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Catabolism and Anabolism – Metabolism and Regulation

by Kevin Ahern, PhD
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    00:01 In order to be alive, cells must generate energy and use that energy to make molecules.

    00:07 That's the function of what we call metabolism. In this presentation I will go through the processes of catabolism and anabolism, I'll deal with energy considerations as they regard biochemical reactions and finally talk about regulation and mechanisms.

    00:22 First I need to define some terms. Catabolism is a process whereby larger molecules that the cell takes in, are broken down into smaller components. You can see on the screen for example that proteins, polysaccharides and fats are broken respectively into amino acids, sugars and fatty acids. These precursors or these building blocks that were used to make the larger molecules are in turn broken down into smaller components and though there are a variety of these components that are made, a common one that they all converge to is acetyl-CoA. Acetyl-CoA can be oxidized readily in the citric acid cycle to generate ATP energy.

    01:01 The process of oxidation of course generates electrons and those electrons in the cell must be dealt with. The electrons in cells are placed on electron carriers, either NAD+ or FAD typically, NAD+ is shown here. When NAD+ accepts electrons and a proton, it becomes NADH as you can see on the presentation.

    01:22 The process of anabolism is essentially the opposite of catabolism, that is, smaller molecules are built into precursors and those precursors are made into the building blocks of the individual larger components. So we can see here for example that the precursors are made into amino acids, sugars and fatty acids to make respectively, proteins, polysaccharides and fats. Because this process requires energy, ATP input is necessary and the ATP generated by the catabolic processes is used to make the molecules here in the anabolic processes.

    01:57 Anabolism usually is reductive, meaning that it requires electrons and so electron sources are needed to make these larger molecules. Electron sources come from a variety of things, but typically NADH can be used.

    02:13 Now as I noted in the previous presentation, cells are governed by the rules of the universe.

    02:17 They can't violate the ways that energy is used and stored, so they have to work within those constraints. Now consider for example what cells must do in oxidizing glucose.

    02:30 This metabolic pathway is known as glycolysis and in glycolysis, the very first reaction involves the addition of a phosphate to glucose. If the cell were to try to simply put a phosphate on to glucose, it would encounter the reaction shown at the very top, where glucose is added to a phosphate, creating a molecule known as glucose-6-phosphate. Now delta G 0 prime (ΔG0') for that reaction is +15 kJ per mol. It's possible to make that reaction go, but that very positive ΔG0' value makes it somewhat of a barrier and makes it difficult for the cell to make glucose-6-phosphate. So rather than try to push that reaction excessively, cells have another alternative that they can use to make the reaction favorable. The consideration that the cells have, is that they have an energy source and the energy source that they have is ATP. Now ATP as you see in the second line, can be hydrolyzed using water, to create ADP plus phosphate. Now the ΔG0' for that reaction is very negative, -31 kJ per mol.

    03:37 So what cells do to overcome the barrier of the first reaction is to couplet with the second reaction. When these two reactions are put together, then what happens is the reaction overall becomes energetically favorable. In this case glucose, plus ATP, is used to generate glucose-6-phosphate plus ADP, and for this reaction the ΔG0' is -16 kJ per mol, that is the sum of the two previous reactions. So by pairing an energy releasing reaction, with an energy requiring reaction, also called coupling, cells can overcome energy barriers.


    About the Lecture

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


    Included Quiz Questions

    1. The larger molecules are broken to smaller ones
    2. Energy is required
    3. The process is usually non-oxidative
    4. Polysaccharides are made
    1. It makes energetically unfavorable processes more favorable
    2. It is usually the mechanism of making ATP
    3. It is necessary to make catabolic processes occur
    4. It occurs when NAD+ is produced

    Author of lecture Catabolism and Anabolism – Metabolism and Regulation

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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