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Biochemical Reactions
SBI4U1
Acids
•
•
•
•
produces H+ ions in H2O
pH below 7
Sour taste, conducts electricity
Increase [H+] or [H3O+] ions when
dissolved in water
HCl (aq) + H2O (l)  H3O+ (aq) + Cl- (aq)
Bases
• produces OH- ions in H2O (or accepts/
reacts with H+ ions)
• pH above 7
• Bitter taste, conducts electricity
• Increase [OH-] when dissolved in water
NaOH (s)  Na+ (aq) + OH- (aq)
Strong/Weak Acids and Bases
• Depends on the degree to which they
dissolve into ions
• Strong acids/bases completely ionize in
water (e.g. NaOH, HCl)
100%
HCl (aq) + H2O (l)  H3O+ (aq) + Cl- (aq)
100%
NaOH (s)  Na+ (aq) + OH- (aq)
100%
ionization
• Weak acids/bases only partially ionize in
water
1.3%
CH3COOH (aq) + H2O (l)
H3O+ (aq) + Cl - (aq)
10%
NH3 (aq) + H2O(l)
NH4 + (aq)
+ OH - (aq)
Note: double arrow  represents that reaction is reversible
Acid-Base Buffers
• Cells are sensitive to pH levels
– Cell processes w/ proteins and enzymes (pH
7)
– Blood (pH 7.4, 0.4 increase can be fatal)
Acidosis: blood pH < 7.35
Alkalosis: blood pH >7.45
Blood pH can be affected by food
– Acidic fruits, wine, salad dressing
– Alkaline shrimp, tonic water
Buffers
• Chemical systems with substances that
donate/remove H+ ions when pH changes
Example: Carbonic acid-bicarbonate buffer
H2O + CO2
H2CO3
HCO3- + H+
H2O + CO2
H2CO3
HCO3- + H+
• If too acidic H + will react with HCO3- to
produce H2CO3
– Excess H+ are removed from the solution to
avoid decrease in pH
• If too basic, H2CO3 will ionize to replace H+
– H+ ions are added to avoid increase in pH
Animation:
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swf
Oxidation-Reduction Reactions
Oxidation: loss of electrons (loses hydrogen or
gains oxygen)
Reduction: gain of electrons
Redox Rxn: LEO the lion says GER
LEO loss of electrons is oxidation
GER gain of electrons is reduction
Examples:
C 3H 8 +
LEO
C6H12O6
LEO
5O2
GER

+ 6O2 
GER
3CO2
6CO2
+
H 2O
+ 6H2O
Sugars are oxidized to produce carbon dioxide
and water in cellular respiration.
Condensation/Hydrolysis Rxns
Condensation Rxn: formation of a covalent
bond with the production of water
• Anabolic rxn (makes larger molecules)
Hydrolysis Rxn: formation of a covalent bond
with the addition of water
• Catabolic (breaks down into smaller
molecules)
Animation:
http://www.uic.edu/classes/bios/bios100/lectures/polymer.htm
An H from one
molecule
combines with
an OH from
another. Water
is released and
the two
molecules join.
Water is
added. One H
goes to one
molecule and
the OH to the
other to break
them apart.
Carbohydrates
Note: condensation rxn is also known as dehydration synthesis
Lipids
Protein
Nucleotide
Purine: A and G
Pyrimidine: C, T, U
Enzymes
Activation Energy (EA): energy required for
a rxn to take place
Catalyst: speeds up the rate of a chemical
rxn without being consumed
Enzymes: protein catalysts that increase the
rate of reaction by lowering the EA
• Enzymes typically end in “ase”
• Example:
amylose
amylase
+
H 2O

maltose
• There are many enzymes involved in
digestion: peptase, lipase, maltase
How Enzymes Work:
• Enzymes are made up of long chains of
amino acids
• Enzymes attach to substrates in order to
work
• Most enzymes have globular shapes with
active sites
– Where the substrate binds
Enzyme-Substrate Complex: enzyme with
a substrate that is bound to enzyme’s
active site
In this rxn, a dissacharide sucrose is
broken down into glucose and fructose.
• Since enzymes are protein, they can
become denatured if the temperature or
pH change
• Some enzymes require assistance from
cofactors of coenzymes
– Coenzymes are organic molecules
– Cofactors are metal ions like iron or zinc
Some substances can inhibit enzyme
function:
Competitive Inhibitors: similar to substrate,
bind to active site and block normal
substrate
Non-Competitive Inhibitors: do not
compete with substrate, attach to different
site, change the shape so substrate
cannot bind
Enzyme activity is controlled by:
1. Restricting the production of an enzyme
2. Inhibiting or stimulating enzymes activity by
the use of allosteric sites
– Not the active site
– Other molecules can interact with/regulate
enzyme activity
– If an activator binds = enzyme is functional
– If an inhibitor binds = enzyme is not functional
Review Questions
Why are enzymes important in biological
processes? Give an example.
What is an enzyme-substrate complex?
Differentiate b/t competitive and noncompetitive inhibition.
Things You Should Know...
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•
•
•
•
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Redox rxns
Acid/Base Buffers
Condensation vs. Hydrolysis Rxn
Role of enzymes
Enzyme substrate complex
Competitive vs. non-competitive inhibition