Metabolic Pathways Cheat Sheet

Metabolic pathways are sequences of chemical reactions in organisms, fueled by energy and substrates, essential for life. They involve building complex molecules (anabolic) and breaking down simple ones (catabolic), with energy transfer primarily managed through ATP.

Core Principles

• Metabolism encompasses all chemical reactions within a cell or organism.
• Anabolic pathways build complex molecules, consuming energy.
• Catabolic pathways break down complex molecules, releasing energy.
• Entropy measures disorder; living systems maintain order by using energy.
• Energy is conserved (First Law) and transformed (Second Law of Thermodynamics).
• Exergonic reactions release energy (spontaneous), endergonic reactions require energy.
• Free energy change (ΔG) predicts reaction spontaneity.
• Redox reactions involve electron transfer (oxidation loses electrons, reduction gains).
• ATP is the primary energy currency, powering cellular work.
• Enzymes are biological catalysts that speed up reactions by lowering activation energy.
• Glycolysis breaks down glucose into pyruvate, producing ATP and NADH.
• Cellular respiration (including the citric acid cycle and oxidative phosphorylation) generates significant ATP.
• Allosteric regulation and feedback inhibition control enzyme activity and pathway flux.

Action Steps

• Identify the starting molecule and the final product of the pathway.
• Determine if the pathway is anabolic (building) or catabolic (breaking down).
• Assess the energy requirements (endergonic) or release (exergonic) for each step.
• Trace the flow of electrons in redox reactions.
• Recognize ATP as the energy currency and how it's generated and used.
• Understand the role of enzymes in catalyzing reactions.
• Apply feedback inhibition principles to regulate pathway activity.
• Consider the impact of temperature and pH on enzyme function.

Formulas

• $ΔG = ΔH - TΔS$
• $ΔG < 0$: Exergonic (spontaneous, energy released)
• $ΔG > 0$: Endergonic (non-spontaneous, energy required)
• Oxidation: Lose Electrons (OIL)
• Reduction: Gain Electrons (RIG)
• $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$ (Cellular Respiration Summary)
• $ΔG_{reaction} = ΔG_{products} - ΔG_{reactants}$

Key Terms

• Metabolic Pathway: A series of chemical reactions occurring in a cell or organism, fueled by energy and substrates.
• Anabolic Pathway: Builds complex molecules from simpler ones, consuming energy (e.g., protein synthesis).
• Catabolic Pathway: Breaks down complex molecules into simpler ones, releasing energy (e.g., digestion).
• Entropy (ΔS): A measure of disorder or randomness in a system.
• Free Energy (ΔG): The energy available to do work in a biological system.
• Exergonic Reaction: A reaction that releases free energy, often spontaneous.
• Endergonic Reaction: A reaction that requires an input of free energy, non-spontaneous.
• Oxidation: The loss of electrons from a molecule.
• Reduction: The gain of electrons by a molecule.
• ATP (Adenosine Triphosphate): The primary molecule for storing and transferring energy in cells.
• Enzyme: A biological catalyst, usually a protein, that speeds up chemical reactions.
• Activation Energy (Ea): The minimum energy required to initiate a chemical reaction.
• Glycolysis: The breakdown of glucose into pyruvate, occurring in the cytosol.
• Allosteric Regulation: Regulation of an enzyme's activity by binding a molecule at a site other than the active site.
• Feedback Inhibition: A regulatory mechanism where the end product of a pathway inhibits an enzyme earlier in the pathway.

Timeline

• Early 20th Century: Concept of metabolic pathways and enzyme kinetics developed.
• 1930s-1940s: Elucidation of the Krebs cycle (Citric Acid Cycle) by Hans Krebs.
• 1940s-1950s: Discovery of ATP's role as the energy currency by Fritz Lipmann.
• 1950s: Understanding of oxidative phosphorylation and the electron transport chain.
• 1960s: Detailed mapping of glycolysis and other major metabolic pathways.
• Late 20th Century - Present: Advancements in understanding metabolic regulation, systems biology, and metabolic engineering.

People

• Hans Krebs: Nobel laureate, known for the Citric Acid Cycle (Krebs Cycle).
• Fritz Lipmann: Nobel laureate, identified ATP as the primary energy currency.

Quiz

• Which type of metabolic pathway builds complex molecules and consumes energy?: Anabolic
• What molecule serves as the primary energy currency in cells?: ATP
• Which process involves the loss of electrons?: Oxidation
• Where does glycolysis occur in eukaryotic cells?: Cytosol