Energy Flow in the Life of a Cell
Chapter 5
What is Energy?
Capacity to do
work
Forms of energy
Kinetic energy
Potential energy
Chemical
Gravitational
What Is Energy?
From
potential energy to kinetic energy
What Can Cells Do
with Energy?
Energy inputs
become coupled to energy-requiring processes
Cells use energy
for:
Chemical work
Mechanical work
Electrochemical work
First Law of Thermodynamics
The total amount
of energy in the universe remains constant
Energy can
undergo conversions from one form to another, but it cannot be created or
destroyed
Second Law of Thermodynamics
No energy
conversion is ever 100 percent efficient
The total amount
of energy is flowing from high-energy forms to forms lower in energy
Entropy
Matter tends to
become disorganized
Entropy is the
measure of the degree of disorder in a system
The world of life
can resist the flow toward maximum entropy only because it is resupplied with energy from the sun
One-Way Flow of Energy
The sun is lifes
primary energy source
Producers trap
energy from the sun and convert it into chemical bond energy
All organisms
use the energy stored in the bonds of organic compounds to do work
What Is Energy?
To recap:
Energy Cannot Be
Created or Destroyed
Energy Tends to
Become Distributed Evenly
Matter Tends to
Become Less Organized
Living Things Use
the Energy of Sunlight
to Create Low-Entropy Conditions
Energy Changes &
Cellular Work
Energy
changes in cells tend to
run spontaneously in the direction that results in a decrease in usable energy
and in organization.
Cells
counter this with energy gained from the outside.
Exergonic Reactions
Energy is
released
Products have
less energy than starting substance
Endergonic Reactions
Energy input
required
Product has more
energy than starting substances
Endergonic or Exergonic?
Endergonic or Exergonic?
All Reactions Require an Initial Input of
Energy
Energy Relationships
The Role of ATP
Cells earn ATP
in exergonic reactions
Cells spend ATP
in endergonic reactions
Electron Carriers
Energy from
excited electrons can be captured for use in endergonic
reactions
Common carriers
of excited electrons:
NAD
FAD
How Do Cells Control Their Metabolic
Reactions?
At Body
Temperatures, Many Spontaneous Reactions Proceed Too Slowly to Sustain Life
Catalysts Reduce
Activation Energy
Enzymes are the
major biological catalysts
Activation Energy
For a reaction to
occur, an energy barrier must be surmounted
Enzymes make the
energy barrier smaller
Participants in
Metabolic Pathways
Energy Carriers
Enzymes
Cofactors
Types of Reaction Sequences
How Do Cells Control Their Metabolic Reactions?
Enzymes are
biological catalysts
The structure of
enzymes allows them to catalyze specific reactions
They speed the
rate at which reactions approach equilibrium
Four Features of Enzymes
1)
Enzymes do not make anything happen that could not happen on its own. They just
make it happen much faster
2)
Reactions do not alter or use up enzyme molecules
Four Features of Enzymes
Induced-Fit
Model
Substrate
molecules are brought together
Substrates are
oriented in ways that favor reaction
Active sites may
promote acid-base reactions
Active sites may
shut out water
Factors Influencing
Enzyme Activity
Temperature
pH
Salt
concentration
Allosteric
regulators
Coenzymes
and cofactors
Effect of Temperature
Small increase in
temperature increases molecular collisions, reaction rates
High temperatures
disrupt bonds and destroy the shape of active site
Effect of pH
Allosteric Activation
Allosteric Inhibition
Feedback Inhibition
Enzyme Helpers
Cofactors
Coenzymes
NAD+, NADP+,
FAD
Accept electrons
and hydrogen ions; transfer them within cell
Derived from
vitamins
Metal ions
Ferrous iron in cytochromes
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