Transcript What is an enzyme - Winona State University

Enzymes-What are they and How do
they work? 9/7 and 9/9
Don’t forget to work on the problems at end of
yesterdays notes
 What happens to Keq in a complicated rxn?
 What happens when we run out of energy?
 What is an activation energy?
 What is an enzyme?
 What do enzymes do and under what conditions?
 How do enzymes stabilize the intermediate?
 What is Michaelis-Menton Kinetics?
What happens to Keq when the number of product or reactant
molecules in a reaction is not 1:1?
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Simple Old Fashion Rxn: Hexokinase
Glucose + ATP  G-6-P + ADP
Keq = [G-6-P][ADP]/[Glucose][ATP]
Complicated Reaction? Example catalase
H2O2 + H2O2  2 H2O + O2
Keq= products/reactants or keq= [O2]/ [H2O2]2 …..
Note: product or reactant concentrations are now factored
to the n-th power or (P)n !!!!
Remember that water is ignored because its presence in
the solution is 56 M
This won’t be on tests but might be useful on a GRE exam!
If the disorder of the universe is constantly increasing, how do cells
continue to survive?
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Cells live if they have energy!
Cells get energy from the sun, chemosynthesis or other
cells/cell-products!
Heterotrophs use other organisms!
Cells store energy: fats, carbohydrates and proteins
What happens when cells die or get injured?
1) ATP supply too low!
2) Pumps don’t work!
3) Ions flow in/out!
4) Water flows in and cells swell/become fragile!
5) Cell may incur temporary OR permanent damage!
Correlation of fish removed from water?
Correlation to person experiencing a stroke?
What happens to energy during a chemical reaction? ATP Pi + ADP
What is an activation energy? Why do enzymes speed up reactions?
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ATPase
ATP
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1) Activation energy
must be overcome for
Rxn to proceed!
2) Enzymes lower
Activation energy!
3) Enzymes stabilize
transition state!
4) Enzymes make it
easier to get to
energy YIELDING
phase of rxn!
ADP + Pi + Energy
What is an enzyme (….-ase)?
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Enzymes are proteins! (very rarely RNA)
Amino acids use specific charges at the active
site to stabilize the transition state!
Stabilization “lowers” activation energy!
A stabilized transition state makes it easier for
a reaction to rapidly proceed to products!
Enzymes are called “CATALYSTS”
Enzymes often require co-enzymes or
prosthetic groups for activity!
Each enzyme has a specific set of conditions
where it has the most efficient function!
Conditions Affecting Enzymes:
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pH, Temperature, ions around it, etc!
There are 20 different amino acids to chose from in a protein. Peptide bonds link the
A.A. together in chains! These are the charges that line active sites on enzymes.
What do enzymes do?
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Enzymes make 99% of our reactions possible!
Enzymes like carbonic anhydrase increase
reaction rates by up to a 36 X 106 times!!!
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Enzymes are tightly controlled by the cell!
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Enzymes are controlled with respect to access
to coenzymes, pH, temperature, transcription,
translation, chemical modification and by
inhibitors/stimulants!
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HOW??????
How might drugs work?????
Enzymes have group and substrate specificity!
Classic: Environmental pH and Temperature turn enzymes
On/Off or they can permanently disable (denature) an
enzyme. Enzyme have “OPTIMAL” conditions for function!
Two models have been proposed for how enzymes function: The
older ‘Lock and Key’ and newer ‘Induced Fit’ Models.
Induced Fit at the active site leads to substrate activation by the
amino acids and prosthetic groups (if present) of the enzyme!
There are two classic ways that enzymes function as a “substitute”
binding site to stabilize the intermediate: Nucleophilic (e-) or
Electrophilic (p+) substitution, where an electron or proton is given
to the target to promote substrate modification/cleavage.
The active site of carboxyl peptidase (a digestive enzyme) uses a
zinc ion (prosthetic group) to orient/stabilize a target protein so it
can be cleaved precisely between glycine-tyrosine peptide bonds.
In this example the digestive enzyme chymotrypsin is breaking the
peptide bond on its substrate into two pieces (products)! This is
done by stabilizing the formation of an acyl-intermediate that is
temporarily attached to the enzyme itself!
Enzymes can catalyze reactions where a reactant turns into
a product, they can also do activities such as carry oxygen
or move glucose across a membrane.
Classic Examples of “enzymes” that do not
have a reactant and product:
 1) Hemoglobin in a erythrocyte
 2) Albumin in plasma
 3) Na+/K+-ATPase
 4) Acetycholine receptor on a neuron
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Any or all of these can be effected by
inhibitors
 Any or all of these can be effected by
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Why does hemoglobin release more oxygen in active muscle and pick
up more oxygen in a pH basic lung????????? Bohr Effect
The shift in the oxygen binding curve to the right means less oxygen will be attached to the
hemoglobins in an acidic region! So oxygen leaves the hemoglobin and can be delivered to
where it is needed most! ↑Carbon dioxide and ↑Temperature have similar effects.
If the Hb is not bound by oxygen you will appear cyanotic (bluish)!
Remember that only a tiny amount of oxygen can dissolve directly in
blood! (see bottom yellow line) The more hemoglobin you have in
your blood, the more oxygen your blood can deliver (that simple)!
If the tissues are warmer or more acidic, the oxygen is more likely to
leave the hemoglobin so it can be used in this tissue (that simple).
Shift occurs if pH↓ or Temp. ↑