BISC 130 - Chapter 6: Metabolism

Energy

• The ability to do work

• There are 2 types

  1. Potential energy (stored energy)

     1. Includes chemical energy

        1. Energy in chemical bonds. Breaking these releases energy

1. Kinetic Energy

   1. Energy of motion

   2. Includes heat

• First law of Thermodynamics:

  • Energy cannot be created or destroyed

  • Only converted from one form to another

Chemical Reactions

• 2 types:

  1. Exergonic Reaction

     1. Products are at lower energy than the reactants (starting materials, beginning)

     2. Exergonic releases energy

1. Endergonic Reaction

   1. Products are at higher energy than the reactants

   2. Requires input of energy

• These 2 reactions can be joined/coupled together.

• Both reactions need to overcome an activation energy (an additional energy input) to proceed - a hump.

  • This prevents reactions from occuring spontaneously

• Heat Energy can be used to overcome activation energy

  • Not feasible/doesn't work in cells

• Activation energy can be lowered by catalysts

Catalysts

• Holds reactant(s) and strain the chemical bonds in order to lower activation energy

• Can facilitate exergonic or endergonic reactions.

• Biological Catalysts (most are proteins) are called enzymes.

Enzyme Catalysis

1. Substrate(s) bind at the enzyme's active site.

   • They form the enzyme/substrate complex

   • Enzymes are very specific for their substrate(s)

1. Enzyme changes shape slightly to better fit substrate(s)

   1. This is called Induced Fit

1. Strains chemical bonds in the substrate(s), lowering activation energy

   1. For exergonic reactions, ambient heat energy is now enough to overcome activation energy.

2. Chemical reaction occurs

1. Product(s) released

2. The enzyme assumes its original shape

   1. Not altered by the reaction - free to work again.

• Enzyme Inhibitors reduce an enzyme's function

• Enzyme activators increase an enzyme's function

• Some Enzymes require cofactors and/or coenzymes in order to function