Chemical reactions occur when atoms have enough energy to combine, or change, bonding partners.

sucrose + H2O glucose + fructose

(C12H22O11) (C6H12O6) (C6H12O6)

reactants products

Metabolism—the sum total of all chemical reactions occurring in a biological system at a given time

Metabolic reactions involve energy changes.

CHEMICAL REACTIONS AND METABOLISM HOMEWORK!Study the slides for tomorrow’s quiz. If you have any questions, write them down and hand to me the first 3 minutes of class tomorrow!

All forms of energy can be considered as either:

Potential—the energy of state or position, or stored energy

Kinetic—the energy of movement (the type of energy that does work) that makes things change

Energy can be converted from one form to another.

Two basic types of metabolism:

Anabolic reactions link simple molecules to form complex ones.

• They require energy inputs; energy is captured in the chemical bonds that form.

Catabolic reactions break down complex molecules into simpler ones.

• Energy stored in the chemical bonds is released.

Figure 2.14 Energy Changes in Reactions (Part 1)

Figure 2.14 Energy Changes in Reactions (Part 2)

Concept 2.5 Biochemical Changes Involve Energy

The laws of thermodynamics apply to all matter and energy transformations in the universe.

First law: Energy is neither created nor destroyed.

Second law: Disorder (entropy) tends to increase.

When energy is converted from one form to another, some of that energy becomes unavailable for doing work.

Concept 2.5 Biochemical Changes Involve Energy

If a chemical reaction increases entropy, its products are more disordered or random than its reactants.

If there are fewer products than reactants, the disorder is reduced; this requires energy to achieve.

As a result of energy transformations, disorder tends to increase.

• Some energy is always lost to random thermal motion (entropy).

Concept 2.5 Biochemical Changes Involve Energy

Metabolism creates more disorder (more energy is lost to entropy) than the amount of order that is stored.

Example:

• The anabolic reactions needed to construct 1 kg of animal body require the catabolism of about 10 kg of food.

Life requires a constant input of energy to maintain order.