The document discusses how life requires energy derived primarily from sunlight via photosynthesis. It then explains that life can be viewed as coordinated chemical reactions, and that enzymes play a key role in allowing these reactions to occur by lowering their activation energy. Specifically, enzymes allow organisms to couple favorable, energy-releasing reactions to unfavorable, energy-requiring reactions through the use of ATP as an energy currency.

1. Energy and Enzymes
Life requires energy.
Almost all energy for life is derived from the
sun.
A “factoid” -
The sun’s energy that strikes Earth each day
is equivalent to one million Hiroshima-sized
atomic bombs.
Photosynthesis harnesses about 1% of that
energy – 10,000 “atomic bomb equivalents”
per day.

2. Chemistry and Life
One unromantic yet productive way of
viewing life is to see it as a set of
coordinated chemical reactions.
This leads to an obvious question – What
determines what chemical reactions are
possible?

3. Chemical Reactions
Whether a chemical reaction will or won’t occur under particular
conditions is determined by the laws of thermodynamics.
Keeping it simple -
If the overall amount of order is decreased by a reaction, the
reaction is favored.
If the overall amount of order is increased by a reaction, the
reaction is not favored.

4. The Direction of Spontaneous Reactions
(and what it takes to go the other way)
Going this way is possible, but it requires the input of energy.

5. Life Requires Lots of Unfavorable Reactions – How Is This Possible?
favorable unfavorable
reactions reactions
By coupling
favorable, energy-
releasing reactions to
unfavorable, energy-
requiring reactions.

6. The “Nature of Life” – Coupling Favorable, Energy-Yielding
Reactions to Unfavorable, Energy-Requiring Reactions

7. Even When Cells Build Complex Molecules and Structures, the Second
Law of Thermodynamics (Entropy or the “kids bedroom principle”)
Isn’t Violated

8. ATP - Life’s
Energy
Currency
Energy is released
when ATP is
hydrolyzed (broken
down) to ADP.
ATP is restored
from ADP and an
input of energy.
ATP’s energy is
used to drive
endergonic
(energy-requiring)
reactions.

9. The Way ATP Often
Works

10. Enzymes Speed Biochemical Reactions
Enzymes are biological catalysts – substances that speed a reaction
without being altered in the reaction.
Most enzymes are proteins, some are RNA.
Enzymes are essential for life.
Model of the surface of an enzyme.

11. Enzymes
Lower a
Reaction’s
Activation
Energy

12. Enzyme Action

13. The Fit Between Enzyme and Substrate is Critical and Precise
Hexokinase
, an enzyme
(blue),
binding its
substrate,
glucose
(yellow).

14. Many
Enzymes
Work by
Altering the
Shape of
Their
Substrates
The active site
of an enzyme is
where substrate
is bound.

15. Metabolic Pathways
The synthesis of biological molecules often requires many enzyme-
catalyzed steps.
The entire set of steps is a metabolic pathway.

16. Enzyme Activity is Often
Regulated
Feedback inhibition - a
common form of enzyme
regulation in which the
product inhibits the enzyme .