Download ppt - Manning`s Science

+
SBI4U
BIOCHEMISTRY
Enzymes
Ms. Manning
Essential Questions:
1.
What are enzymes and what is their role in
normal cellular function?
2.
What are the chemical structures and
mechanisms of various common enzymes?
3.
What are the factors that affect the
function of enzymes in cellular processes?
4.
Why/how are enzymes used in the food
and pharmaceutical industry?
What
does
this
look
like?
Map of Glucose Metabolism
+
Homework Question:
What is a metabolic
(biochemical) pathway?
What is the role of enzymes in
metabolic pathways?
http://highered.mcgrawhill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032272&showSelfStudyTree=t
rue
+
How are macromolecules brought
into the body converted into
molecules that make up the body?
The body’s metabolism consists of a large
number of biochemical pathways that
consist of sequences of chemical reactions.
convert
substrate molecules into specific
products needed by the body.
+ Types of Biochemical
Pathways
There are two fundamental types of
biochemical pathways.
1.Anabolic
pathways build complex
products from less complex substrates
2.Catabolic
pathways break down
complex molecules to make energy
available for biological processes.
+
Which of these reactions are:
a) anabolic
b) catabolic?
1.
2.
Neutralization (acid-base) reaction
Hydrolysis reaction
3.
Oxidation-reduction (redox) reaction
4.
Condensation (dehydration)
synthesis reaction
+
Enzymes

Proteins (globular structure) that
catalyze chemical reactions

In enzymatic reactions, the molecules
at the beginning of the process are
called substrates, and the enzymes
converts them into different
molecules, called the products
 Why
is an enzyme called a catalyst?
+
Elephant Toothpaste Recipe
Recipe:
- Hydrogen Peroxide
- Soap
2 H2O2  O2 + 2 H2O
What will happen to
the new recipe when
a catalyst is added?
+
Enzyme Characteristics
What characteristic was presented in the demo?

Speed up chemical reactions!
Almost all cellular reactions need
enzymes to occur at significant rates.
Without enzymes, chemical reactions
would still occur, but they would happen
much to slowly to sustain life.
+
How do enzymes work?
http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032270&showSelfStudyTree=true
+
Enzymes in Digestion
+ Enzyme Characteristics
What characteristic was presented
in the lock and key activity?
Enzymes are specific for one
particular reaction or group of
related reactions.

Lactose
(milk sugar)
Lactase
Triglycerides
(lipid)
Lipase
Amylose
(starch)
Amylase
Protein
Protease
+
Homework Question: #3-4, pg. 115
What is the
difference?
+
Homework Question: #1 pg. 115
-
Enzymes called catalysts because they speed
up chemical rxns
-
Interact with substrates to convert them to
products
-
Substrates drawn to active site through weak
bonds
-
Intra-substrate bonds weakened and substrate
is split apart
-
Weakening of intra-substrate bonds by
enzyme makes rxn occur faster
Enzyme Action and the Hydrolysis
of Sucrose
Enzyme sucrase
breaks down a
molecule of
sucrose into
glucose and
fructose
http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032271&showSelfStudyTree=true
+
Homework Question: #2, pg. 115

Catabolic – enzyme breaks substrate
apart – exergonic reaction (yeilds
energy)

Anabolic – enzyme builds larger
substrate by joining two substrates –
endergonic reaction (requires
energy)
+ Enzyme Structure
Hormone-sensitive
lipase
HSL catalyzes the
breakdown of stored fat
Glycerol
The active site of HSL (green)
catalyzes the breakdown of TGs
in a process called Lipolysis.
Adipocyte
(fat cell)
TG
TG
TG
FA
FA
Triglyceride
FA
+ H2O (hydrolysis)
HSL
Glycerol
FA
Contreras J A et al. J. Biol. Chem. 1996;271:31426-31430
©1996 by American Society for Biochemistry and Molecular Biology
FA
FA
Diglyceride
+
Activation Energy and Enzymes
+
What is activation energy?
a) The thermal energy associated with random
movements of molecules
b) The energy released through the active
breaking of chemical bonds
c) The difference in free energy between
reactants and products
d) The energy required to initiate a chemical
reaction
+ Explain the role of activation
energy in a reaction. How does
an enzyme affect activation
energy?
Activation energy  the amount of energy needed to
trigger the reaction.
Without reaching the activation energy, reactions can't
take place.
Enzymes catalyze this process by lowering the amoun
of energy required to activate the reaction.
+
Activation Energy and Enzymes
The amount of activation energy that is required is considerably less
when enzyme is present.
+
Factors that Affect Enzyme
Activity (reaction rate)
Q#1-4 pg. 116 on enzyme worksheet
Enzyme is said
to be denatured
– no longer a
catalyst
Enzyme is said
to be denatured
– no longer a
catalyst
Other Regulators of
Enzyme Activity
Enzyme Cofactors (pg. 117)
Q#1 - Describe the general role of
cofactors in enzyme activity
Non-protein, bound
May
to enzyme
be organic or inorganic ions
Enhance
change
enzyme activity - “helper”
enzyme active site shape
make active site more reactive
Examples of Inorganic Cofactors
Mg in Chlorophyll
Fe in heme group of hemoglobin
Organic Cofactors
Active site
Coenzymes
e.g., NAD
Prosthetic group
(perm. attached)
Active site
Enzyme
Coenzyme
(detaches)
Prosthetic Groups
e.g., FAD
Enzyme
Important Organic Cofactors
Nicotinamide Adenine Dinucleotide (NAD)
coenzyme derived from vitamin B3
Coenzyme
carries and transfers electrons and functions as
oxidizing agent in redox reactions
e.g., NAD
Active site
Coenzyme
(detaches)
Enzyme
Important Organic Cofactors
Flavin Adenine Dinucleotide
(FAD)
Active
site
 prosthetic group
Prosthetic
group
(perm.
attached)
Enzyme
 like NAD, FAD functions as a
reducing agent in cellular
respiration and donates electrons
to the electron transport chain
Prosthetic Group
e.g., FAD
+
Covalent Modulation
 Enzymes
can be activated or inactivated by
covalent modification.
A
common example is phosphorylation of an
enzyme (addition of a phosphate group to the
amino acids serine, threonine, or tyrosine)
mediated by another enzyme called a kinase .
 The
phosphorylation is reversible, and other
enzymes called phosphatases typically catalyze
the removal of the phosphate group from the
enzyme.
+
Enzyme Inhibitors

Enzymes may become deactivated
 Temporarily
or Permanently
Types of Inhibitors
 Reversible
Inhibitors
 Irreversible Inhibitors
+
Reversible Inhibitors

Used to control enzyme activity

Involves the substrate or the end
product of the reaction

For example: a build up of the end
product – called feedback inhibition
http://highered.mcgraw-hill.com/classware/ala.do?alaid=ala_1032273
+
Competitive Inhibitors

Competitive Inhibitors have a similar
shape as the substrate

Compete with the substrate to bind to
the active site, but no reaction occurs

Block the active site so no substrate
can fit
Competitive Inhibition
+
Non-Competitive Inhibitors

Binds to a different site on the enzyme

Does not compete with the substrate to
bind to the active site
Two ways to non-competitively inhibit
the enzyme:
1. slow down the reaction
or
2. changes the shape of the active site
(allosteric inhibition)
Which of the following diagrams represents allosteric inhibition?
(a) Reaction
+
Substrate
enzyme
Inhibitor
site
(b) Inhibition
enzyme
Inhibitor
site
active
site
Substrate binds with
the active site of
enzyme
Reaction occurs and product
molecules are produced
active
site
Inhibitor
Inhibitor binds with the inhibitor Substrate may still bind with the
enzyme but the reaction rate is
site of the enzyme
reduced
(a) Reaction
Substrate
active
site
enzyme
(b) Inhibition
Substrate
Substrate binds with Reaction occurs and product
molecules are produced
the active site of
enzyme
active
site
enzyme
Inhibitor Inhibitor binds with the inhibitor site
of the enzyme and changes the
structure of the active site
Inhibitor prevents binding
of the substrate by
changing the active site
shape
(a) Reaction
Substrate
active
site
enzyme
(b) Inhibition
Substrate
Substrate binds with
the active site of
enzyme
Reaction occurs and product
molecules are produced
active
site
enzyme
Inhibitor Inhibitor binds with the inhibitor site
of the enzyme and changes the
structure of the active site
Inhibitor prevents binding
of the substrate by
changing the active site
shape
(a) Reaction
+
Substrate
enzyme
Inhibitor
site
(b) Inhibition
enzyme
Inhibitor
site
active
site
Substrate binds with
the active site of
enzyme
Reaction occurs and product
molecules are produced
active
site
Inhibitor
Inhibitor binds with the
inhibitor site of the enzyme
Substrate may still bind with the
enzyme but the reaction rate is
reduced
Check for Understanding
Q#2 – Distinguish between competitive
and non-competitive inhibition

Competitive


inhibitor competes with the substrate for binding to the active site of the
enzyme and prevents reaction
Non-competitive

inhibitor does not compete for the active site,

binds to a different site,

either slows down or completely prevents reaction.
Check for Understanding
Q#2 – Explain how allosteric inhibitors
differ from other non-competitive
inhibitors:
 While non-competitive inhibitors
reduce enzyme activity and slow down
the reaction rate, allosteric inhibitors
block the active site altogether and
prevent its functioning completely
+ Irreversible Inhibitors

Also called poisons

For example: certain heavy metals
 E.g., cadmium, lead, mercury
Retained
in the body and lost slowly
Cyanide is a poison that prevents the activity of
cytochrome C oxidase, an enzyme in the electron
transport chain in the cell. It therefore inhibits ATP
production and cellular respiration.
Cytochrome c oxidase
+
Why are enzymes so tightly
regulated by co-factors and
inhibitors?
+ Control of Metabolism
 Biochemical
reactions are controlled in part by the
specificity of substrate biding, but the human body
could not function if all enzymes were present together
and all operating maximally with no regulation.

There would be biochemical chaos with substances
being synthesized and degraded at the same time.
 Instead, the
body tightly regulates enzymes through
metabolic pathways and by controlling specific
enzymes within a pathway.
 This
approach allows an entire pathway to be turned on
or off by simply regulating one or a few enzymes.
 Metabolic
pathways can also be regulated by switching
specific genes on or off.
+
Why is it important to know how
enzymes are regulated?

Enzymes play a critical role in everyday life. Many heritable
genetic disorders occur because there is a deficiency or total
absence of one or more enzymes.

Other disease conditions (e.g., cancer) result because there
is an excessive activity of one or more enzymes.

Routine medical tests monitor the activity of enzymes in the
blood, and many of the prescription drugs (e.g., penicillin,)
exert their effects through interactions with enzymes.

Enzymes and their inhibitors can be important tools in
medicine, agriculture, and food science.
Test study tip:
Create
a concept map that summarizes
the regulation of enzyme activity
Include the following terms:
temperature
Active site
Co-factors
pH
Enzyme inhibitors
Co-enzymes
Enzyme
concentration
Competitive
inhibitor
Allosteric inhibitor
Substrate
concentration
Non-competitive
inhibitor
Irreversible
inhibitors
denature
Inhibitor site
Enzyme reation
rates
Reversible
inhibitors