Cellular Energy and Metabolism: Thermodynamics, ATP, and Enzyme Regulation

Guida di studio - Note intelligenti

Appunti personalizzati basati sui tuoi materiali, ampliati con definizioni chiave, esempi e contesto.

The laws of thermodynamics govern energy transformations in biological systems, influencing how organisms obtain and use energy.

First Law (Law of Energy Conservation): Energy cannot be created or destroyed, only transformed from one form to another.
Second Law: Every energy transfer increases the entropy (disorder) of the universe; some energy is lost as heat in every transformation.
Example: When glucose is metabolized, chemical energy is converted to ATP and heat.

The change in free energy () determines whether a chemical reaction can occur spontaneously.

Spontaneous Reaction: Occurs when is negative; energy is released.
Non-Spontaneous Reaction: Occurs when is positive; energy input is required.
Equation:
Exergonic vs. Endergonic: Exergonic reactions release energy (); Endergonic reactions require energy ().
Example: Cellular respiration is exergonic; photosynthesis is endergonic.

ATP (adenosine triphosphate) is the primary energy currency in cells, coupling exergonic and endergonic reactions.

ATP Structure: Composed of adenine, ribose, and three phosphate groups.
ATP Hydrolysis: Releases energy by converting ATP to ADP and inorganic phosphate ().
Coupling: Energy from ATP hydrolysis drives endergonic reactions.
Main Kinds of Cellular Work: Mechanical (movement), transport (pumping substances), and chemical (building molecules).
Example: Muscle contraction uses ATP for mechanical work.

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy barriers.

Activation Energy (): The energy required to start a reaction; enzymes lower .
Enzyme Specificity: Determined by the shape of the active site; only specific substrates fit.
Induced Fit Model: Enzyme changes shape slightly to fit substrate more closely.
Factors Affecting Enzyme Activity: Temperature, pH, cofactors, and inhibitors.
Example: Pepsin works best at low pH in the stomach.

Cells regulate metabolism by controlling enzyme activity, often through feedback mechanisms.

Allosteric Regulation: Enzyme activity is modulated by molecules binding at sites other than the active site.
Feedback Inhibition: End product of a pathway inhibits an earlier enzyme, preventing overproduction.
Example: Isoleucine biosynthesis is regulated by isoleucine inhibiting the first enzyme in its pathway.

Type of Reaction	Value	Energy Flow	Example
Exergonic	Negative	Releases energy	Cellular respiration
Endergonic	Positive	Requires energy input	Photosynthesis

Factor	Effect on Enzyme	Example
Temperature	Increases rate up to optimum; denatures at high temps	Pepsin optimal at 37°C
pH	Each enzyme has optimal pH	Amylase optimal at pH 7
Cofactors	Required for activity	Mg2+ for DNA polymerase
Inhibitors	Decrease activity	Penicillin inhibits bacterial enzymes

Additional info: Academic context and examples have been added to clarify and expand upon the brief questions in the original file.