Metabolism:
Energy and Enzymes
Chapter 6
Energy = the ability to do work
Kinetic Energy - energy of motion
Potential Energy - stored energy
First Law of Thermodynamics - the law of conservation of energy
Second Law of Thermodynamics - energy cannot be changed
without a loss of usable energy (heat)
Metabolic Reactions
Reactants  Products
a+b
 c+d
Exergonic: releases energy
Endergonic: absorbs energy
ATP - the energy
currency of cells
(adenosine triphosphate)
Functions:
1. CHEMICAL WORK Supplies energy needed
to make macromolecules
that make up the cell (and
organism)
2. TRANSPORT WORK Supplies energy needed
to pump substances
across the cell membrane
3. MECHANICAL WORK
- supplies energy needed
to make muscles contract
and other cellular parts to
move (flagella)
Metabolic Pathways & Enzymes (6-3)
Enzyme - protein molecule that functions as an organic catalyst to
speed reactions
Substrate - reactants in the enzymatic reaction, this is what an
enzyme attaches to
Energy of Activation - the energy required to cause the reaction
Properties of Enzymes:
• Enzymes are made of
proteins.
• They speed up
•
•
•
chemical reactions
inside the cytoplasm.
They are needed only
in small amounts
They remain
unchanged after each
reaction and can
therefore be reused
Each enzyme is
specific for a substrate
Induced Fit Model - substrates and enzymes fit together
like a lock and key.
(Degradation vs Synthesis)
breaking down vs building
Factors Affecting Enzymatic Speed
1. Substrate concentration
2. Temperature & pH *
3. Enzyme concentration
Enzymes can be denatured - they change shape so much that they are no longer
effective. High temp or pH can cause denaturation.
Siamese cats have an enzyme that works at lower
temperatures only, causing the nose and ears to
become a darker color than the rest of the body.
Enzymatic Inhibition - when
a substance binds to an
enzyme and decreases its
activity. (Usually reversible)
Two types:
Competitive Inhibition
Noncompetitive Inhibition
(allosteric site)
**Both are forms of
feedback inhibition
Some inhibitors are NOT reversible - poisons like
cyanide, lead poisoning all affect enzymes
QUESTION: What type of inhibition is pictured below?
Enzyme Quiz
http://www.sciencegeek.net/Biology/review/U2Enzymes.htm
Enzyme Lab(s)
2H2O2 ----> 2H2O + O2
Hydrogen Peroxide is broken down by the enzyme: catalase within
cells.
KMNO4 (potassium permanganate) can be used to determine how
much H2O2 is left within the flask after the reaction has
stopped. (Titration)
The more KMnO4 you use,
the more peroxide is left
in the flask.
You slowly add
KMnO4, which is
purple, to the flask.
The peroxide in the
flask causes the
KMnO4 to lose color
when the solution is
mixed thoroughly.
When all the
peroxide has reacted
with KMnO4, any
additional KMnO4 will
remain light brown or
pinkish even after
you swirl the
mixture. This is the
endpoint. Record the
amount of KMnO4
you have used.
The activity of
catalase can be
seen by the
bubbling of oxygen
during the reaction
Generally speaking,
catalase reactions occur
faster at warmer
temperatures.
If temperature is too hot
(boiling) then the
enzyme becomes
denatured
Virtual Labs with Enzymes
McGraw Hill Lab
Bio 114 Enzymes
Lab Bench Enzyme Catalysis
Use the following vocabulary in your
discussions
Functional group
Carboxyl group
Amino group
Hydroxyl group
Double bond
Single bond
C-C bonds
Nucleic acid
Protein
Lipid
Carbohydrate
Amino Acid
Nitrogen base
Carbon rings
Phosphate group
Enzyme
Substrate
Monosaccharide
Disaccharide
Fatty Acids
Steroids