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H Human Biology U1KA6
Dec 6, 2024
Lecture Notes: Metabolic Pathways
Introduction to Metabolic Pathways
Metabolism
: Refers to all chemical reactions in a cell, broken into two main types:
Anabolism
: Synthesis of large molecules from smaller substrates (requires energy)
Catabolism
: Breakdown of large molecules into smaller products (releases energy)
Metabolic Pathways
: Integrated series of enzyme-catalyzed reactions within a cell.
Pathways are controlled, involve substrates and products
Example: Respiration is a classic metabolic pathway
Anabolism vs. Catabolism
Anabolism
: Builds up large molecules; requires energy
Example: Protein synthesis from amino acids
Catabolism
: Breaks down large molecules; releases energy
Example: Respiration (glucose + oxygen -> energy + water + carbon dioxide)
Characteristics of Metabolic Pathways
Reversible Steps
: Some reactions can go back and forth
Irreversible Steps
: Locked step (example: initial steps in glycolysis)
Alternative Routes
: When intermediates are either converted further or rerouted
Enzyme Functionality
Enzyme Active Site
: Complementary to substrate, promotes reaction
Induced Fit Model
: Active site changes shape for substrate binding
Enzymes lower activation energy, making reactions more feasible
Factors Affecting Reaction Rates
Substrate Concentration
:
Increased substrate leads to increased reaction rate, until active sites are saturated
At saturation, reaction rate is limited by enzyme concentration
Product Concentration
: Feedback inhibition occurs when end-product accumulates
Example: Inhibition of early enzymes to prevent resource wastage
Types of Enzyme Inhibition
Competitive Inhibition
:
Inhibitor competes with substrate for active site
Can be overcome by increasing substrate concentration
Non-Competitive Inhibition
:
Inhibitor binds to a distinct site, altering enzyme shape
Not overcome by increasing substrate concentration
Summary
Metabolic pathways are essential for cell function and involve controlled, enzyme-mediated reactions
Anabolism builds up, while catabolism breaks down molecules
Enzymes speed up reactions by lowering activation energy through the induced fit model
Reaction rates can be affected by substrate/product concentration and enzyme inhibition mechanisms (competitive and non-competitive)
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