ENERGY AND ENZYMES Ch. 6

FLOW OF ENERGY  Energy is the ability to do work or bring a change.  There are 2 types of energy  Kinetic- Energy of motion  Potential- Stored energy

LAWS OF THERMODYNAMICS  There is a constant flow of energy in biological systems.  The laws of thermodynamics explain why energy flows through ecosystems and cells.  First Law of Thermodynamics- Law of conservation of energy (Energy cannot be created or destroyed, but it can change forms)  Second Law of thermodynamics- Energy cannot change forms without a loss of usable energy.

ENTROPY  The second law of thermodynamics can be restated as energy transformation make the universe less organized.  The term Entropy is used to indicate the relative amount of disorganization.

METABOLIC REACTIONS  In cell biology, we use the concept of free energy instead of entropy.  Free energy (ΔG) is the amount of energy left to do work after a chemical reaction has occurred.  ΔG is determined by subtracting the free energy content of the reactants from that of the products.  A –ΔG mean that the products have less free energy than the reactants. This is a endergonic reaction- meaning energy is required.  A +ΔG is an exergonic reaction or spontaneous.

ATP  ATP, or adenosine triphosphate, is the common energy currency of the cell.  ATP is constantly being generated from ADP (adenosine diphosphate) and an inorganic phosphate molecule.  ATP supplies come from the breakdown of glucose and other biomolecules. Only 39% of the free energy in glucose is converted to ATP.

APT STRUCTURE  ATP is a nucleotide of the base adenine and the 5-carbon sugar ribose (together called adenosine) and 3 phosphate groups.  ATP is a “high energy” molecule because the phosphate groups are easy to remove.

The ATP cycle

COUPLED REACTIONS  ATP hydrolysis is coupled to endergonic reactions so these reactions can have enough energy for the reaction to occur.

 Example: Muscle Contractions

ENZYMES  Enzymes are protein molecules that speed up a chemical reaction without being affected itself.  Ribozymes are RNA that also serve as biological catalyst.

METABOLIC PATHWAYS  Metabolic pathways are a series of linked chemical reactions.  There can be many steps in metabolic pathway, in which each step requires a different enzyme to catalyze the reaction.  The product of one reaction becomes the reactant of the next reaction. E 1 E 2 E 3 E 4 E 5 A  B  C  D  E  F

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