LECTURE: ENZYMES
LECTURE: ENZYMES KIRSTIN BROWN
Lecture: ENZYMES Outline: 1. Reactions Catalysts o Activation energy o pH and temperature
o Other requirements for enzymes
2. Enzyme Regulation o Competitive inhibitors o Non-competitive inhibitors o Allosteric regulation
Enzymes as Catalysts Activation Energy o A spontaneous reaction (negative ∆G) may
be very, very slow
o Enzymes are catalysts increase the rate of
reactions by lowering the activation energy
o The reactants in an enzyme-catalyzed
reaction are called substrates
Enzymes as Catalysts Activation Energy o The substrate binds to the active site of the
enzyme
o The enzyme stabilizes the transition state by
tightly binding to it
Enzymes as Catalysts Activation Energy o The substrate binds to the active site of the
enzyme
o The enzyme stabilizes the transition state by
tightly binding to it
➢ An intermediate between the substrate
and the product energy of activation required to reach transition state
Enzymes as Catalysts Activation Energy o Induced fit: Substrate binding alters the
active site, increasing specificity
Enzymes as Catalysts Enzyme catalysis summarized in three steps: 1. Initiation: substrate moves into active site,
binds loosely
2. Transition state stabilization: transition state
fits the active site and is stabilized by it
3. Termination: reaction is complete, products
released from the active site
1
2
3
Enzymes as Catalysts pH and temperature o Each enzyme has an optimal pH and
temperature
Enzymes as Catalysts pH and temperature o Each enzyme has an optimal pH and
temperature
Enzymes as Catalysts Other requirements for enzymes o Prosthetic groups: permanently attached to
the enzyme (ion or organic)
o Co-Factors: temporarily attached to the
enzyme (ion)
o Coenzymes: molecule that is involved in the
reaction, but is regenerated after (organic)
Enzyme Regulation Enzymatic reactions are regulated o Competitive inhibitors: bind active site of
enzyme
o Can be reversible or irreversible
Enzyme Regulation Enzymatic reactions are regulated o Competitive inhibitors: bind active site of
enzyme ➢ Competes with substrate for binding
o Can be reversible or irreversible
Enzyme Regulation Enzymatic reactions are regulated o Non-competitive inhibitors: bind to another
part of the enzyme (not the active site)
o Can be reversible or irreversible
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
Reaction rate
rate by increasing substrate concentration
Substrate concentration
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
rate by increasing substrate concentration
Inhibitor more likely to bind
Substrate more likely to bind
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
rate by increasing substrate concentration
Increasing substrate concentration does not make any difference
Enzyme Regulation Allosteric Regulation o Allosteric = somewhere other than active site o Allosteric activators: bind somewhere other
than active site; increases binding of substrate
o Allosteric inhibitors: bind somewhere other
than the active site; decreases binding of substrate
Enzyme Regulation Enzyme regulation is important in metabolism
o If cell has lots of molecule X, it will “turn off”
the enzyme that makes molecule X
o Prevents wasting energy and resources
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. a) How would the activity of enzyme X under high temperatures compare to the activity of enzyme X under cold temperatures?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. b) If the gene coding for enzyme X is mutated and the enzyme is no longer able to bind inhibitor Y, how would this affect the activity of enzyme X under (i) high temperatures and (ii) low temperatures?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. c) Would increasing the concentration of the substrate for enzyme X increase its activity under cold temperatures? Why or why not?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. d) If inhibitor Y was a reversible, competitive inhibitor instead of an allosteric inhibitor, would increasing the concentration of the substrate increase the enzyme’s activity under cold temperatures? Why or why not?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. e) If inhibitor Y was a competitive, irreversible inhibitor instead of an allosteric inhibitor, would increasing the concentration of the substrate increase the enzyme’s activity under cold temperatures? Why or why not?
Lecture: ENZYMES Outline: 1. Reactions Catalysts o Activation energy o pH and temperature
o Other requirements for enzymes
2. Enzyme Regulation o Competitive inhibitors o Non-competitive inhibitors o Allosteric regulation
Enzymes as Catalysts Activation Energy o A spontaneous reaction (negative ∆G) may
be very, very slow
o Enzymes are catalysts increase the rate of
reactions by lowering the activation energy
o The reactants in an enzyme-catalyzed
reaction are called substrates
Enzymes as Catalysts Activation Energy o The substrate binds to the active site of the
enzyme
o The enzyme stabilizes the transition state by
tightly binding to it
Enzymes as Catalysts Activation Energy o The substrate binds to the active site of the
enzyme
o The enzyme stabilizes the transition state by
tightly binding to it
➢ An intermediate between the substrate
and the product energy of activation required to reach transition state
Enzymes as Catalysts Activation Energy o Induced fit: Substrate binding alters the
active site, increasing specificity
Enzymes as Catalysts Enzyme catalysis summarized in three steps: 1. Initiation: substrate moves into active site,
binds loosely
2. Transition state stabilization: transition state
fits the active site and is stabilized by it
3. Termination: reaction is complete, products
released from the active site
1
2
3
Enzymes as Catalysts pH and temperature o Each enzyme has an optimal pH and
temperature
Enzymes as Catalysts pH and temperature o Each enzyme has an optimal pH and
temperature
Enzymes as Catalysts Other requirements for enzymes o Prosthetic groups: permanently attached to
the enzyme (ion or organic)
o Co-Factors: temporarily attached to the
enzyme (ion)
o Coenzymes: molecule that is involved in the
reaction, but is regenerated after (organic)
Enzyme Regulation Enzymatic reactions are regulated o Competitive inhibitors: bind active site of
enzyme
o Can be reversible or irreversible
Enzyme Regulation Enzymatic reactions are regulated o Competitive inhibitors: bind active site of
enzyme ➢ Competes with substrate for binding
o Can be reversible or irreversible
Enzyme Regulation Enzymatic reactions are regulated o Non-competitive inhibitors: bind to another
part of the enzyme (not the active site)
o Can be reversible or irreversible
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
Reaction rate
rate by increasing substrate concentration
Substrate concentration
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
rate by increasing substrate concentration
Inhibitor more likely to bind
Substrate more likely to bind
Enzyme Regulation Competitive vs. Non-competitive Inhibitors o Competitive inhibitors: can out-compete
inhibitor by increasing substrate concentration
o Non-competitive inhibitors: cannot increase
rate by increasing substrate concentration
Increasing substrate concentration does not make any difference
Enzyme Regulation Allosteric Regulation o Allosteric = somewhere other than active site o Allosteric activators: bind somewhere other
than active site; increases binding of substrate
o Allosteric inhibitors: bind somewhere other
than the active site; decreases binding of substrate
Enzyme Regulation Enzyme regulation is important in metabolism
o If cell has lots of molecule X, it will “turn off”
the enzyme that makes molecule X
o Prevents wasting energy and resources
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. a) How would the activity of enzyme X under high temperatures compare to the activity of enzyme X under cold temperatures?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. b) If the gene coding for enzyme X is mutated and the enzyme is no longer able to bind inhibitor Y, how would this affect the activity of enzyme X under (i) high temperatures and (ii) low temperatures?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. c) Would increasing the concentration of the substrate for enzyme X increase its activity under cold temperatures? Why or why not?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. d) If inhibitor Y was a reversible, competitive inhibitor instead of an allosteric inhibitor, would increasing the concentration of the substrate increase the enzyme’s activity under cold temperatures? Why or why not?
Enzyme Regulation Enzyme X is allosterically regulated by inhibitor Y. Inhibitor Y is present in high concentrations when the cell is under cold temperatures. e) If inhibitor Y was a competitive, irreversible inhibitor instead of an allosteric inhibitor, would increasing the concentration of the substrate increase the enzyme’s activity under cold temperatures? Why or why not?
