04 Energy and Metabolism

Chemical Reactions

Processes where molecules interact, breaking or forming bonds, and absorbing or releasing energy. Billions occur in cells every second.

Combination Reaction

A type of chemical reaction represented as A+B→AB.

Decomposition Reaction

A type of chemical reaction represented as AB→A+B.

Recombination Reaction

A type of chemical reaction represented as AB+CD→AD+CB.

Example of Recombination

CO2 + H2O ↔ H2CO3 (Carbon dioxide + Water ↔ Carbonic Acid) in blood.

Reactants

Starting molecules in a chemical reaction (left side of the arrow).

Products

Molecules formed in a chemical reaction (right side of the arrow).

Reversible Reactions

Reactions that can proceed in both forward and reverse directions, indicated by a double arrow (↔).

Balanced Equations

Chemical equations must have the same number of atoms of each element on both sides. Coefficients indicate the number of molecules, subscripts indicate atoms within a molecule.

Enzymes

Biological catalysts, usually proteins (sometimes RNA), that speed up chemical reactions in living organisms without being consumed.

Catalyst

A substance that speeds up a reaction without being used up.

Substrate

The reactant molecule(s) that an enzyme acts upon.

Active Site

The specific region on an enzyme where the substrate binds and the chemical reaction takes place.

Energy of Activation (E_A)

The initial energy input required for a chemical reaction to occur. Enzymes work by lowering the E_A.

Enzyme Specificity

Enzymes are highly specific; only certain substrates fit into their active site.

Optimal Conditions

Enzymes function best under specific conditions of temperature and pH. Human body enzymes optimal temp is 37 °C; stomach enzymes optimal pH is around 2.

Kinetic Energy

Energy of motion, doing work.

Potential Energy

Stored energy, potential to do work.

Energy Conversion

Energy can change forms (e.g., food energy to energy for life), but cannot be created or destroyed.

ATP (Adenosine Triphosphate)

The cell's main energy currency ('energy battery'). A nucleic acid with adenine base, ribose sugar, and three phosphate groups.

ATP Energy Release

Energy is released when the bond between the 2nd and 3rd phosphate is broken, forming ADP (Adenosine Diphosphate) and inorganic phosphate (Pi). Equation: ATP+H2O→ADP+Pi+Energy.

ADP (Adenosine Diphosphate)

ATP molecule with one phosphate removed; lower energy state ('uncharged battery').

ATP-ADP Cycle

The continuous process of breaking down ATP to release energy for cellular work and regenerating ATP from ADP and P_i using energy from food or sunlight.