Download Chapter 2 Notes – The Chemistry of Life

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Date: _______________________
Chapter 2 Notes – The Chemistry of Life
Section 2-4 Chemical Reactions and Enzymes
Chemical Reactions
Everything that happens in an organism—its ________________, its interaction
with the __________________________, its ______________________, and even its
movement—is based on chemical reactions.
A chemical reaction is a process that ___________________ one set of chemicals
into another set of _____________________.
•
Some chemical reactions occur _______________
o Combustion of ____________ and __________________  iron oxide
(a.k.a. rust)
•
Other reactions occur ___________________
o ___________________ gas (H2) ignited in the presence of
_________________ (O2)  rapid and explosive reaction
Reactants = the elements or compounds that ____________ into a chemical
reaction.
Products = the element or compounds ____________________ by a chemical
reaction.
What happens to chemical bonds during chemical reactions?
Chemical reactions always involve the ___________________ of bonds in
reactants and the ______________________ of new bonds in products.
Example of an important chemical reaction in your body:
•
______________ _________________ (CO2) is constantly being produced by
normal ________________ activity.
•
CO2
lungs (exhaled)
Bloodstream
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CO2 is not ________________ in H2O; the two react in the following
•
chemical reaction: 
+
H2CO3 (how CO2 is carried)
•
(carbonic acid)
Bloodstream
lungs (exhaled)
When you exhale, the reaction is reversed:

(carbonic acid)
+
Energy in Reactions
Energy is ______________________ or _____________________ whenever
chemical bonds form or are broken.
Because chemical reactions involving breaking and forming bonds, they
•
involve changes in __________________.
How do energy changes affect whether a chemical reaction will occur?
Chemical reactions that release energy often occur
___________________________. Chemical reactions that absorb energy will not
occur without a __________________ of energy.
Example: When hydrogen gas (H2) reacts with oxygen to produce water vapor, it
is an ______________________________________ reaction, in which energy is
given off as ___________________.
2H2 + O2 !
2H2O
Reversing this reaction would require the addition of large amounts of
___________________.
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What is the significance of energy changes in living things?
In order to stay alive, organisms need to carry out ___________________ that
require energy.
•
Because _________________ and __________________ are conserved in
chemical reactions, every organism must have a source of energy to carry
out _________________ reactions.
o Plants get their energy from the ____________.
o Animals get their energy from eating _____________ and other
________________.
o Humans release energy by ___________________ food (so we can
breathe, grow, think, dream, etc.)
Activation Energy
Chemical reactions that _________________ energy do not always occur
spontaneously.
•
Activation energy = the energy needed to get a reaction _________________.
o It is a factor in whether the overall chemical reaction releases
energy or absorbs energy.
o In other words, the amount of activation energy needed determines
how easily __________________ can form _________________.
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Enzymes
Some chemical reactions that make life possible are too ___________ or have
activation energies that are too ___________ to make them practical for living
tissue.
•
These chemical reactions are made possible by ____________________.
o Catalyst = a substance that ________________ up the rate of a
chemical reaction.

Catalysts work by __________________ a reaction’s
activation energy.
Lowering the activation
energy has a dramatic effect
on how quickly the reaction
is completed (reactants
converted to products)
Why are enzymes important to living things?
•
Enzymes are __________________ that act as biological catalysts.
•
Enzymes speed up chemical reactions that take place in ______________.
•
Enzymes act by lowering the ______________________ energy.
Back to the carbon dioxide example…
CO2 + H2O  H2CO3
•
Left to itself, this reaction is so slow that CO2 would build up in the body
_____________ than the bloodstream could _______________ it.
•
Your bloodstream has an enzyme (carbonic anhydrase) that speeds up this
reaction by a factor of ________ million.
o Reaction takes place immediately; CO2 is removed from the blood.
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Enzymes are very ___________________, generally catalyzing only one chemical
reaction.
•
For this reason, part of an enzyme’s name is usually derived from the
reaction it ____________________.
Enzyme Action
For a chemical reaction to take place, the reactants must ______________ with
enough energy so that existing bonds will be _________________ and new bonds
will be _________________.
•
If reactants do not have enough ______________, no reaction will take
place.
The Enzyme-Substrate Complex
Enzymes provide a site where reactants can be brought together to
______________, reducing the energy needed for reaction.
•
Substrates = the _____ _____________ of enzyme-catalyzed reactions.
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•
The substrates ___________________ and ___________ bind to the
________________ ___________ on the enzyme, hexokinase, forming an
enzyme-substrate complex.
o The fit is so precise that the active site and substrates are often
compared to a ___________ and _________.
•
The enzyme and substrates remain bound together until the reaction is
done and the substrates are converted to __________________.
•
The products of the reaction (glucose-6-phosphate and ADP) are
__________________ and the enzyme is free to start the process again.
Regulation of Enzyme Activity
Enzyme can be affected by any _________________ that influences a chemical
reaction.
•
Enzymes work best at certain __________ values.
o In the human body, most enzymes work best around pH ________.
•
Many enzymes are affected by changes in _________________________.
o In the human body, most enzymes work best at temperatures close
to ___________°C
Cells can _____________________ the activities of enzymes.
•
Most cells contain ___________________ that help to turn key enzymes
“on” and “off” at critical stages in the life of the cell.
Enzymes play essential roles in:
•
regulating chemical _____________________.
•
making _____________________ that cells need.
•
releasing ________________.
•
transferring _________________________.
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