The energy from oxidizing food molecules is temporarily stored for later use in energetically unfavorable reactions like synthesis of cellular molecules.
This energy is stored in activated carriers, small organic molecules with one or more energy-rich covalent bonds.
Activated carriers diffuse quickly, transferring energy from energy generation sites to biosynthetic sites in the cell.
Main activated carriers include ATP, NADH, and NADPH, serving as 'currency' in cellular reactions.
Formation of Activated Carriers
Coupling energetically favorable reactions with energetically unfavorable ones captures free energy in a useful form.
Enzyme-catalyzed reactions like glucose oxidation release free energy which is harnessed to form activated carriers.
Energy capture differs from wasteful heat release by converting energy into usable forms for metabolic reactions.
Catalysts and Enzymatic Reactions
Enzymes facilitate and speed up reactions without affecting equilibrium points, holding significant roles in metabolic pathways.
Each pathway reacts to cellular conditions such as energy state (well-fed vs. starving) and environmental stress.
Enzyme Kinetics
Reaction speed is determined by measuring Vmax (maximal velocity) in various substrate concentrations, elucidated through spectrophotometry.
Initial velocity (v) is plotted against substrate concentration ([S]), leading to a classic Michaelis-Menten curve to determine kinetic parameters.
Double-Reciprocal Plot
A different plotting method (1/v vs. 1/[S]) helps extract precise Vmax and KM values, aiding in enzyme performance understanding.
Enzyme Regulation
Products, substrate analogs, and inhibitors can influence enzyme activity, vital for cellular control of metabolic processes.
Inhibitors can be competitive (i.e., competing with substrates) or non-competitive, affecting enzyme performance.
Computer Modeling and Enzyme Behavior
With kinetic data, computational tools can predict how enzymes will operate under various conditions.
Knowledge about reactions can facilitate the redesign of enzymes for commercial or medical purposes.
ATP: The Primary Activated Carrier
ATP is the most pivotal activated carrier in biology, analogous to using potential energy in mechanical systems to perform work.
An ATP cycle maintains the energy source, and ATP hydrolysis powers many reactions.
Phosphorylation Reactions
Energetically unfavorable reactions can be driven through the energy transfer from ATP hydrolysis, providing substrates a high-energy form.
NAD(H) and NADPH: Electron Carriers
These carriers transport high-energy electrons in oxidation-reduction reactions, integral for biosynthesis and cellular metabolism.
NADPH supports anabolic reactions (biosynthesis) while NADH participates in catabolic reactions (energy generation).
Role Differences Between NADPH and NADH
Structurally similar but functionally distinct due to the phosphate group on NADPH, allowing compartmentalization of duties.
Regulating different electron-transfer reactions helps cells balance metabolism effectively.
Other Activated Carriers
Other carriers like FADH2, Acetyl CoA transport various groups (e.g., methyl, acetyl) essential in metabolic processes.
Synthesis of Biological Polymers
Building polymers from monomers requires energy from activated carriers, done through enzyme-mediated condensation reactions.
Glycolysis
A series of glycolytic reactions produces ATP and NADH, exemplifying substrate-level phosphorylation within catabolic pathways.
Controlled through various enzyme mechanisms that dictate energy investment and return, resulting in efficient glycolytic flow.
Fermentation in Anaerobic Conditions
In low oxygen environments, fermentation processes regenerate NAD+ from NADH, crucial for continuous glycolysis.
Pyruvate is converted to fermentation products, maintaining the energy yielding process without direct ATP generation.
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