lecture 10-2 enzymes
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Lecture 10-2 Enzymes. Enzymes. Biological catalysts Lower the activation energy, increase the speed of a reaction (millions of reactions per minute!). How Enzymes Work. Enzymes = large protein molecules that function as biological catalysts. - PowerPoint PPT PresentationTRANSCRIPT
Lecture 10-2Enzymes
Enzymes
• Biological catalysts– Lower the activation energy, increase the speed of
a reaction (millions of reactions per minute!)
Enzymes = large protein molecules that function as biological catalysts.Catalyst = chemical that speeds up a reaction
without being consumedNOTE: enzyme names end in –ase and are
often named after their substratesThe enzyme that hydrolyzes sucrose is sucraseHydrolases, Add water during Hydrolysis
reactions
How Enzymes Work
Energy of activation(Ea)
• There is an energy barrier that must be overcome before a chemical reaction can begin. This is called The energy of activation• Enzymes speed up the reaction by lowering
the Ea barrier
How Enzymes Work
• Energy of Activation– Enzymes lower the barrier– Eg.Mexican jumping bean
How Enzymes Work
The effect of an enzyme on the energy of activation
Figure 2.20
Activationenergy required
Less activationenergy required
WITHOUT ENZYME WITH ENZYME
Reactants
Product Product
Reactants
PLAY Animation: Enzymes
How Enzymes Work
Enzymes
Very selective3D shape that determines its specificity for a
substrateSubstrate = the substance that the enzyme works
onSubstrate binds to the enzyme in the active site
Pocket or groove on protein surface where binding occurs
Enzyme action
Three basic steps involves in enzyme action: 1) The enzyme active site binds to the
substrate. 2)The enzyme –substrate complex undergoes
internal rearrangement that form the product. 3)The enzyme releases the the product of the reaction.
How Enzymes Work
Figure 2.21
Substrates (S)e.g., amino acids
Enzyme (E)Enzyme-substratecomplex (E-S)
Enzyme (E)
Product (P)e.g., dipeptide
Energy isabsorbed;bond isformed.
Water isreleased.
Peptidebond
Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.
Internalrearrangementsleading tocatalysis occur.
Product isreleased. Enzymereturns to originalshape and isavailable to catalyzeanother reaction.
Active site
+ H2O
1 23
Figure 2.21, step 1
Substrates (S)e.g., amino acids
Enzyme (E)Enzyme-substratecomplex (E-S)
Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.
Active site
+
1
Figure 2.21, step 2
Substrates (S)e.g., amino acids
Enzyme (E)Enzyme-substratecomplex (E-S)
Energy isabsorbed;bond isformed.
Water isreleased.
Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.
Internalrearrangementsleading tocatalysis occur.
Active site
+ H2O
1 2
Figure 2.21, step 3
Substrates (S)e.g., amino acids
Enzyme (E)Enzyme-substratecomplex (E-S)
Enzyme (E)
Product (P)e.g., dipeptide
Energy isabsorbed;bond isformed.
Water isreleased.
Peptidebond
Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.
Internalrearrangementsleading tocatalysis occur.
Product isreleased. Enzymereturns to originalshape and isavailable to catalyzeanother reaction.
Active site
+ H2O
1 23
Characteristics of Enzymes
• Often named for the reaction they catalyze; usually end in -ase (e.g., hydrolases, oxidases)
• Some enzymes are purely protein.• Some functional enzymes (holoenzymes)
consist of two parts: – Apoenzyme (protein) – Cofactor (metal ion) or coenzyme (a vitamin)
• Cofactors– Nonprotein helpers• May be inorganic substances
– Zinc, iron or copper– Magnesium is a cofactor essential for proper functioning
of chlorophyll
• Coenzymes – Organic helpers• Vitamins
– Vitamin B6 is used to convert one amino acid to another
Characteristics of Enzymes
• Enzyme activity is affected by its
environment– Temperature affects molecular motion• Enzyme’s optimal temperature is when there is the
highest rate of contact between the enzyme and substrate• Temperature too high – denaturation
– Changes the shape and the function of the enzyme– Salt concentration• Salt interferes with some of the chemical bonds
that maintain protein shape– pH • Same is true for pH outside of the 6-8
range.eg.digestive enzyme produce in pancreas are activated in small intestine.
Characteristics of Enzymes
• Sometimes enzymes are inactivated immediately after they have performed .eg.
blood clot formation.
Thank you