Intro to Carbohydrate Metabolism - Online Tutor, Practice Problems & Exam Prep

The process of harvesting energy from carbohydrates begins with digestion, where food is mechanically and biochemically broken down. Salivary alpha amylase hydrolyzes starch and glycogen into smaller polysaccharides and maltose. In the stomach, this enzyme is inactivated, halting carbohydrate digestion. Further hydrolysis in the small intestine produces monosaccharides like glucose, fructose, and galactose. These monosaccharides enter metabolic pathways, including the citric acid cycle, generating ATP and electron carriers like NADH for oxidative phosphorylation, essential for energy production.

Intro To Carbohydrate Metabolism Concept 1

Hey everyone. So here we're going to say the process of harvesting energy from carbohydrates starts with digestion. Digestion itself is just the conversion of food to small molecules through mechanical and biochemical breakdown. Now when we say mechanical, we're referring to the chewing and grinding down of food into smaller molecules. Biochemical breakdown is just the use of hydrolysis to break down these larger molecules into smaller molecules.

Now in step a, we have our Salivary Alpha Amylase Enzyme. It hydrolyzes some starch and glycogen into smaller polysaccharides and maltose. Remember, polysaccharides are just polymers of glucose, so it's several glucose molecules connected by glycosidic linkages. Maltose represents a disaccharide, where we have 2 glucose molecules connected by a glycosidic linkage. Now here we're going to say that oligosaccharides are just are 3 to 10 monosaccharides connected together. They're produced through the hydrolysis of Glycogen and Starch and sometimes they're called dextrins.

Now, here our stomach acid inactivates salivary alpha amylase and halts carbohydrate digestion. The stomach itself does not release any enzymes in terms of carbohydrate hydrolysis, but it does help to inactivate this particular enzyme.

Now here for step b, we're gonna say further hydrolysis in the small intestines produces a mixture of monosaccharides. Now these mixture monosaccharides could be in the form of glucose, fructose, galactose. Right. So these are things to keep in mind when we're starting to talk about carbohydrate metabolism.

Intro To Carbohydrate Metabolism Concept 2

When looking at the stages of food catabolism, remember we're starting out with our starch, glycogen, and disaccharides, or large sugar molecules. We use saSalivary alpha-amylase in step a to help break them down. By the time they reach our stomach, these polysaccharides are smaller in length. Some of them get to the point where they are disaccharides or oligosaccharides. And remember, the stomach itself does not secrete any enzymes. What it does is it inactivates our salivary alpha-amylase, which halts carbohydrate digestion. It's in step b where we have further enzymes taking effect in the small intestines, which will help break down these larger sugar molecules into monosaccharides.

From there, we go into steps stages 2, 3, and 4, where we have acetyl CoA formation, which then goes into the Krebs cycle or the citric acid cycle. Remember in this cycle we have the creation of our electron carriers in the form of NADH, FADH₂. We also have the production of some ATP as well as carbon dioxide. This NADH can then go into the electron transport chain or oxidative phosphorylation that we know of to help to create even more ATP. In addition to this, remember stages 3 and 4 are coined our common metabolic pathway.

Now the enzymes in the small intestines include pancreatic alpha-amylase, maltase, which helps to break down maltose, sucrase, which helps to break down sucrose, and lactase, which helps to break down lactose. Right? So keep in mind these different stages of our food catabolism and the different types of enzymes that we find in the small intestines that help to break down our larger carbohydrates into monosaccharides.

Intro To Carbohydrate Metabolism Example 1

Here it says, which of the following carbohydrates is hydrolyzed by the enzyme in saliva? So we know that we have our starches, and our polysaccharides and our disaccharides initially. And the enzyme that we're using is our salivary alpha amylase. This is our enzyme since it ends with "ase". This enzyme would basically react with our carbohydrate. Carbohydrates end with "ose". So, the sugar would have to be Amylose. The answer here would be option A. The amylose carbohydrate will be affected by the salivary alpha amylase, the enzyme found within our saliva. This helps to break down our food into smaller carbohydrate molecules.

Where does the digestion of milk sugar take place? Which enzyme catalyzes the reaction?

• A. Mouth, α-amylase
• B. Small intestine, lactase
• C. Stomach, α-amylase
• D. Small intestine, α-amylase

Here’s what students ask on this topic:

What is the role of salivary alpha amylase in carbohydrate digestion?

Salivary alpha amylase plays a crucial role in the initial stage of carbohydrate digestion. It is an enzyme found in saliva that hydrolyzes starch and glycogen into smaller polysaccharides and maltose. This process begins in the mouth, where mechanical chewing breaks down food, and salivary alpha amylase starts the biochemical breakdown. The enzyme specifically targets the glycosidic linkages in polysaccharides, converting them into smaller sugar molecules. However, once the food reaches the stomach, the acidic environment inactivates salivary alpha amylase, halting further carbohydrate digestion until the food reaches the small intestine.

How does the stomach contribute to carbohydrate digestion?

The stomach contributes to carbohydrate digestion primarily by creating an acidic environment that inactivates salivary alpha amylase, halting the initial breakdown of carbohydrates. Unlike the mouth and small intestine, the stomach does not secrete enzymes specifically for carbohydrate hydrolysis. Instead, its role is to prepare the food for further digestion by mixing it with gastric juices, which contain hydrochloric acid. This acidic environment denatures proteins and inactivates enzymes like salivary alpha amylase, ensuring that carbohydrate digestion resumes in the small intestine with the help of other enzymes.

What enzymes are involved in carbohydrate digestion in the small intestine?

Several enzymes are involved in carbohydrate digestion in the small intestine. Pancreatic alpha amylase continues the breakdown of polysaccharides into smaller oligosaccharides and disaccharides. Specific disaccharidases then act on these smaller molecules: maltase breaks down maltose into two glucose molecules, sucrase breaks down sucrose into glucose and fructose, and lactase breaks down lactose into glucose and galactose. These enzymes ensure that carbohydrates are fully hydrolyzed into monosaccharides, which can then be absorbed into the bloodstream and utilized for energy production.

What is the citric acid cycle and its role in carbohydrate metabolism?

The citric acid cycle, also known as the Krebs cycle, is a crucial metabolic pathway in carbohydrate metabolism. It occurs in the mitochondria after glycolysis and the formation of Acetyl CoA. The cycle involves a series of chemical reactions that produce electron carriers NADH and FADH₂, as well as ATP and carbon dioxide. These electron carriers then enter the electron transport chain, where they contribute to oxidative phosphorylation, generating a significant amount of ATP. The citric acid cycle is essential for converting the energy stored in carbohydrates into a usable form for cellular processes.

What are the stages of food catabolism in carbohydrate metabolism?

Food catabolism in carbohydrate metabolism involves several stages. Initially, large carbohydrate molecules like starch and glycogen are broken down by salivary alpha amylase in the mouth. In the stomach, this enzyme is inactivated, halting digestion temporarily. In the small intestine, further hydrolysis occurs with the help of enzymes like pancreatic alpha amylase, maltase, sucrase, and lactase, producing monosaccharides. These monosaccharides are then absorbed and enter metabolic pathways, including glycolysis, the citric acid cycle, and oxidative phosphorylation, ultimately generating ATP and electron carriers like NADH and FADH₂ for energy production.