Jenny's Notes
10/25/04
Chapter 6 Notes Continued
-The three dimensional structures of enzymes (almost all proteins)
-Changes in shape influence reaction rate
-Some conditions lead to the most active conformation and lead up to optimal rate of reaction
*Include in essay- control group, variable, short procedure, substrate, enzyme name*
Quantifiable procedure- quantify ph of a solution- determine what pH it is
Qualifiable- means is it acidic or basic (for pH)
Because pH also influences shape and therefore reaction rate, each enzyme has an optimal pH too
Falls between 6-8 for most enzymes
Digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 8 both matching their working environment
Many enzymes require non-protein helpers, cofactors for catalytic activity
They bind permanently to the enzyme or reversibly
Some inorganic cofactors include: zinc, iron, and copper
Organic cofactors, coenzymes include vitamins or molecules derived from vitamins
The manners by which cofactors assist catalysis is diverse
Binding by some molecules, inhibitors, prevent enzymes from catalyzing reactions
If binding involves covalent bonds, then inhibition is often irreversible
If binding is weak, inhibition may be reversible
If the inhibitor binds to the same site as the substrate it blocks the substrate and is a competitive inhibitor
If the inhibitor binds somewhere other than the active site, it blocks substrate binding via noncompetitive inhibition
Binding by the inhibitor causes the enzyme to change shape, rendering the active site unreceptive at worst or less effective at catalyzing the reaction
Reversible inhibition of enzymes is a natural part of the regulation of metabolism
In many cases the molecules that naturally regulate enzyme activity behave like reversible noncompetitive inhibitors
These molecules often bind weakly to an allosteric site, a specific receptor on the enzyme that is not the active site
Binding by these molecules can either inhibit or stimulate enzyme activity
Most allosterically regulated enzymes are constructed of two or more polypeptide chains
Each subunit has it’s own active sites and allosteric sites are often located where subunits join
In many cases both inhibitors and activators are similar enough in shape that they compete for the same allosteric for the same allosteric sites
These molecules may be products and substrates of a metabolic pathway
One of the common methods of metabolic control is feedback inhibition in which a metabolic pathway is turned off by its end product
The end product acts as an inhibitor of an enzyme in the pathway
When the product is abundant is abundant the pathway is turned off, when rare the pathway is active
In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called cooperativity
This mechanism amplifies the response of enzyme to substrates, priming the enzyme to accept additional substrates
Enzyme regulation- feedback inhibition, cooperativity
Chapter 6 Notes Continued
-The three dimensional structures of enzymes (almost all proteins)
-Changes in shape influence reaction rate
-Some conditions lead to the most active conformation and lead up to optimal rate of reaction
*Include in essay- control group, variable, short procedure, substrate, enzyme name*
Quantifiable procedure- quantify ph of a solution- determine what pH it is
Qualifiable- means is it acidic or basic (for pH)
Because pH also influences shape and therefore reaction rate, each enzyme has an optimal pH too
Falls between 6-8 for most enzymes
Digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 8 both matching their working environment
Many enzymes require non-protein helpers, cofactors for catalytic activity
They bind permanently to the enzyme or reversibly
Some inorganic cofactors include: zinc, iron, and copper
Organic cofactors, coenzymes include vitamins or molecules derived from vitamins
The manners by which cofactors assist catalysis is diverse
Binding by some molecules, inhibitors, prevent enzymes from catalyzing reactions
If binding involves covalent bonds, then inhibition is often irreversible
If binding is weak, inhibition may be reversible
If the inhibitor binds to the same site as the substrate it blocks the substrate and is a competitive inhibitor
If the inhibitor binds somewhere other than the active site, it blocks substrate binding via noncompetitive inhibition
Binding by the inhibitor causes the enzyme to change shape, rendering the active site unreceptive at worst or less effective at catalyzing the reaction
Reversible inhibition of enzymes is a natural part of the regulation of metabolism
In many cases the molecules that naturally regulate enzyme activity behave like reversible noncompetitive inhibitors
These molecules often bind weakly to an allosteric site, a specific receptor on the enzyme that is not the active site
Binding by these molecules can either inhibit or stimulate enzyme activity
Most allosterically regulated enzymes are constructed of two or more polypeptide chains
Each subunit has it’s own active sites and allosteric sites are often located where subunits join
In many cases both inhibitors and activators are similar enough in shape that they compete for the same allosteric for the same allosteric sites
These molecules may be products and substrates of a metabolic pathway
One of the common methods of metabolic control is feedback inhibition in which a metabolic pathway is turned off by its end product
The end product acts as an inhibitor of an enzyme in the pathway
When the product is abundant is abundant the pathway is turned off, when rare the pathway is active
In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called cooperativity
This mechanism amplifies the response of enzyme to substrates, priming the enzyme to accept additional substrates
Enzyme regulation- feedback inhibition, cooperativity