Introduction to Metabolism: Catabolism and Anabolism

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Questions and Answers

Briefly explain how feedback inhibition regulates metabolic pathways, providing an example.

Feedback inhibition is a regulatory mechanism where the end product of a metabolic pathway inhibits an enzyme earlier in the pathway, preventing overproduction. For example, in amino acid synthesis, high levels of the amino acid can inhibit the first committed step of its synthesis.

Describe the main differences between catabolism and anabolism, providing an example of each.

Catabolism is the breakdown of complex molecules into simpler ones, releasing energy (exergonic), like the breakdown of glucose into carbon dioxide and water during cellular respiration. Anabolism is the synthesis of complex molecules from simpler ones, requiring energy (endergonic), such as protein synthesis from amino acids.

Explain the importance of shuttle systems in metabolism with a specific example.

Shuttle systems are essential for transporting molecules across the mitochondrial membrane, as it is impermeable to many key metabolites. For example, the malate-aspartate shuttle transports NADH equivalents from the cytosol into the mitochondrial matrix for use in the electron transport chain.

Outline the three main stages of catabolism and what happens during each stage.

<ol> <li>Hydrolysis of large molecules: Breakdown of complex molecules into smaller subunits.</li> <li>Conversion of subunits to a common intermediate: Smaller subunits are converted into acetyl-CoA or other central metabolites.</li> <li>Oxidation of acetyl-CoA: Acetyl-CoA is oxidized in the citric acid cycle, generating ATP and reducing power (NADH and FADH2).</li> </ol> Signup and view all the answers

Describe two ways that metabolic pathways are regulated.

Metabolic pathways are regulated through: 1) allosteric control of enzymes by metabolites and 2) hormonal control of enzyme synthesis or activity. Allosteric control can involve either activation of inhibition via specific molecules. Hormonal control involves signaling molecules affecting gene expression and/or post-translational modification. Signup and view all the answers

Explain the role of membrane transporters in metabolism, giving a specific example.

Membrane transporters facilitate the movement of specific molecules across cellular membranes, enabling metabolic processes to occur in different cellular compartments. For example, the glucose transporter GLUT4 allows glucose uptake into muscle and fat cells in response to insulin. Signup and view all the answers

Explain substrate-level regulation in the context of metabolic pathways and give an example.

Substrate-level regulation of a metabolic pathway involves the direct interaction of a substrate or product with an enzyme to affect its activity. For instance, high concentrations of ATP can inhibit phosphofructokinase-1 (PFK-1) in glycolysis, reducing the rate of glucose breakdown when energy levels are high. Signup and view all the answers

In what ways does the compartmentalization of metabolic pathways contribute to the overall efficiency of cellular metabolism?

Compartmentalization concentrates enzymes and substrates, increasing reaction rates. It also prevents interference between opposing pathways, allowing simultaneous operation. Furthermore, it creates specific microenvironments optimized for particular metabolic processes (e.g., low pH in lysosomes). Signup and view all the answers

Distinguish between short-term and long-term regulation of metabolic pathways.

Short-term regulation involves rapid adjustments like allosteric control and covalent modification of enzymes, responding to immediate changes in cellular conditions. Long-term regulation entails changes in enzyme synthesis rates mediated by hormones or transcription factors, adapting to sustained metabolic needs or environmental cues. Signup and view all the answers

Explain how futile cycles are regulated to prevent energy wastage.

Futile cycles, where two opposing metabolic reactions occur simultaneously without net change, are regulated through reciprocal control mechanisms. For example, if one reaction is activated by a high energy charge (ATP), the opposing reaction is inhibited, preventing the wasteful consumption of energy with no overall metabolic progress. Signup and view all the answers

Flashcards

Metabolism

The sum of all chemical processes occurring in an organism, essential for life, growth, and function.

Catabolism

Breakdown of complex molecules into simpler ones, releasing energy.

Anabolism

Synthesis of complex molecules from simpler ones, requiring energy.

Catabolic Pathways

Degradative pathways breaking down complex molecules.

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Anabolic Pathways

Biosynthetic pathways that build complex molecules.

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Regulation of Metabolic Pathways

Mechanisms controlling the flux of metabolites through metabolic pathways.

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Shuttle systems

Systems that transport molecules across cellular membranes.

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Study Notes

Biochemistry is the study of chemical processes in living organisms.

Overview of Metabolism

Metabolism refers to the complete set of chemical reactions that occur in living organisms to sustain life.
Catabolism is the breakdown of complex molecules into simpler ones, releasing energy in the process.
Stages of catabolism include:
- Hydrolysis of complex molecules into their building blocks.
- Conversion of building blocks into simpler intermediates.
- Oxidation of intermediates to common end products, like CO2, H2O, and NH3.
Anabolism is the synthesis of complex molecules from simpler ones, requiring energy input.

Subdivisions of Metabolism

Metabolism includes catabolism and anabolism.

Catabolism vs. Anabolism

Catabolism:
- Breaks down complex molecules.
- Releases energy (exergonic).
- Includes processes like glycolysis, beta-oxidation, and the citric acid cycle.
Anabolism:
- Synthesizes complex molecules.
- Requires energy (endergonic).
- Includes processes like protein synthesis, gluconeogenesis, and fatty acid synthesis.

Regulation of Metabolic Pathways

Metabolic pathways are regulated to maintain homeostasis and respond to changing energy needs.
Regulation occurs through:
- Enzyme activity modulation (e.g., allosteric regulation, covalent modification).
- Control of enzyme synthesis (e.g., induction or repression of gene expression).
- Compartmentation of metabolic pathways within cells.
- Hormonal regulation (e.g. insulin, glucagon).
- Energy charge of the cell (ATP/ADP ratio).

Shuttle Systems and Membrane Transporters

Shuttle systems and membrane transporters facilitate the movement of molecules across cellular membranes.
Allows metabolites to move between different cellular compartments (e.g., cytosol, mitochondria).
Examples include:
- Glycerol-3-phosphate shuttle.
- Malate-aspartate shuttle.
- Carnitine shuttle.
- ATP-ADP translocase.