Download What Are Enzymes?

Apple Experiment
Come down and get an apple and a slice of
lemon.
When you get back to your seat:
1. Take a big bite of your delicious apple.
2. Immediately squeeze lemon juice over the apple flesh
that is now exposed from the bite.
3. IMPORTANT! Don’t get lemon juice all over the apple.
Make sure
that it is ONLY on the area that you just bit!
4. Set the lemon aside and wipe any lemon juice off of
your hands with a napkin.
5. Take another bite from the opposite side of your apple.
6. Set your apple aside.
What Are Enzymes?



Enzymes are
__________ (tertiary
and quaternary
structures).
An enzyme is a
_________ in cellular
reactions.
A catalyst accelerates
a reaction.
Enzymes

Are ________ for
what they will catalyze

Are _________

Usually end in -_____
-Sucrase
-Lactase
-Maltase
How do enzymes work?



Each enzyme has a unique 3-D shape, including a surface groove
called an ______ _____.
The enzyme works by binding a specific chemical reactant
(_________) to its active site, causing the substrate to
become unstable and react.
The resulting __________ is then released from the active
site.
How do enzymes work?
Enzymes work by
_______ ______
which ________
activation energy.
Enzyme-Substrate Complex
The reactant an
enzyme acts on is
specifically called
the _________.
Substrate
Joins
Enzyme
______ _____

A specific region of an enzyme molecule which binds
to the substrate.
Active
Site
Substrate
Enzyme
Shape of a Protein

An enzyme fits
with its
substrate like a
____ and ____.
EnzymeAnimation : Gary E. Kaiser
http://student.ccbcmd.edu/biotutorials/proteins/enzsub.html
View : http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzyme
s_work.html
Enzymes are ____ ________ in the reactions they catalyze.
Think of them as tiny machines in manufacturing.
The more machines, the faster the accumulation of _________.
Image:
Wine Bottling : www.morrison-chs.com/timingscrews/index.html
Wine Vats: www.lymebaywinery.co.uk/pages/about_us.htm
( ________ )
_______ + ________ ----------->
_________
( ________ )
__________ -----------> ________
________
Formats for writing a chemical
reaction.
4 levels of Protein Structure
How Do You Stop
an Enzyme?
_______________
• Alteration of a protein shape
through some form of external stress
• Denatured
protein can’t carry out its
cellular function .
Irreversible egg
protein
denaturation
caused by high
temperature (while
cooking it).
Factors Affecting Enzyme Activity

Temperature

pH

Cofactors & Coenzymes

Inhibitors
Temperature & pH

Think about what kind of cell or organism an
enzyme may work in…

Temperatures far above the normal range
_________ enzymes

(This is why very high fevers are so dangerous. They can cook the body’s
proteins)

Most enzymes work best near __________ pH
(6 to 8).
Coenzymes & Cofactors

Non-protein substances (zinc,
iron, copper, vitamins) are
sometimes need for proper
enzymatic activity.
• Coenzyme versus Cofactor:
What’s the dif?
_________ more general
term. Includes inorganic and
organic molecules.
_________ type of Cofactor,
But specifically organic
molecules.
Image:
EnzymeCofactor : Public domain Wiki, Ribbon-diagram showing carbonic anhydrase II. The grey sphere is
the zinc cofactor in the active site.
Coenzyme : Vitamin B12

Example:
Most _________ are
coenzymes essential in helping
move atoms between
molecules in the formation of
carbohydrates, fats, and
proteins.
• Exclusively synthesized by
___________ (found
primarily in meat, eggs and
dairy products).
Image: VitaminB12 : NIH, Public Domain
www.nlm.nih.gov/.../ency/imagepages/19516.htm
1.
___________ ____________:
Chemicals that resemble an enzyme’s
normal substrate and compete with it for
the active site.
Substrate
Competitive inhibitor
Enzyme
Two Types of Enzyme Inhibitors
1. Competitive inhibitors:
Resemble an enzyme’s normal substrate and compete
with it for the active site.
Image: Competitive Inhibition : www-biol.paisley.ac.uk/.../chapter3_2.html
_______________ ______________:
Do not enter the active site, but bind to another
part of the enzyme causing the enzyme to change
its shape, altering the active site.
Substrate
Enzyme
Noncompetitive
Inhibitor
active site
altered
Two Types of Enzyme Inhibitors
Enzyme Inhibitors
Blocking an enzyme's
activity can kill a
pathogen or correct a
metabolic imbalance.
Many _____ are enzyme
inhibitors.
Enzyme inhibitors are
also used as _________
and __________.
Images
Dead Bug : www.kansas.gov/help_center/user_testing.html
Prescription Drugs : www.patentdocs.us/.../08/by-kevin-e-noon.html
Regulation of Enzyme
Activity
Enzyme activity is regulated by
four different mechanisms*
(1) Allosteric control
(2)Covalent modification
*changes in enzyme levels due to regulation
of protein synthesis or degradation are
additional, long-term ways to regulate
enzyme activity
Allosteric regulation of enzyme
activity
(1) Allosteric regulation = the
activation or inhibition of an
enzyme’s activity due to binding of
an effector molecule at a regulatory
site that is distinct from the active
site of the enzyme
(2) Allosteric regulators generally
act by increasing or decreasing the
enzyme’s affinity for the substrate
Covalent modification
(1) Covalent modification allows an
enzyme to be rapidly activated or
inactivated
(2) With covalent modification, regulation
of a enzyme activity is achieved at low
energy costs to the cell (i.e. regulation
does not require synthesis of a new
enzyme or inhibitory protein).
(3) Phosphorylation is a good example of
how enzymes are activated and
inactivated by covalent post-translational
modifications
Covalent modification regulates the
catalytic activity of some enzymes
Can either activate it or inhibit it by
altering the conformation of the enzyme
or by serving as a functional group in the
active site.
Summary of regulatory mechanisms
(1) Allosteric regulation
ATP activation/CTP inhibition of ATCase
sigmoidal kinetics
cAMP activation of cAMP-dependent protein
kinase
(2) Reversible covalent modification
Phosphorylation
Ser/Thr protein kinases, Tyr kinases,
kinase cascades
Allosteric Enzyme ATCase
Active relaxed form
COOCH2
HN-C-COOHH
COOO CH2
H2N-C- N-C-COOHH
Quaternary structure
R
R
CCC
ATCase
ATP
Catalytic subunits
CCC
R
R
- - -
+
Carbamoyl aspartate
=
=
O
H2N-C-O-PO32-
Aspartate
- - -
Carbamoyl
phosphate
R
R
Regulatory subunits
Catalytic subunits
CTP
CTP
CTP
CTP
CTP
CTP
Inactive tense form
Juang RH (2004) BCbasics
Feedback
inhibition
CTP
Nucleic acid
metabolism
Sigmoidal vo
Curve Effect
Sigmoidal curve
Noncooperative
(Hyperbolic)
ATP
Positive effector (ATP)
brings sigmoidal curve
back to hyperbolic
CTP
Cooperative
(Sigmoidal)
Negative effector (CTP)
keeps
vo
Exaggeration of
sigmoidal curve
yields a drastic
zigzag line that
shows the On/Off
point clearly
Consequently,
Allosteric enzyme
can sense the
concentration of
the environment and
adjust its activity
Off
[Substrate]
On
Juang RH (2004) BCbasics
Mechanism and Example of Allosteric Effect
Kinetics
R = Relax
(active)
Models
Cooperation
Allosteric site
R
vo
(+)
S
S
R
S
[S]
R
A
(+)
vo
S
Allosteric site
S
Heterotropic
(+)
Sequential
X
Heterotropic
(-)
Concerted
T
(+)
R
X
[S]
T
T = Tense
(inactive)
Homotropic
(+)
Concerted
I
vo
(-)
X
(-)
T
T
[S]
Juang RH (2004) BCbasics
Activity Regulation of Glycogen Phosphorylase
Covalent modification
A
P
AA
spontaneously
AMP
Non-covalent
A
Glucose
Caffeine
A
P
P
P
A
P
A
P
A
P
R
P
GP phosphatase 1
ATP
Glc-6-P
Glucose
Caffeine
T
P
GP kinase
A
P
T
A
P
R
Garrett & Grisham (1999) Biochemistry (2e) p.679
A
P