Metabolic Pathways – Metabolism and Regulation

by Kevin Ahern, PhD

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    00:01 As we think about metabolism and in fact as we discuss metabolism, people will refer to metabolic pathways. Now pathways are rather like roadmaps or a highway, we can think of a highway as connecting several towns and each town is a stop along the way. One town follows another town, follows another town, and the same thing happens with metabolic pathways.

    00:21 In this case, we can see the metabolic pathway of glycolysis. Glucose is converted into glucose-6-phosphate, which is in turn converted into fructose-6-phosphate etc. There are ten reactions overall in the glycolysis pathway. Now it's very important to remember that though we talk about the pathway as an entity unto its own and isolated from everything else, it's very important to remember that it's not that case, that is these reactions that are occurring, are occurring in the literal soup of the cell and in this soup of the cell, there are thousands of interrelated reactions that are going on at the same time. So in this figure for example I've shown on the left, the different metabolic pathways that also involve some of the molecules of glycolysis. So for example glucose is used in and produced in the metabolism of glycogen.

    01:13 Glucose-6-phosphate is used in gluconeogenesis, in the Calvin cycle, the pentose phosphate pathway etc. So none of these molecules works in isolation. It is instructive and it is organizationally important for us to think about these pathways as being separate, but to also remember that they don't occur in isolation inside of cells. Here's the last half of glycolysis and you can see that every intermediate in glycolysis, intersects with at least one other pathway and in some cases three or four.

    01:45 Now this diagram shows, not molecules connecting with each other, but in fact pathways connecting with each other, so that you can have a better idea how the intermediates of one pathway intersect another pathway. So for example, the pathway here that starts out and says sugars is the glycolysis pathway that I just referred to, and we can see that the sugars pathway leads to intermediates that are produced in the citric acid cycle. The citric acid cycle in turn can go to a variety of things including, let's say amino acids, as shown on the left. So you'll also notice that these arrows that are drawn between the pathways go both ways. So that means for example that cells can take amino acids that they get from breaking down proteins and use those in the citric acid cycle to generate energy, to generate fatty acids, or even to make sugars depending upon the cell.

    About the Lecture

    The lecture Metabolic Pathways – Metabolism and Regulation by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. They are multi-step processes, each requiring a specific enzyme.
    2. They occur in isolation inside of cells.
    3. They always have a catabolic component.
    4. They do not share molecules with each other.
    5. They are normally spontaneous reactions.

    Author of lecture Metabolic Pathways – Metabolism and Regulation

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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