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

Intro to Metabolism Concept 1

Everyone. So in this video, we're going to talk about Metabolism. Now when we say Metabolism, well, that refers to all biochemical reactions that take place within an organism. And when we're referring to metabolism, we're talking about catabolism versus anabolism. With catabolism, we're going to say we have reactions that produce energy by breaking down molecules into smaller ones. And the opposite of catabolism is anabolism. With anabolism, we say that these are reactions that use energy to build larger molecules from smaller ones.

If we take a look here at this image, we're going to say we have our larger molecules here. And if we're going this way, we're breaking them down into smaller molecules. Remember, smaller molecules mean that we're going to do catabolism. And as we break it down, we're releasing energy over here. If we look the opposite way, we're taking some energy, we're investing it into our smaller molecules in order to build up to larger molecules. Going this way is anabolism. So just remember, catabolism, we're breaking down to produce energy. Anabolism, we're building up, but it requires energy to do so.

Intro to Metabolism Examples 1

In this example question, we need to identify each of the following processes as anabolism with an "a," or catabolism with a "c." For the first one, we're going to say trypsin in the small intestine converts proteins into smaller peptides. Since proteins, which are larger, are being broken down into something smaller, this process is Catabolism. Therefore, this would be labeled as "c." Next, glucose is converted to glycogen for storage. Remember, glucose is a monosaccharide and glycogen is a polysaccharide, which is essentially many glucose molecules strung together. Thus, we're going from a smaller molecule in the form of glucose to a larger molecule in the form of glycogen. This building up into something bigger indicates Anabolism. Lipase in the stomach hydrolyzes lipids to fatty acids and glycerol. "Hydrolyzes" means using water to break bonds, breaking things down into smaller pieces. This process is Catabolism. Lastly, amino acids in ribosomes are converted into proteins. Here, amino acids are connected to each other through bonds, going from our primary structure all the way to our quaternary structure to make our proteins. We're going from a smaller molecule to a much larger molecule. So, this is Anabolism. This is how we identify each one of these statements whether it's Anabolism with an "a" or Catabolism with a "c."

Metabolic Pathways Concept 2

Now, we know that Metabolism consists of Anabolism and Catabolism. Well, both of them take place through Metabolic Pathways. And we're going to say recall, a metabolic pathway is a sequence of interconnected biochemical reactions taking place in an organism. These metabolic pathways can be either linear so if we take a look here, we're starting out with our molecule a. It undergoes some type of reaction with enzyme 1 to create b, and then it continues with another enzyme to create c, and then c lastly goes to d with the help of a third enzyme. But they can also be cyclic. So in this one, we have a here, but then it goes cyclic like this. Within this chapter, we're going to take a look at both linear as well as cyclic pathways in relation to metabolism.

Metabolic Pathways Example 2

Of the following statements about metabolic pathways is correct? So for A, it says the product of the last reaction in a cyclic metabolic pathway is a reactant in the first reaction. This is true. Remember, when we looked at the cyclic pathway, we ended with our product D. But product D can feed back into our first reactant A and the cycle begins all over again. So, basically the product of a reaction can help to become, the substrate or reactant of the next reaction. So here, A is true.

Catabolism always takes place through cyclic pathways. That is not true. Catabolism could go through linear or cyclic pathways. We talked about both possibilities when it comes to metabolism.

Linear catabolic pathways produce energy while cyclic catabolic pathways use energy. We never said this. All we said is that there are two types of pathways. There are linear as well as cyclic. We never talked about either of them creating energy or using energy.

And then here, the last reaction in some linear pathways can produce a starting material for the first reaction. Now in a linear reaction, think of it as a chain of reactions connected together, interconnected together, and it's an assembly line. At the end of the assembly line, that's it. That's our last product. That product doesn't loop back around to make our beginning reactant. So here, option A would be the only correct statement.

Stages of Catabolism Concept 3

Now, when it comes to the stages of catabolism, we're going to say that energy production through catabolism of food takes place in 4 stages. So, we have stages 1 to 4 here. We're going to say connected to this idea is aerobic respiration. We're going to say the predominant energy production pathway in the body takes place in the presence of oxygen gas, so O2 gas. If we take a look here, we have stage 1. We're starting out with our proteins, carbohydrates, and lipids. These are present outside of the cell. Stage 1 deals with digestion. We're consuming these things and digestion is going to help us break them down. The proteins are broken down into their amino acids, carbohydrates into their monosaccharides, and our lipids into their fatty acids. Once we pass this barrier, which means that we're going into the cells, we have aerobic respiration taking place.

In Stage 2, we're going to say we have Acetyl CoA formation. So here we have Acetyl CoA, represented by this structure. In stage 3, it can go into the citric acid cycle. We're going to have the production of our electron carrying structures in the form of NADH, FADH2. We also have the creation of ATP or energy and Carbon Dioxide. Finally, from stage 3 to stage 4, we have our electron transport chain and oxidative phosphorylation, which leads to even more production of energy in the form of ATP.

Here, we're going to say that stages 3-4 are called our common metabolic pathway. We're going to say that means that stages 3-4 are identical for the catabolism of all food types. Because at this point, it's broken down to such a fundamental level that everything is going to be the same in terms of stages 3-4. Stages 1-2 are not the same throughout because different enzymes are required to break down proteins, carbohydrates, and lipids into their respective amino acids, monosaccharides, and fatty acids. We can also say that for stage 2, different pathways are needed for amino acids, monosaccharides, and fatty acids. So there's a lot of differences in stages 1-2. But stages 3-4 is where we have our common metabolic pathway.

Right? So this just gives us a great overview, broad overview of the stages of food catabolism, where we're breaking down foods that we consume.

Stages of Catabolism Example 3

Which of the following statements about the catabolism of food is incorrect?

• A. Carbohydrates are oxidized in stage 1 to produce carbon dioxide and energy. This statement is incorrect because remember in stage 1, we have the digestion of carbohydrates to create our respective monosaccharides. So this is incorrect. So this is our answer.
• B. Acetyl CoA is the product of stage 2 Catabolism. That is true, we make Acetyl CoA which then goes into the citric acid cycle to produce energy as well as carbon dioxide.
• The electron transport chain in oxidative phosphorylation is the last stage of food catabolism. That is true. That eventually leads to the production of more ATP energy.
• The Citric acid cycle uses Acetyl CoA to produce energy. Yes. The Acetyl CoA that goes into the Citric Acid Cycle does produce energy as well as CO₂. This statement is true.

So out of all our options, only option A is incorrect.

Which one of the following catabolism stages produces NADH?

• A. Electron transport chain
• B. Glycogenolysis
• C. Digestion
• D. Citric acid cycle