Biology 101 Chapter 5

The Working Cell


Metabolism: The ability of living systems to acquire and use energy for growth and repair.


Energy: The capacity to do work.



1) Kinetic Energy = energy actually performing work.

Ex. heat, light, momentum

2) Potential Energy = stored energy.

Ex. gravity, chemical


Two Laws Govern Energy Reactions

       Life depends on energy; it can be changed from one form to another


1) The First Law of Thermodynamics (Law of Conservation)


2) The Second Law of Thermodynamics (Law of Entropy)


Entropy: the measure of the amount of disorder in a system.

Chemical reactions either store or release energy.

Reactions may be:

Endergonic (endothermic)

Exergonic (exothermic)


Activation Energy: The energy needed to kick-start a chemical reaction. All reactions have activation energy.


Enzymes: Are organic catalysts that speed up chemical reactions.


Properties of Enzymes: The Basic Rules

1.   Enzymes only speed up reactions, they cannot make a reaction occur if it would not occur on own.


2.   Enzymes are not consumed, used up, destroyed, altered, or harmed in anyway by the reaction. They are recycled.


3.   Enzymes are very selective about their substrate. One to one rule.


4.   Enzymes will work both the forward and reverse reactions of a particular type of reaction.


       Enzymes are organic, they are made of proteins.

       They speed up reactions by lowering the activation energy.

       Enzymes are embedded in the cell's membranes.

       They perform many of the body's functions.


Factors That Affect the Enzyme

1.   Temperature

2.   pH

3.   Salt concentration

4.   Pressure

5.   Substrate concentration

6.   Enzyme concentration

7.   Electronegativity

8.   Inherent enzyme function


Enzyme Control and Inhibition

Role of negative feedback

Positive feedback


Competitive Inhibitors

Non-competitive Inhibitors



Substrate = that which an enzyme acts upon


Active Site = the working point or region of an enzyme


Reactants = starting materials


Products = ending materials





Intermediates = compounds in between start and finish


reactants intermediates products


Metabolic Reaction vs. Metabolic Pathway











Chloroplasts and Mitochondria

       Make energy available for work

       Photosynthesis and Cellular Respiration are circular processes


Photosynthesis: 6 CO2 + 6 H2O → 1 C6H12O6 + 6 O2


Respiration: 1 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O


ATP and Its Role in Energy Reactions

       Energy currency of cell

       Recycled process

       Redox reactions

o     Something reduced = gained electrons

o     Something oxidized = lost electrons

       Oxidation-Reduction reactions always coupled