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

Metabolism encompasses all chemical reactions within an organism, organized into metabolic pathways that transform substrates through a series of steps, ultimately yielding a final product. These pathways are categorized into catabolic pathways, which release energy by breaking down larger molecules, and anabolic pathways, which require energy to synthesize larger molecules from smaller ones. Catabolism is associated with exergonic processes, while anabolism involves endergonic processes. Understanding these pathways is crucial for grasping how organisms manage energy and build cellular structures.

Introduction to Metabolism

In this video, we're going to begin our introduction to metabolism. Metabolism is a term that refers to all of an organism's chemical reactions. When we talk about all of the chemical reactions inside of an organism, that is what metabolism refers to. Now, metabolic pathways are defined as a series of chemical reactions that alter a substrate multiple times before the final product is released. Notice in the example image below, we're showing an image of an example metabolic pathway. Metabolic pathways have multiple steps. Notice that the very first substrate here, substrate A, is being converted into product B by enzyme number 1, but product B is not the final product. Instead, B is going to be converted into C by enzyme 2, and C is further going to be converted into D by enzyme 3, and then, last but not least, D is going to be converted into E by enzyme 4. Here, it is molecule E that acts as the final product of this pathway, and all these other molecules act as substrates to enzymes. Enzymes can work together in a series of steps to convert one substrate into another until the final product is released. When enzymes work together in this fashion, we refer to it specifically as a metabolic pathway. There are two main types of metabolic pathways that you should be aware of, and we'll introduce those two in our next video. So, I'll see you all there.

Catabolic & Anabolic Pathways

In this video, we're going to distinguish between Catabolic and Anabolic Pathways. And so really there are 2 main types of metabolic pathways. The first type is going to be catabolic pathways or catabolism, and the second type is going to be anabolic pathways or anabolism. And so, catabolic pathways or catabolism are going to be pathways that release energy into the environment by breaking down molecules into smaller ones. And anabolic pathways are pretty much the exact opposite. Instead of releasing energy into the environment, they are going to spend energy or require an energy input, and they use that energy in order to build up larger molecules such as DNA and proteins, for instance. And so, catabolic pathways, because they release energy into the environment, they are going to be associated with exergonic processes. And anabolic pathways, because they spend energy or require an energy input, they're going to be associated with endergonic processes. Let's take a look at our image down below to further distinguish between catabolic and anabolic reactions and pathways. Notice over here on the left-hand side we're focusing on catabolism, and over here on the right-hand side we're focusing on Anabolism. Now, Catabolism is all about breaking down molecules, large molecules, into smaller pieces, its smaller components. Whereas anabolism is all about building up, building larger molecules using smaller molecules. And so when you think about catabolism, you can see the word cat that is embedded inside of catabolism, and so when you see catabolism, you could think about a cat, and that's because cats, really all they can do is pounce on a pyramid like this one and break it down into its smaller components. But a cat can't really do the opposite. A cat cannot build this pyramid like what we see here. If you ever see a cat build a pyramid like this, please give me a call. I'd like to see that. But when you think about catabolism, you can think about cats and you can think about cats pouncing on pyramids and breaking down the pyramids like what we see here. Now, anabolism doesn't have the word cat in it, and so if there's no cat to break it down, then it's going to allow for building up. And so notice that over here we've got, for catabolism, the cat is breaking down the molecules into its smaller components, and here we have an enzyme breaking down a larger molecule into its smaller components. And then over here on the right for anabolism, we're showing building up. Notice that the building blocks are being built up into the larger more structured pyramid. And here we're taking the smaller building blocks and the enzyme is converting it into a larger piece here, building up. And so really this is the main difference between catabolism and anabolism. Catabolism is going to break down and anabolism is going to build up. And so that concludes our introduction to catabolic and anabolic pathways, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Which of the following terms specifically describes the metabolic process of breaking down large molecules?

a) Catabolism. 

b) Metabolism.

c) Anabolism.

d) Dehydration.

• A. Catabolism.
• B. Metabolism.
• C. Anabolism.
• D. Dehydration.

Which of the following statements is TRUE regarding anabolic pathways?

a) They are used for digesting sugars.

b) They consume energy to build up polymers from monomers.

c) They release energy by breaking down polymers into monomers.

d) They increase the entropy of the organism.

• A. They are used for digesting sugars.
• B. They consume energy to build up polymers from monomers.
• C. They release energy by breaking down polymers into monomers.
• D. They increase the entropy of the organism.

Here’s what students ask on this topic:

What is metabolism and why is it important?

Metabolism refers to all the chemical reactions that occur within an organism to maintain life. These reactions are organized into metabolic pathways, which transform substrates through a series of steps to yield a final product. Metabolism is crucial because it enables organisms to grow, reproduce, maintain their structures, and respond to environmental changes. It encompasses both catabolic pathways, which break down molecules to release energy, and anabolic pathways, which build larger molecules from smaller ones, requiring energy input. Understanding metabolism is essential for grasping how organisms manage energy and build cellular structures.

What are catabolic and anabolic pathways?

Catabolic and anabolic pathways are the two main types of metabolic pathways. Catabolic pathways, or catabolism, involve breaking down larger molecules into smaller ones, releasing energy in the process. These pathways are associated with exergonic reactions. Anabolic pathways, or anabolism, are the opposite; they require energy to build larger molecules from smaller ones, and are associated with endergonic reactions. For example, catabolism includes the breakdown of glucose during cellular respiration, while anabolism includes the synthesis of proteins from amino acids.

How do enzymes function in metabolic pathways?

Enzymes are biological catalysts that speed up chemical reactions in metabolic pathways. They work by lowering the activation energy required for a reaction to occur. In a metabolic pathway, each step is facilitated by a specific enzyme that converts a substrate into a product. For example, in a pathway converting substrate A to final product E, enzyme 1 converts A to B, enzyme 2 converts B to C, and so on. This sequential action ensures that metabolic processes are efficient and regulated, allowing the organism to maintain homeostasis.

What is the difference between exergonic and endergonic reactions?

Exergonic and endergonic reactions are types of chemical reactions that differ in energy transfer. Exergonic reactions release energy into the environment and are typically associated with catabolic pathways. These reactions have a negative ΔG (Gibbs free energy change), indicating that they occur spontaneously. Endergonic reactions, on the other hand, require an input of energy from the environment and are associated with anabolic pathways. These reactions have a positive ΔG, meaning they are non-spontaneous and need energy to proceed. Understanding these reactions is crucial for studying how cells manage energy.

Why are metabolic pathways regulated?

Metabolic pathways are regulated to ensure that the cell's metabolic needs are met efficiently and to maintain homeostasis. Regulation occurs through various mechanisms, including feedback inhibition, where the end product of a pathway inhibits an earlier step, and allosteric regulation, where molecules bind to enzymes at sites other than the active site to modulate activity. This regulation allows cells to respond to changes in their environment, conserve energy, and allocate resources effectively. Proper regulation is essential for the survival and function of the organism.