Enzymes
Sections 5.1-5.9 in
Concepts and Connections
We couldn’t live with out them!.....
And we die if they get messed up!
Chemical Reactions
• Before we talk about enzymes…. We need to
discuss chemical reactions.
• A chemical reaction:
– Involves rearrangement of atoms/bonds
– Reactants are changed into products
– Reactants are on the left
– Products are on the right
Ex.
A + B

C + D
reactants
products
Chemical Reactions
• There are four types of reactions:
– Synthesis
– Decomposition
– Single Replacement
– Double Replacement
Practice: Identify reactants and
products
Practice: Identify reactants,
products and type of reaction
Reactants
Products
Practice: Identify reactants,
products and type of reaction
Reactants
Products
Many molecules contain energy
• Energy (E) is the capacity to do work.
• Chemical energy is the potential energy of molecules.
– This is the most important type of energy for living organisms
• During photosynthesis sun E is stored as chemical E
• This energy is used by organisms during cellular respiration.
• Endergonic - chemical reaction that requires energy input
• Ex. photosynthesis
• Exergonic – chemical reaction that releases energy
• Ex. Cellular respiration
Exergonic vs. Endergonic
Ex. Lighting gasoline
Ex. Dissolving salt in water
The cell uses ATP as energy
currency
• Adenosine triphosphate (ATP) is the cell’s
supply of energy.
• ATP is like money in a checking account
– Available right away wherever needed.
– But only limited supply
• ATP is a nucleotide
What is an enzyme?
• Known as a biological catalyst
• Catalyst is something that speeds up a chemical
reaction
• Enzymes speed up reactions in living cells by
lowering energy barriers
• So reactions happen faster, and with less ATP
Enzymes LOWER Activation Energy
• ACTIVATION ENERGY (EA) - the energy
required for a reaction to begin
Uncatalysed reaction
Energy
Catalysed reaction
Reactants
Products
Progress of reaction
Imagine Jumping Beans (pg76)
Or building a snowman… on a hillside
Enzymes
• Most essential reactions of metabolism occur
quickly and precisely for the cell to survive.
• The cell could die before it gets enough jumping
beans or snowballs (cellular products)
• Without enzymes, many metabolic reactions
would occur too slowly to sustain life
Properties of Enzymes
• They are made of PROTEIN
• Reusable - they are not changed by the
reactions they speed up
• They are specific - means that only one
particular enzyme will work with one
particular substrate
Shape is Essential!
• Like all proteins, enzymes have a unique
3-dimensial shape. (globular)
• The shape determines which chemical reaction
the enzyme catalyzes.
• Each enzyme can only perform a few types of
reactions
• ….. So there are thousands of enzymes in a cell!
Enzymes are specific!
• Substrate – the substance that the enzyme works on
e.g. Amylase the substrate is starch
• Product – the substance that is made by the reaction
e.g. Breakdown of starch by Amylase the product
is Maltose
• Active site – the part of the enzyme that actually
binds the substrate.
– The shape of this pocket/groove determines what
substrates an enzyme acts upon.
Enzymes are specific!
• Each enzyme only catalyzes one, or a specific few
types of reactions.
• Enzymes are named using the suffix –ase
• Examples:
–
–
–
–
–
–
Lipase – hydrolyzes (breaks down) lipids
Protease – hydrolyzes proteins (proteolysis)
Amylase – hydrolyzes starch
Sucrase – hydrolyzes sucrose into fructose and glucose
Catalase – decomposition of H202 into water and O2
ATP synthase – synthesizes ATP
CATALASE
• Found in animal and plant cells
• Needed to speed up the breakdown of
HYDROGEN PEROXIDE
• Breaks it down to OXYGEN and WATER
• The word equation for this looks like this
OXYGEN AND WATER
HYDROGEN PEROXIDE
CATALASE
HPCOW
CATALASE
Sucrase
• Found in small intestine
• Break down enzyme
• Breaks SUCROSE down to GLUCOSE
AND FRUCTOSE
• Word equation looks like this
GLUCOSE + FRUCTOSE
SUCROSE
SUCRASE
SSGF
Sucrase
Amylase
•
•
•
•
Found in saliva and in the pancreas
Break down enzyme
Breaks STARCH down to MALTOSE
Word equation looks like this
STARCH
MALTOSE
AMYLASE
SAM
Amylase
Potato Phosphorylase
• Synthesis enzyme (puts together)
• Builds Glucose-1-Phosphate molecules
into Starch
• The formation of starch is tested using
iodine solution
Starch
Glucose-1-Phosphate
Phosphorylase
G1PPS
Potato Phosphorylase
More about Specific
• This means amylase will only breakdown
starch
• Catalase will only breakdown hydrogen
peroxide
• Amylase will NOT breakdown hydrogen
peroxide
• Catalase will NOT breakdown starch
Lock and Key
• All enzymes have a special shaped area
that fits onto their substrate
• This area is called the ACTIVE SITE
• This Active site will fit onto the substrate
while the reaction takes place
• Because it fits like a lock and key we call
this the lock and key mechanism
Model of Lock and Key
substrate
products
enzyme substrate complex
active site
enzyme
enzyme – unchanged
Inducted Fit hypothesis
1. active site is empty
2. Sucrose enters….
“Induced fit” –
enzyme changes
shape and facilitates
reaction
3. Substrate is
converted to
products glucose
and fructose
4. The enzyme releases
products and is
unchanged
Sucrase, pg 77