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Globular proteins Precise 3D shape Multiple chains Hydrophilic R groups on outside = water soluble Active site: region on an enzyme to which another molecule/molecules- called a substrate- can bind Enzymes
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EnzymesINB Pg 20
Enzymes are protein molecules that act as biological catalysts Catalyst: molecule that speeds up a chemical
reaction and remains unchanged after rxn Enzymes usually end in –ase Virtually every metabolic rxn is catalyzed by
an enzyme
Enzymes
Globular proteins Precise 3D shape Multiple chains Hydrophilic R groups on outside = water soluble
Active site: region on an enzyme to which another molecule/molecules- called a substrate- can bind
Enzymes
Idea that enzyme has a particular shape to which the substrate fits exactly Substrate=key. Held in place by temporary bonds Enzyme=lock
Lock and Key Hypothesis
Each type of enzyme will act on only one type of substrate molecule Shape of active site will only allow one
shape to fit Enzyme is said to be specific for substrate
Lock and Key Hypothesis
Modified the lock and key hypothesis in 1959 New evidence suggested that enzymes are
more flexible than is suggested by a rigid lock and key
Basically same as lock and key, but adds the idea that the enzyme, and sometimes substrate, changes shape slightly as substrate enters enzyme
Induced Fit Hypothesis
Ensures a more perfect fit Makes catalysis more efficient http://www.youtube.com/watch?v=z8lG8X9Z
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Induced Fit Hypothesis
An enzyme may catalyze a reaction in which it joins together two peptides (synthesis)
An enzyme may catalyze
a reaction in which the substrate molecule is split into two or more molecules (catalysis/decomposition)
Catalysis and synthesis
Enzyme-product complex is briefly formed before the release of products
Interaction between the R groups of the enzyme and the atoms of the substrate can break, or encourage formation of, bonds in the substrate molecule, forming products
When the rxn is complete, the products leave the active site Enzyme is unchanged and ready to accept another
substrate Rate of rxn is extremely rapid
Catalysis
Found in tears, saliva, and other secretions. Breaks the polysaccharide chains in the cell walls of bacteria
http://www.youtube.com/watch?v=QXIe0jDTlT4
Lysozyme
As catalysts, enzymes increase the rate at which chemical reactions occur
Most of the rxns in living things would be too slow w/o an enzyme to sustain life
Enzymes
Energy needed to start reaction = activation energy Enzymes work by lowering activation energy
Chemical Reactions
Increase concentration of substrate Increase energy of reactants (heating)
Ex: Benedict’s test Most rxns occur at temps higher than our
body temp, which is why enzymes are necessary
Other ways to increase rxn rate
When enzyme and substrate are first mixed, there are a large number of substrate molecules
At any moment, virtually every enzyme molecule has a substrate in its active site
The course of a reaction
Initially, the rate at which a reaction occurs will depend only on how many enzyme molecules there are and the speed at which the enzyme can convert substrate into product
However, as more substrate is converted to product, there are fewer and fewer substrate molecules, which slows down the rate of reaction
The course of a reaction
Directly proportional to reaction rate As we increase the
concentration of an enzyme, we have more active sites available for the substrate.
As long as there is plenty of substrate available, the initial rate of reaction increases linearly with enzyme concentration
The effect of enzyme concentration
As concentration of substrate increases, the initial rate also increases
If we continue increasing substrate concentration, it will eventually max out because there are no more available active sites If more substrate is added,
the enzyme simply cannot work faster. The enzyme is working at its maximum possible rate, known as Vmax (V=velocity)
The effect of substrate concentration
Low temp=low particle movement. Substrate move very slowly and will not often collide with the active site
As temp increases, substrates move faster and collide with active site more. Reaction rate increases
At a certain temperature (specific for diff. enzymes), hydrogen bonds begin to break in the enzyme (remember, it is a protein) and the enzyme will denature (loose its structure and function)
Temperature and enzyme activity
Denaturing of an enzyme is often irreversible Substrate cannot fit into denatured active
sites, so no activity takes place The temperature at which an enzyme
catalyzes a reaction at the maximum rate is called the optimum temperature
Temperature and enzyme activity
pH is a measure of hydrogen ions in solution. The lower the pH, the higher the hydrogen ion solution.
Hydrogen can interact with R groups of amino acids which affects bonding in amino acids, which can change the structure (and function) of an enzyme
Enzymes work best under specific pH ranges.
pH and enzyme activity
Proteases (enzymes that break down proteins) are used in biological washing powders. How would a protease remove a blood stain on
clothes? Most biological washing powders are recommended
for use at low washing temperature. Why is this?
Check your understanding
Hemoglobin is the colored pigment that causes blood stains. Protein-digesting enzymes hydrolyze hemoglobin to amino acids, which are colorless. They are also soluble, so will wash away in water.
Many protein-digesting enzymes have an optimum temperature of around 40 °C. If the temperature of a reaction is too high, the enzyme will denature.
Check your understanding