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.

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Lecture 10-2 Enzymes

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Lecture 10 2 enzymes

Lecture 10-2Enzymes


Enzymes

Enzymes

  • Biological catalysts

    • Lower the activation energy, increase the speed of a reaction (millions of reactions per minute!)


Lecture 10 2 enzymes

How Enzymes Work

  • Enzymes = large protein molecules that function as biological catalysts.

    • Catalyst = chemical that speeds up a reaction without being consumed

    • NOTE: enzyme names end in –ase and are often named after their substrates

      • The enzyme that hydrolyzes sucrose is sucrase

      • Hydrolases, Add water during Hydrolysis reactions


Energy of activation ea

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


Lecture 10 2 enzymes

How Enzymes Work

  • Energy of Activation

    • Enzymes lower the barrier

    • Eg.Mexican jumping bean


Lecture 10 2 enzymes

How Enzymes Work

The effect of an enzyme on the energy of activation


Lecture 10 2 enzymes

WITHOUT ENZYME

WITH ENZYME

Activation

energy

required

Less activation

energy required

Reactants

Reactants

Product

Product

PLAY

Animation: Enzymes

Figure 2.20


Lecture 10 2 enzymes

How Enzymes Work

  • Enzymes

    • Very selective

    • 3D shape that determines its specificity for a substrate

      • Substrate = the substance that the enzyme works on

    • Substrate binds to the enzyme in the active site

      • Pocket or groove on protein surface where binding occurs


Enzyme action

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.


Lecture 10 2 enzymes

How Enzymes Work


Lecture 10 2 enzymes

Product (P)e.g., dipeptide

Substrates (S)e.g., amino acids

Energy isabsorbed;bond isformed.

Water isreleased.

Peptidebond

+

H2O

Active site

Enzyme-substratecomplex (E-S)

Enzyme (E)

Enzyme (E)

1

2

Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.

Internalrearrangementsleading tocatalysis occur.

3

Product isreleased. Enzymereturns to originalshape and isavailable to catalyzeanother reaction.

Figure 2.21


Lecture 10 2 enzymes

Substrates (S)e.g., amino acids

+

Active site

Enzyme-substratecomplex (E-S)

Enzyme (E)

1

Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.

Figure 2.21, step 1


Lecture 10 2 enzymes

Substrates (S)e.g., amino acids

Energy isabsorbed;bond isformed.

Water isreleased.

+

H2O

Active site

Enzyme-substratecomplex (E-S)

Enzyme (E)

1

2

Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.

Internalrearrangementsleading tocatalysis occur.

Figure 2.21, step 2


Lecture 10 2 enzymes

Product (P)e.g., dipeptide

Substrates (S)e.g., amino acids

Energy isabsorbed;bond isformed.

Water isreleased.

Peptidebond

+

H2O

Active site

Enzyme-substratecomplex (E-S)

Enzyme (E)

Enzyme (E)

1

2

Substrates bindat active site.Enzyme changesshape to holdsubstrates inproper position.

Internalrearrangementsleading tocatalysis occur.

3

Product isreleased. Enzymereturns to originalshape and isavailable to catalyzeanother reaction.

Figure 2.21, step 3


Characteristics of enzymes

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)


Lecture 10 2 enzymes

Characteristics of Enzymes

  • 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


Lecture 10 2 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 enzymes1

Characteristics of Enzymes

  • Sometimes enzymes are inactivated immediately after they have performed .eg.

    blood clot formation.


Thank you

Thank you


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