Overview of Metabolism

Overview of Metabolism

• Metabolism is the entire set of enzyme-catalyzed transformations of organic molecules in living cells
• Living cells and organisms carry out work to stay alive, grow and reproduce
• Organisms carry out energy transformations
• Organisms use chemical energy from fuels (food) for synthesis of complex macromolecules from simple precursors
• Organisms use chemical energy for concentration gradients, motion, and heat

Anabolism and Catabolism

• Anabolism: The phase of intermediary metabolism where the synthesis of cell components from smaller precursors occurs (typically a reductive process)
• Catabolism: The phase of intermediary metabolism where nutrient molecules are degraded to yield energy (typically an oxidative process)

Energy Manipulations in Cells

• Metabolic pathways are series of reactions where molecules are degraded or synthesized
• Some pathways release energy; others require energy
• ATP is the energy currency of life, it can be given to pathways that need energy or produced by pathways that release energy
• ATP can be formed by the oxidation of carbon compounds like glucose and fatty acids
• Metabolic pathways are regulated by regulatory enzymes

Structure and Function of ATP

• ATP is the energy currency of cells
• ATP links catabolism and anabolism
• ATP consists of adenosine (adenine + ribose) and three phosphate groups
• Phosphate groups have negative charges which repel each other, making the molecule unstable, and when hydrolyzed release energy.

ATP Cycle

• ATP cycle carries energy from catabolism to energy-requiring processes in cells
• When we eat, nutrients (food) are oxidized by catabolic pathways to produce ATP
• ATP is needed for muscle contraction
• ATP is converted to ADP + P_i
• ADP + P_i can be converted back to ATP using energy from the catabolism of nutrients

Energy-Rich Compounds

• ATP is not the only energy rich compound that can be spontaneously hydrolyzed and release energy
• Amount of energy released by ATP is small, so it can be resynthesized when another energy-rich compound is hydrolyzed (that releases more energy). Examples of some phosphorylated compounds, include; Phosphoenolpyruvate, 1,3-bisphosphoglycerate, Creatine phosphate, Glucose 1-phosphate, and glucose 6-phosphate
• PEP, 1,3-BPG and creatine phosphate release more energy than ATP hydrolysis

How ATP is Synthesized

• Substrate-level phosphorylation: A metabolic reaction that results in ATP production, supported by the energy released from another high-energy bond, leading to the phosphorylation of ADP
  • This process is quicker and less efficient than oxidative phosphorylation
  • It can occur in the absence of mitochondria or anaerobiosis
• Oxidative phosphorylation: A process, catalyzed by ATP synthase in mitochondria, where free phosphate is bonded to ADP using energy from the electron transport chain
  • It's the most frequent source of ATP production
  • Oxygen is required

Catabolism Overview

• Catabolism is a process where substrates (lipids, carbohydrates, proteins) lose electrons in an oxidative process.
• Oxidized coenzymes (NAD+, FAD⁺) collect the electrons from substrates
• Electrons are transferred to the electron transport chain to allow for ATP formation

Oxidation-Reduction (Redox) Reactions and Coenzymes

• A redox reaction is one where electrons are transferred from a donor to an acceptor molecule
• Oxidation: The loss of electrons from a compound
• Reduction: The gain of electrons by a compound
• Examples of redox coenzymes include NAD⁺/NADH, NADP⁺/NADPH and FAD⁺/FADH₂

Dive into the world of metabolism, exploring the key processes of anabolism and catabolism. Understand how living cells transform energy and synthesize complex molecules from simpler precursors. This quiz covers essential metabolic pathways and the role of ATP as the energy currency of life.