Transcript enzyme - share1

Enzymes
- What is an enzyme...?
- What do they do?
- How do they work?
- What affects the reaction rate?
- How are enzymes controlled?
- Any examples?
Refer to chapter 3 in text.
- What was an enzyme...?
Enzymes are a class of proteins.
They are polymers of ______.
(How many different ones?)
[How is this sequence determined?]
Differences in R groups affect protein structure how?
reference the levels of structural complexity...
(What is an “R group”?)
Enzymes:
What do they do?
-Any metabolic reaction
(catabolic or anabolic)
that isn’t spontaneous has an
activation energy:
The energy to get it going could be
thermal, mechanical (pressure)…
- Extreme pH can cause the break
of molecular bonds...
Is a body a good place
for fluctuations like these?
Enzymes lower the activation
energy, and ensure specificity.
(Endothermic reactions need to
be linked to an energy source)
- You have learned several
pathways and cycles, most steps
catalyzed by enzymes.
ghs.gresham.k12.or.us/.../notes/chpt8/chpt8.htm
The ‘lock-and-key’ model of enzyme function How do they work?
- Only certain things fit the active site:
accounts for enzyme-substrate specificity
Refinement to lock-and-key - The 3D configuration shifts when the substrate enters,
allowing some range in specificity
(some are more selective than others), and
causing stress that lowers the activation energy:
induced-fit model of enzyme action
NB - The enzyme is not consumed in the reaction.
ghs.gresham.k12.or.us/.../notes/chpt8/chpt8.htm
- What affects the reaction rate?
To some extent increased temperature
speeds reactions up
(more collisions between
enzyme and ligand),
but too much thermal energy will
denature the protein
(causing it to lose its specific
2o, 3o and 4o structure,
and therefore its active site
and enzymatic properties).
pH extremes will also denature proteins
by interfering with the hydrogen bonds.
Each enzyme has its optimal
temperature and pH.
If you add more substrate, the reaction rate increases
(more reactant is running into the catalyst),
but only up to a point.
Once all of the enzymes are busy
adding more substrate can’t make it go faster –
The reaction rate plateaus:
- How are enzymes controlled?
A competitive inhibitor is one that simulates the intended substrate:
- it generally reversibly blocks the active site, so
- high substrate concentration negates the inhibition.
commons.wikimedia.org/wiki/Image:Competitive_...
http://www.columbia.edu/cu/biology/courses/c2005/hand04.html
http://en.wikipedia.org/wiki/Xanthine_oxidase
… An example of a substrate
and a competitive inhibitor.
Here is the enzyme ↖
(The yellow are
molybdenum
cofactors in the
active site, the orange
are Fe-S clusters
for e- transfers.)
A couple medical examples of competitive inhibitors
Ethylene glycol,
in antifreeze
apparently tastes sweet
to kids and pets...
Ethanol reduces its being
converted into oxalic acid,
the really toxic agent,
that affects CNS, heart,
and kidneys.
Another example: Ethanol is metabolized in the body by oxidation to acetaldehyde,
which is in turn further oxidized to acetic acid by aldehyde oxidase
enzymes. Normally, the second reaction is rapid so that acetaldehyde does not
accumulate in the body.
A drug, disulfiram (Antabuse) inhibits the aldehyde oxidase which causes the
accumulation of acetaldehyde with subsequent unpleasant side-effects of nausea and
vomiting. This drug is sometimes used to help people overcome the drinking habit.
http://www.elmhurst.edu/~chm/vchembook/573inhibit.html
In contrast, a noncompetitive inhibitor binds somewhere else
on the enzyme,
which alters the active site and its ability to bind the substrate.
- This is generally irreversible, and
- generally found in toxins, like sarin, DDT, and penicillin.
www.bio12.com/ch6/RemedialEnzymes.htm
Functioning much like noncompetitive inhibitors,
allosteric inhibition and allosteric activation
are a part of normal metabolic regulation.
-These are reversible.
- e.g. ADP enhances the activity of some enzymes
working in catabolism,
and ATP reduces it. (Think it through.)
[When Hb binds O2 at one site the other sites are enhanced.]
www.mindcreators.com/.../ProteinRegulators.htm
These curves can help interpret the action mechanism of a potential drug:
http://onlinebiochemistry.com/obj-512/Chap9-enzymeinhibition.html
Feedback inhibition aka
end-product inhibition
is an example of allosteric
inhibition:
The product of a pathway
goes back and blocks an
early step in the pathway.
This keeps the cell from making
something it already has.
This is from your text →
Some enzymes can’t work alone.
Cofactors come in two types:
Permanently bonded prosthetic groups
like the heme- group in a cytochrome ↓
or reversibly held coenzymes
like many vitamins,
or [acetyl-] CoA ↓.
library.med.utah.edu/.../FattyAcids/2_4.html
www.detectingdesign.com/methinksitislikeaweas...
Enzymes can be extracted commercially,
or their genes can be inserted into bacteria for mass production.
Enzymes have many industrial uses:
Isomerases: switch glucose into
sweeter fructose.↓
Cellulases to produce
“stone-washed” jeans.→
←Pectinase: makes fruit juice
sweeter and less cloudy.
Proteases and lipases
in detergents.
Lactase: makes milk digestible for the lactose intolerant,
and makes ice cream sweeter and smoother.
http://commons.wikimedia.org/wiki/File:Lactase_map2.jpg
It can be immobilized
(attached to a solid material)
for easier removal and reuse.
http://turqase.com/static/images/enzyme_immobilisation.png
Where is this most needed?
Where is this most available?
“Use
of databases to identify potential new anti-malarial drugs.”
Not entirely sure what they want you to do here,
but lifting from Wikipedia (not scientific source)
for ‘anti-malarial medications’:
•1 Medications
• 1.1 Quinine and related agents
• 1.2 Chloroquine
• 1.3 Amodiaquine
• 1.4 Pyrimethamine
• 1.5 Proguanil
• 1.6 Sulfonamides
• 1.7 Mefloquine
• 1.8 Atovaquone
• 1.9 Primaquine
• 1.10 Artemisinin and derivatives
• 1.11 Halofantrine
• 1.12 Doxycycline
• 1.13 Clindamycin
•2 Resistance
• 2.1 Spread of resistance
• 2.2 Prevention
•3 Combination therapy
• 3.1 Non-artemisinin based
combinations
• 3.2 Artemisinin-based combination
therapies (ACTs)
• 3.3 Other combinations
•4 By type of malaria
• 4.1 Falciparum malaria
• 4.2 Vivax malaria
•5 See also
•6 References
•7 External links
Explain competitive vs. noncompetitive inhibition
of enzymes, with examples.
What is denaturation?
What causes it?
What is an active site?
What is an allosteric site?
Compare and contrast the models of enzyme function:
lock-and-key vs. induced fit.
Describe and exemplify
feedback inhibition.
Explain 2 examples of
industrial use of enzymes.
What does an enzyme do?
enzyme activity
enzyme activity
* The effect of pH and temperature were studied for an enzyme-catalyzed
reaction. The following results were obtained.
Temperature
pH
a. How do (1) temperature and (2) pH affect the activity of this enzyme?
Include in your answer a description of the relationship between structure
and function of this enzyme, as well as a discussion of how structure and
function of enzymes are affected by temperature and pH.
b. Describe a controlled experiment that could have produced the data shown
for either temperature of pH. Be sure to state the hypothesis that was tested.
enzyme
metabolic
catabolic
anabolic
catalyzed
enzyme-substrate specificity
lock-and-key
induced-fit
denature
reaction rate
competitive inhibitor
noncompetitive inhibitor
allosteric inhibition
allosteric activation
feedback inhibition
end-product inhibition
cofactor
prosthetic group
coenzyme
lactase
Immobilized enzyme