Transcript Biochemical Reactions Chapter 1.3 McGraw-Hill Ryerson Biology 12 (2011) Neutralization • Acid: substance that produces hydrogen ions when dissolved in water – Increases [H+] in aqueous.

Biochemical Reactions
Chapter 1.3
McGraw-Hill Ryerson
Biology 12 (2011)
Neutralization
• Acid: substance that produces hydrogen ions
when dissolved in water
– Increases [H+] in aqueous solution
• Base: substance that produces hydroxide ions
when dissolved in water
– Increases [OH-] in aqueous solution
Neutralization
• pH scale: measures relative concentration of
[H+] ions in aqueous solution
Neutralization
• Neutralization reaction: When acid and base
react
– Produces a salt and water
Neutralization
• Buffers: substances that resist changes in pH
by donating or accepting hydrogen ions as
needed
– Buffers require their reactions to occur in both directions
(i.e. must be able to reverse)
– Human blood pH ranges from 7.35-7.45; carbonic acid is a
buffer present in blood to maintain this pH
Oxidation-Reduction Reactions
• Oxidation: When molecules loses electrons
– but electrons are highly reactive and do not exist on their own/freely
– Thus another molecule must complement the reaction by receiving electrons…
• Reduction: When molecules gains electrons
Reactions are labelled redox reactions because they
occur simultaneously
Examples of redox reactions: cellular respiration, iron rusting, combustion
•
“LEO goes GER”
– LEO – Losing Electrons: Oxidation
– GER – Gaining Electrons: Reduction
Condensation and Hydrolysis
• Condensation: reaction forms a covalent bond between two
molecules with production of a water molecule
• Hydrolysis: reaction that cleaves a covalent bond by adding a
water molecule
*Present in polymerization of sugars, lipids,
amino acids, and nucleic acids*
Enzymes
• Enzymes are protein molecules that act as
catalysts
– Speeds up chemical reactions in the body
• All chemical reactions require energy to start
– Referred to as Activation Energy (Ea).
Enzymes
• Enzymes work by lowering the activation
energy (Ea) of a reaction
– As a result, the reaction goes FASTER because less energy is
required for it to begin
Enzymes
• Heat usually provides the source for activation
energy in many chemical reactions
– Increase in temperature can increase rate of most reactions
• But proteins denature at high temperature…
– Thus cells use enzymes to promote reactions
Enzymes
• Enzymes have unique optimal temperature
and/or optimal pH where they work best
e.g. protease work best at acidic pH (present in the stomach)
Enzymes
• There are many different types of enzymes,
each one specific to a specific job
– Names are usually associated with its job, usually
ending with ‘ase’
• e.g. Enzyme in our saliva is amylase to break down
amylose and amylopectin (starch) into simple sugars
Enzymes
• Components of an enzyme-reaction
– Substrate: the reactant which the enzyme acts on
• Enzymes bind to substrate to convert it into a product
– Active site: the location where the substrate binds
• Active sites are specific for a particular substrate
Enzymes
Induced Fit Model: After a substrate binds to the
active site, the enzyme slightly changes shape to
better accommodate the substrate
Enzymes
• Weak bonds with the R-groups of the amino acids in the
active site hold the substrate in place
• Enzymes lower the activation energy by binding substrates
together in the correct orientation and by applying stress to
the substrate’s bonds, reducing the amount of thermal energy
that must be absorbed to achieve transition state
• Active sites can also provide suitable microenvironments for
particular reactions (e.g. can provide alternate pH levels
depending on the amino acids present in the active site)
Enzymes
• Once the reaction is complete the product is
released from the enzyme and the enzyme is free to
accept another substrate and conduct the reaction
again
– Referred to as Catalytic Cycle
Enzymes
• Sometimes enzymes require the presence of
additional molecules to catalyze the reaction
– Coenzymes: organic molecules that assist an enzyme
– Cofactors: metal ions that assist the enzyme
Either of these may bind to active site or substrate
e.g. vitamins are coenzymes
Enzymes
• Enzyme activity can be
regulated
• Activator: molecule that binds to
allosteric site of an enzyme to
keep it active or cause increase in
activity
Allosteric site: site on enzyme that is
not the active site but allows interaction
with molecules to change activity
Enzymes
• Enzyme activity can be
regulated
• Inhibitors: chemicals that
interfere with enzyme function
• Competitive Inhibition: Could
bind to active site, preventing
substrate from entering (thus
“competing” with substrates for
active sites)
• Noncompetitive Inhibition:
Could bind to allosteric site
which changes the shape of the
enzyme, causing the active site
to change, preventing substrate
from binding
Enzymes
• Enzyme activity can be
regulated
• Biochemical reactions
usually occur in pathways
(multi-step reactions to
change reactant into
product)
• Feedback inhibition: the
final product is an inhibitor
of the enzyme that
catalyzes the reaction
Homework
• Pg 42
• #1, 3-12