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UNIVERSITY OF MICHIGAN
Exam 1 Study Guide Enzymes,
DNA Sequencing, and
Statistical Analysis
Course: BIOL 173 BIOLOGY LAB
, -What are Enzymes? Proteins that catalyze biological reactions. Proteins mean they are made of
polypeptide chains. They have a complicated 3D structure, which is crucial to function. Catalyzing means
they make reactions go faster while not being consumed in the reactions. There are RNA catalysts called
ribozymes.
-How do enzymes work? The substrate binds to the enzyme in the active site. Induced fit- enzyme
changes shape slightly. The enzyme lowers the activation energy of a reaction and allows the substrate to
become a product more easily.
-Complementary shape if crucial to function. Enzymes are particular because of their shape. Because of
their shape, they can only act on one substrate and carry out one reaction. When the substrate binds,
interactions between the substrate and protein will change the shape of the protein slightly (induced fit). A
few amino acid side chains (or cofactors) protrude into the active site and catalyze the reaction.
-How do we measure enzyme function? Determine the rate of enzyme action. Measure the amount of
substrate converted into product per unit time. Follow increase (product) or decrease (substrate). Must
have an easy way to detect and quantify. Spectrophotometry- measurement of absorbance of light.
Absorbance is proportional to the compound.
-What effects rate? Substrate and enzyme. Product. Temperature and pH. The inherent efficiency of the
enzyme. Reaction order. Factors that affect enzyme shape.
-How do we get enzymes? Extract and purify them from the cell. Homogenization- blending tissue,
breaking cells. Centrifugation- separating different compounds. Purify- as much as needed.
-What enzyme are we studying? Polyphenoloxidase.
-Scientific Method: What is your hypothesis? Make a prediction. Experimental design- what is your
control? Analyze data: Plot product vs time, initial rate vs substrate. Report results.
-Effect on enzyme and substrate: In a simple chemical reaction, if reactants are doubled then the reaction
rate doubles. Rate depends on the concentration of both enzyme and substrate. Rate determined by
whichever is limiting (usually enzymes because you should use the bare minimum of enzymes because if
you have a ton, the reaction will be out of control).
Vmax=The maximum rate of reactions, at this time all active sites are occupied.
Km= The substrate concentration at which reaction rate is half maximal. Km will vary with conditions
and is used as a measure of the affinity of enzyme for substrate. The lower the Km, the more likely an
enzyme id to be operating at its vmax. Higher vmax is better, lower Km is “better.”
-The rate is figured out from Absorbance vs Time graph. The Vmax and Km are dteermined by rate vs
substrate graph
Enzymes have optimal conditions for functioning. Anything that distorts shape will reduce function
Many enzymes require cofactors. Cofactors are non-protein enzyme helpers. May be inorganic (such as a
metal ion) or organic (coenzyme, like vitamins). Cofactors may help bind or position the substrate; may
help with catalysis.
Competitive inhibition: A molecule with a similar shape as the substrate competes for access to active site
-Active sites being occupied by competitive inhibitors does not lead to a productive reaction. This
“wastes” the enzymes time and lowers the rate of the true reaction
Competitive inhibition: Vmax will be the same, Km will be higher because it takes a higher substrate
concentration to get the same rate of product formation (or same proportion of active sites filled by
substrate). Inhibitor has less effect at high substrate concentrations. % inhibition depends on enzyme,
inhibitor, and substrate
UNIVERSITY OF MICHIGAN
Exam 1 Study Guide Enzymes,
DNA Sequencing, and
Statistical Analysis
Course: BIOL 173 BIOLOGY LAB
, -What are Enzymes? Proteins that catalyze biological reactions. Proteins mean they are made of
polypeptide chains. They have a complicated 3D structure, which is crucial to function. Catalyzing means
they make reactions go faster while not being consumed in the reactions. There are RNA catalysts called
ribozymes.
-How do enzymes work? The substrate binds to the enzyme in the active site. Induced fit- enzyme
changes shape slightly. The enzyme lowers the activation energy of a reaction and allows the substrate to
become a product more easily.
-Complementary shape if crucial to function. Enzymes are particular because of their shape. Because of
their shape, they can only act on one substrate and carry out one reaction. When the substrate binds,
interactions between the substrate and protein will change the shape of the protein slightly (induced fit). A
few amino acid side chains (or cofactors) protrude into the active site and catalyze the reaction.
-How do we measure enzyme function? Determine the rate of enzyme action. Measure the amount of
substrate converted into product per unit time. Follow increase (product) or decrease (substrate). Must
have an easy way to detect and quantify. Spectrophotometry- measurement of absorbance of light.
Absorbance is proportional to the compound.
-What effects rate? Substrate and enzyme. Product. Temperature and pH. The inherent efficiency of the
enzyme. Reaction order. Factors that affect enzyme shape.
-How do we get enzymes? Extract and purify them from the cell. Homogenization- blending tissue,
breaking cells. Centrifugation- separating different compounds. Purify- as much as needed.
-What enzyme are we studying? Polyphenoloxidase.
-Scientific Method: What is your hypothesis? Make a prediction. Experimental design- what is your
control? Analyze data: Plot product vs time, initial rate vs substrate. Report results.
-Effect on enzyme and substrate: In a simple chemical reaction, if reactants are doubled then the reaction
rate doubles. Rate depends on the concentration of both enzyme and substrate. Rate determined by
whichever is limiting (usually enzymes because you should use the bare minimum of enzymes because if
you have a ton, the reaction will be out of control).
Vmax=The maximum rate of reactions, at this time all active sites are occupied.
Km= The substrate concentration at which reaction rate is half maximal. Km will vary with conditions
and is used as a measure of the affinity of enzyme for substrate. The lower the Km, the more likely an
enzyme id to be operating at its vmax. Higher vmax is better, lower Km is “better.”
-The rate is figured out from Absorbance vs Time graph. The Vmax and Km are dteermined by rate vs
substrate graph
Enzymes have optimal conditions for functioning. Anything that distorts shape will reduce function
Many enzymes require cofactors. Cofactors are non-protein enzyme helpers. May be inorganic (such as a
metal ion) or organic (coenzyme, like vitamins). Cofactors may help bind or position the substrate; may
help with catalysis.
Competitive inhibition: A molecule with a similar shape as the substrate competes for access to active site
-Active sites being occupied by competitive inhibitors does not lead to a productive reaction. This
“wastes” the enzymes time and lowers the rate of the true reaction
Competitive inhibition: Vmax will be the same, Km will be higher because it takes a higher substrate
concentration to get the same rate of product formation (or same proportion of active sites filled by
substrate). Inhibitor has less effect at high substrate concentrations. % inhibition depends on enzyme,
inhibitor, and substrate
