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Chapter 6
Energy Flow in the Life of a Cell
Chapter 6 Outline
• 6.1 What Is Energy?
• 6.2 How Does Energy Flow in Chemical
Reactions?
• 6.3 How Is Cellular Energy Carried Between
Coupled Reactions?
• 6.4 How Do Cells Control Their Metabolic
Reactions?
6.1 What Is Energy?
• Energy is the ____________________
• Work is a force acting on an object that
causes the object to _________
• _________________ is the energy that
powers life
– The objects that move are __________,
which reposition during chemical reactions
The Laws of Thermodynamics
• The two fundamental types of energy
– Kinetic energy is the energy of __________
• e.g. light, heat, electricity, moving objects
– Potential energy is _____________ energy
• e.g. chemical energy in bonds, electrical
charge in a battery, a rock at the top of a
hill
The Laws of Thermodynamics
• The laws of thermodynamics describe
the availability and usefulness of energy
– ________________________________
(first law of thermodynamics)
– The total amount of energy within a given
system remains __________ unless energy
is added or removed from the system
The Laws of Thermodynamics
• Availability and usefulness of energy:
– The amount of useful energy __________
when energy is converted from one form to
another (second law of thermodynamics)
– Entropy (disorder) ______________
Energy of Sunlight
• Living Things Use the Energy of Sunlight to
Create the _____________ Conditions
Characteristic of Life
• __________________ organisms use
external solar energy to maintain orderly
structure
• ____________________ organisms use
stored chemical energy in other living things
to counter increasing entropy
Section 6.2 Outline
• 6.2 How Does Energy Flow in Chemical
Reactions?
– The Nature of Chemical Reactions
– Exergonic Reactions ___________ Energy
– Endergonic Reactions ___________ an Input
of Energy
– Coupled Reactions _______Exergonic and
Endergonic Reactions
Chemical Reactions
•
•
Chemical reactions are processes that
____________________________
between atoms
Chemical reactions convert _________
to products
Reactants
Products
Chemical Reactions
•
Reactions can be categorized as
exergonic or endergonic based on
energy gain or loss
Exergonic Reactions
•
•
Exergonic reactions __________ energy
Reactants contain _______ energy than
products in exergonic reactions
Exergonic Reactions
•
Exergonic reaction example: the burning
of glucose
Exergonic Reactions
•
All chemical reactions require an initial
energy input (____________________) to
get started
– Molecules need to be moving with sufficient
collision speed
– The electrons of an atom repel other atoms
and inhibit bond formation
Endergonic Reactions
• Endergonic reactions are _______________
___________________________ of energy
• Products contain _______ energy than
reactants in endergonic reactions
Endergonic Reactions
• Endergonic reaction example:
photosynthesis
Coupled Reactions
• ______________ reactions drive
_____________ reactions
– The product of an energy-yielding reaction
fuels an energy-requiring reaction in a
_________________
Coupled Reactions
• The exergonic and endergonic parts of
coupled reactions often occur at different
places within the cell
• ___________________________ are
used to transfer the energy within cells
Section 6.3 Outline
• 6.3 How Is Cellular Energy Carried
Between Coupled Reactions?
– Energy Carrier Molecules
– ______ Is the Principal Energy Carrier in
Cells
– ____________________ Also Transport
Energy Within Cells
Energy Carrier Molecules
• Food energy cannot be used _______ to
power energy-requiring reactions (e.g.
muscle contraction)
• Energy carrier molecules act as
______________ to carry energy between
__________ and _____________ reactions
• Energy carrier molecules are only used
within cells because they are ________
ATP
• ______________________ (ATP) is the
most common energy carrying molecule
• ATP is composed of an adenosine
molecule and ______ phosphates
ATP
• Energy is stored in the high-energy bond
extending to the _________________
• Heat is given off when ATP breaks into
_____ (adenosine diphosphate) and ___
(phosphate)
ATP
• The energy released when ATP is broken
down into ADP + P is transferred to
______________ reactions through
coupling
Electron Carriers
•
•
•
Energy can be transferred to
__________ in glucose metabolism and
photosynthesis
Electron _________ transport highenergy electrons
Two common electron carriers
1. Nicotinamide adenine dinucleotide ______
2. Flavin adenine dinucleotide _______
Section 6.4 Outline
• 6.4 How Do Cells Control Their
Metabolic Reactions?
– Overview of Metabolism
– At Body Temperatures, Spontaneous Reactions
Proceed Too ________to Sustain Life
– Catalysts __________ Activation Energy
– Enzymes Are Biological ______________
– Cells Regulate Metabolism by __________
Enzymes
– Poisons, Drugs, and Environmental Conditions
Influence ___________________
Overview of Metabolism
•
•
The sum of all the chemical reactions
inside a cell is its __________________
Many cellular reactions are linked
through metabolic _______________
Overview of Metabolism
•
Metabolic pathways proceed smoothly
for three reasons:
1. Endergonic reactions are _______ with
exergonic reactions
2. Energy-carrier molecules capture
energy and ____________ between
endergonic and exergonic reactions
3. Chemical reactions are regulated
through protein _______________
Spontaneous Reactions
•
•
At body temperatures, spontaneous
reactions proceed too _________ to
sustain life
Reaction speed is generally determined
by the activation energy required
– Reactions with low activation energies
proceed _________ at body temperature
– Reactions with high activation energies (e.g.
sugar breakdown) move very _______ at
body temperature, even if exergonic overall
Spontaneous Reactions
•
•
Enzyme molecules are employed to
___________(speed up) chemical
reactions in cells
Catalysts ________________ of a
chemical reaction without themselves
being used up
Catalysts Reduce Activation Energy
• Catalytic converters in cars facilitate the
conversion of carbon monoxide to carbon
dioxide
Octane + oxygen
carbon dioxide + water + energy + carbon
monoxide
(poisonous)
• Catalyst in catalytic converter speeds carbon
monoxide conversion
Carbon monoxide + oxygen
carbon dioxide + energy
Catalysts Reduce Activation Energy
• Catalysts speed up spontaneous reactions
by ____________________________
Enzymes Are Biological Catalysts
•
•
Enzymes __________________________
molecules in the process of lowering activation
energy
Enzymes (proteins) differ from non-biological
catalysts because:
1. Enzymes are very ___________ for the molecules
they catalyze
2. Enzyme activity is often ____________________ by
their reactants or products
•
Some enzymes require helper ___________
molecules to function (e.g. certain B vitamins)
Enzyme Structure
•
•
Enzymes have a pocket called an _________
Reactants (_________) bind to the active site
– Distinctive shape of active site is complementary
and specific to the substrate
– Active site amino acids bind to the substrate and
distort bonds to facilitate a reaction
Enzyme Structure
•
Three steps of enzyme
catalysis
1. Substrates enter the
_________ in a specific
orientation
2. Upon binding, the
substrates and enzyme
_____________ to
promote a reaction
3. Products of the reaction
________ the active site,
leaving the enzyme ready
for another catalysis
Cells Regulate Metabolism
•
•
A given enzyme usually catalyzes a single
step in a chain of metabolic reactions
Metabolic pathways are controlled in
several ways
1. Control of _____________________
regulates availability
2. Some enzymes are inactive when
synthesized and must be _____________
__________________
Cells Regulate Metabolism
•
Metabolic pathways are
controlled in several
ways (continued)
3. Small organic
molecules can bind to
enzymes and
___________________
activity (allosteric
regulation)
Cells Regulate Metabolism
•
Metabolic pathways are controlled in
several ways (continued)
4. Adequate amounts of formed product inhibit
enzyme activity ___________________
Drugs and Poisons
•
•
•
Drugs and poisons often inhibit
enzymes by ____________
with the natural substrate for
the active site
This process is known as
_______________________
Some inhibitors bind
permanently to the enzyme
Environmental Conditions
•
•
Three-dimensional structure of an enzyme
is sensitive to ______________________
______________________________
Most enzymes function optimally only within
a very narrow range of these conditions
Environmental Conditions
•
•
Enzyme structure is
_________ and
function is destroyed
when pH is _________
_____________
Salts in an enzyme’s
environment can also
destroy function by
altering ___________
Environmental Conditions
•
Temperature also
affects enzyme
activity
– Low temperatures
______________
molecular movement
– High temperatures
cause ___________
to be altered,
destroying function