oxaloacetate (by pyruvate carboxylase).
- Oxaloacetate is converted to malate (malate dehydrogenase) and released into the cytoplasm.
- In the cytoplasm, malate is converted back to oxaloacetate (malate dehydrogenase).
- oxaloacetate is converted to PEP (PEP-carboxykinase)
What molecules can block the process of gluconeogenesis?
AMP and fructose-2,6-bisphosphate can inhibit key enzymes of gluconeogenesis
How does gluconeogenesis help the body during prolonged fasting?
gluconeogenesis provides the body with needed glucose from reserve sources such as amino acids and glycerol in the absence of food