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An Introduction to Metabolism - Coggle Diagram
An Introduction to Metabolism
An Organism's Metabolism
Definition of Metabolism
Metabolism: The totality of an organism's chemical reaction.
Emergent Property: Arises from interactions between molecules within the cell.
Purpose: Manages the material and energy resources of the cell.
Metabolic Pathways
Definition: Series of chemical reactions that build or break down molecules.
Types:
-Catabolic Pathways:
break down complex molecules to simple molecules.
EX: Cellular respiration breaks down glucose to CO2 and H2O.
Energy released used to do cellular work.
-Anabolic Pathways:
Build complex molecules from simple molecules.
EX: Synthesis of proteins from amino acids.
Energy consumed required energy input (endergonic).
Energy and Its Form
Energy: Capacity to cause change, can be used to do work, move matter against opposing forces, such as gravity and friction.
Forms of Energy:
Kinetic Energy: is energy associated with motion ( heat = random movement of molecules).
Ex: water gushing through a dam turns turbines.
Thermal Energy: is the kinetic energy associated with random movement of atoms or molecules.
Potential Energy: is energy that matter possesses
because of its location or structure.
Ex: water behind a dam possesses energy because of its altitude above sea level.
Chemical Energy: is potential energy available for release in a chemical reaction.
Ex: Glucose has high chemical energy due to its structure.
The Law of Thermodynamics
First Law ( Conservation of Energy):
Energy can be transferred or transformed, but not created or destroyed.
Ex: Cells transform chemical energy in food to kinetic energy (movement).
Second Law ( Entropy):
Every energy transfer increases the entropy (disorder) of the universe.
Implication: Some energy becomes unusable (as heat).
Spontaneous Process: Occurs without energy input; increases entropy.
Entropy and Biological Order
Organisms maintain order by using energy to counteract entropy.
Ex: Building complex molecules (low entropy) requires energy from food or sunlight.
The Free Energy Charge of a Reaction
Free Energy (G)
Definition: is the portion of a system’s energy that can do work when temperature and pressure are uniform throughout the system, as in a living cell.
Formula: ΔG = ΔH – TΔS
ΔG = change in free energy
ΔH = change in enthalpy (total energy)
ΔS = change in entropy
T = Temperature in Kelvin (K)
Spontaneous and Nonspontaneous Reactions
Spontaneous Reaction: ΔG < 0 (negative); releases free energy (exergonic).
Example: Cellular respiration.
Nonspontaneous Reaction: ΔG > 0 (positive); requires energy input (endergonic).
Example: Photosynthesis.
Exergonic vs. Endergonic Reactions
Exergonic: Energy released; spontaneous.
Ex: ATP hydrolysis.
Endergonic: Energy absorbed; nonspontaneous.
Ex: synthesis of macromolecules.
Free Energy in Metabolism
Coupled Reactions: Energy released from exergonic reactions drives endergonic ones.
Ex: ATP hydrolysis powers active transport or biosynthesis.
Equilibrium and Work
At Equilibrium: ΔG = 0; system cannot do work.
Cells Avoid Equilibrium: Constant flow of materials keeps metabolic pathways working.
Systems Stability vs. Unstable Systems
Free energy can be thought of as a measure of a
systems stability; unstable systems (higher G) tend
to become more stable (lower G).
For example, a diver on a platform is less stable than
when floating in the water.
A drop of concentrated dye is less stable than when
it is dispersed randomly through a liquid.
A glucose molecule is less stable than the simpler
molecules into which it can be split
ATP Power Cellular Work
Structure and Function of ATP
ATP (Adenosine Triphosphate):
Composed of adenine (nitrogen base), ribose (sugar), and three phosphate groups.
Function: Primary energy currency of the cell.
Energy from ATP Hydrolysis
Reaction: ATP + H2O --> ADP + Pi + energy
Repulsion between negatively charged phosphate groups.
ΔG = –7.3 kcal/mol (under standard conditions).
How ATP Drives Work
Energy Coupling: Using exergonic ATP hydrolysis to drive endergonic processes.
Chemical work—pushing endergonic reactions.
Transport work—pumping substances across membranes against the direction of spontaneous movement.
Mechanical work—such as beating cilia or contracting muscle cells.
Phosphorylated Intermediate: Recipient molecule gains a phosphate group --> more reactive.
Regeneration of ATP
ATP Cycle:
ADP + Pi --> ATP (endergonic, requires energy from catabolism).
ATP --> ADP + Pi (exergonic, powers cellular work).
Continuous Cycle: Each ATP molecule recycled thousands of times per day.
Enzymes Speed Up Metabolic Reactions
Catalysts and Activation Energy
Catalyst: Substance that speeds up reaction without being consumed.
Enzyme: Biological catalyst (usually a protein).
Activation Energy (EA): Initial energy needed to start a reaction.
Enzymes lower EA barrier but don’t change ΔG (free energy).
Substrate and Enzyme Specificity
Substrate: Reactant an enzyme acts on.
Active Site: Region where substrate binds.
Induced Fit: Enzyme changes shape slightly to better fit substrate.
Mechanisms of Enzyme Action
Mechanisms to Lower EA:
Orienting substrates correctly.
Straining substrate bonds.
Providing favorable microenvironment.
Forming temporary covalent bonds.
Enzyme Activity Affected By:
Temperature: Each enzyme has optimal range.
pH: Most human enzymes optimal around pH 6–8.
Cofactors: Nonprotein helpers (metal ions or organic molecules).
Coenzymes: Organic cofactors (ex: NAD+, vitamins).
Enzyme Inhibitors
Competitive Inhibitors: closely resemble the substrate, and can bind to the enzyme’s active site.
Noncompetitive Inhibitors: bind to another part of the enzyme, away from the active site.
Examples:
Toxins and poisons often act as inhibitors.
Antibiotics inhibit bacterial enzymes.
Regulation of Enzyme Activity Helps Control Metabolism
Importance of Regulation
Reason: Cells must tightly control metabolism to conserve energy and resources.
Coordinate anabolic and catabolic pathways efficiently.
Allosteric Regulation
Definition:occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site.
Allosteric Activator: Stabilizes active form of enzyme.
Allosteric Inhibitor: Stabilizes inactive form.
Ex: Regulation of enzymes in cellular respiration (ex: phosphofructokinase).
Cooperativity
Definition: substrate binding to one active site triggers a shape change in the enzyme that stabilizes the active form for all other sites
Occurs in: Multisubunit enzymes.
Example: Hemoglobin binding oxygen.
Feedback Inhibition
Definition: End product of a metabolic pathway shuts down the pathway.
Purpose: Prevents overproduction and waste.
Ex: Isoleucine inhibits threonine deaminase (amino acid synthesis pathway).
Compartmentalization of Enzymes
Definition: Enzymes are localized within organelles.
Purpose: Organization and control of metabolic pathways.
Ex: Enzymes for cellular respiration in mitochondria.