Intro to Gluconeogenesis: Study with Video Lessons, Practice Problems & Examples

Glucose can be obtained through dietary carbohydrates or synthesized via gluconeogenesis, particularly during low carbohydrate intake or fasting. This anabolic process, primarily occurring in the liver, converts non-carbohydrate sources like lactate, amino acids, and glycerol into glucose. Gluconeogenesis is essentially the reverse of glycolysis, bypassing irreversible steps with different enzymes when blood glucose levels are low. Understanding these metabolic pathways is crucial, as glucose is the primary energy source for the brain.

Intro to Gluconeogenesis Concept 1

Now, there are 2 ways that we could get glucose. One way is pretty obvious. We eat carbohydrates. A second way to make glucose is to synthesize it. And this is where gluconeogenesis comes into play. Now, gluconeogenesis is when your blood glucose is low, and we're gonna say, glucose is synthesized from non-carbohydrate sources for energy. Now here we're going to say this is most active when the diet is low in carbohydrates or in times of fasting. Now, this is incredibly important that we are able to synthesize glucose during these periods because glucose serves as the major energy source for our brain. Now, here, gluconeogenesis is an anabolic process that occurs mainly in the liver. And recall, anabolism involves reactions that use energy to build larger molecules from smaller molecules. If we take a look here at the liver, our non-carbohydrate sources we have as lactate and the amino acids. They can be converted to pyruvate, which in turn can be changed into DHAP (dihydroxyacetone phosphate) . From there, it can be transformed into the creation of glucose. We can also say that we have Glycerol as yet another way of converting it into DHAP and then towards making glucose. So, just remember, when it comes to glucose, there are 2 ways that we can get it. We can eat carbohydrates or we can synthesize them. In this case, synthesis means that we have to utilize gluconeogenesis.

Intro to Gluconeogenesis Concept 2

In this video, we'll talk about the difference between gluconeogenesis and glycolysis. Now, here we're going to say that gluconeogenesis can be viewed as the reverse of glycolysis with some exceptions. So remember, with glycolysis, we're starting out with glucose, we go through 10 reactions to get to 2 pyruvate molecules. In gluconeogenesis, we're going the other way. We're trying to create pyruvate through non-carbohydrate sources, and from pyruvate, we're trying to get back to glucose. Now here, recall that when it comes to glycolysis, we say reactions 1, 3, and 10 are irreversible. Now, gluconeogenesis bypasses these irreversible reactions by using different enzymes. These enzymes are upregulated whenever your blood glucose levels are low. So that's how we're able to bypass these irreversible processes that we've seen in glycolysis.

Intro to Gluconeogenesis Example 1

In this example question, it says, "Identify all the statements that are not true about gluconeogenesis." So, option A states, "Gluconeogenesis is the exact reverse of the glycolysis pathway." This statement is not true. It is not the exact reverse; there are some exceptions that occur. That's why this is not true. It is not an exact opposite or reverse, as there are some exceptions.

Gluconeogenesis primarily occurs in the liver cells. That is true. It is most active in times of fasting or starvation. This is also true. When your blood glucose levels are low, this process will kickstart the synthesis of glucose through gluconeogenesis.

Certain non-carbohydrates have to be converted to pyruvate before entering the gluconeogenesis pathway. Yes, certain non-carbohydrates, such as lactate and amino acids, must be converted into pyruvate, from pyruvate to dihydroxyacetone phosphate (DHAP) before they can eventually become glucose. So this last statement is true.

Out of our four statements, only option A is an incorrect or false statement. Here, gluconeogenesis is not the exact reverse of the glycolysis pathway, as it is the reverse with some exceptions that exist.

Here’s what students ask on this topic:

What is gluconeogenesis and why is it important?

Gluconeogenesis is the metabolic process by which glucose is synthesized from non-carbohydrate sources, such as lactate, amino acids, and glycerol. This process is crucial during periods of low carbohydrate intake or fasting, as it ensures a continuous supply of glucose, which is the primary energy source for the brain. Gluconeogenesis mainly occurs in the liver and is an anabolic process, meaning it uses energy to build larger molecules from smaller ones. Understanding gluconeogenesis is essential for comprehending how the body maintains blood glucose levels and energy balance, especially in situations where dietary glucose is not available.

How does gluconeogenesis differ from glycolysis?

Gluconeogenesis and glycolysis are essentially opposite processes. Glycolysis breaks down glucose into pyruvate through a series of 10 reactions, while gluconeogenesis synthesizes glucose from non-carbohydrate sources, starting with pyruvate. One key difference is that glycolysis includes three irreversible steps (reactions 1, 3, and 10), which gluconeogenesis bypasses using different enzymes. These enzymes are upregulated when blood glucose levels are low, allowing the body to produce glucose even when dietary intake is insufficient. Understanding these differences is crucial for grasping how the body regulates glucose levels under varying conditions.

What are the main non-carbohydrate sources used in gluconeogenesis?

The main non-carbohydrate sources used in gluconeogenesis are lactate, amino acids, and glycerol. Lactate is produced from anaerobic glycolysis in muscles and can be converted back to pyruvate. Amino acids, particularly alanine, can also be converted to pyruvate or other intermediates that feed into the gluconeogenesis pathway. Glycerol, derived from the breakdown of triglycerides, can be converted into dihydroxyacetone phosphate (DHAP), which is an intermediate in the pathway to glucose synthesis. These sources are crucial for maintaining blood glucose levels during fasting or low carbohydrate intake.

Where does gluconeogenesis primarily occur in the body?

Gluconeogenesis primarily occurs in the liver. The liver is well-equipped with the necessary enzymes and metabolic pathways to convert non-carbohydrate sources like lactate, amino acids, and glycerol into glucose. This process is vital for maintaining blood glucose levels, especially during periods of fasting or low carbohydrate intake. While the liver is the main site, the kidneys can also perform gluconeogenesis to a lesser extent. Understanding the liver's role in gluconeogenesis helps in comprehending how the body manages energy resources and maintains glucose homeostasis.

What enzymes are involved in bypassing the irreversible steps of glycolysis during gluconeogenesis?

During gluconeogenesis, specific enzymes are used to bypass the three irreversible steps of glycolysis. These enzymes include pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK) for bypassing the pyruvate kinase step, fructose-1,6-bisphosphatase for bypassing the phosphofructokinase-1 step, and glucose-6-phosphatase for bypassing the hexokinase/glucokinase step. These enzymes are upregulated when blood glucose levels are low, allowing the body to synthesize glucose from non-carbohydrate sources efficiently. Understanding these enzymes is crucial for grasping how gluconeogenesis operates and how it is regulated.