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Chapter 8 – An Introduction to Metabolism - Coggle Diagram
Chapter 8 – An Introduction to Metabolism
Metabolism: An Overview
Metabolism = totality of an organism’s chemical reactions
Manages material and energy resources
Metabolic Pathways
Specific molecule → product via enzyme-catalyzed steps
Catabolic pathways: break down molecules (e.g., cellular respiration)
Anabolic pathways: build molecules (e.g., protein synthesis)
Forms of Energy
Energy = capacity to cause change or do work
Kinetic Energy – motion (e.g., thermal energy)
Potential Energy – stored energy due to structure/location
Chemical Energy – potential energy in chemical bonds
Thermodynamics
First Law: Energy cannot be created or destroyed
Second Law: Every energy transfer increases entropy (disorder)
Free Energy (G) and Spontaneity
Free Energy (G) = energy that can do work
ΔG = change in free energy
ΔG < 0 → spontaneous (exergonic)
ΔG > 0 → nonspontaneous (endergonic)
Equilibrium = no net change in ΔG, system at max stability
Exergonic Reaction
Releases energy
ΔG negative
e.g., cellular respiration
Endergonic Reaction
Consumes energy
ΔG positive
e.g., photosynthesis
ATP – The Energy Currency
Adenosine Triphosphate (ATP)
3 phosphate groups + ribose + adenine
Hydrolysis of ATP
Releases energy by breaking phosphate bond
ΔG ≈ –7.3 kcal/mol
Phosphorylation
ATP transfers phosphate to another molecule
Drives endergonic reactions
Enzymes and Catalysis
Enzyme = catalytic protein
Speeds up reactions by lowering activation energy
Does not change ΔG
Substrate and Active Site
Substrate = reactant enzyme acts on
Active site = region where substrate binds
Induced Fit = enzyme changes shape slightly to fit substrate
Catalytic Cycle
Substrate enters active site
Substrate enters active site
Substrate converted to product
Product released; enzyme unchanged
Factors Affecting Enzyme Activity
Temperature
Too high → denaturation
Each enzyme has an optimal range
pH
Affects shape/charge of active site
Most enzymes optimal around pH 6–8 (exceptions: pepsin, pH ~2)
Cofactors & Coenzymes
Cofactors = nonprotein helpers (metal ions)
Coenzymes = organic cofactors (e.g., vitamins)
Enzyme Inhibition
Competitive Inhibitors
Bind active site
Compete with substrate
Noncompetitive Inhibitors
Bind elsewhere
Change enzyme shape → less effective active site
Allosteric Regulation & Feedback Inhibition
Allosteric Regulation
Regulatory molecule binds enzyme at one site, affects function at another
Can activate or inhibit
Often involves enzymes with multiple subunits
Cooperativity
Binding of one substrate increases affinity of other subunits
Example: hemoglobin
Feedback Inhibition
End product of pathway inhibits early enzyme
Prevents waste of resources