Chemical Compost Ion of the Cell (Enzyme)

8/8/2019 Chemical Compost Ion of the Cell (Enzyme)

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ENZYMES

Proteins which act asbiological catalysts.

Speed upbiochemical reactions remainunchanged at the end of reaction.


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Mechanism of Enzyme

CatalysisWhat is a catalyst?

React in the enzyme-catalysed reactionsare called substrate.

Produced at the end of reactions arecalled products.

It participates in reactions but is neither achemical reactant nor chemical product.

S + C (catalyst) P + C (catalyst)

S P


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Thousands of simultaneous

biochemical reactions occur inliving cells.

Called metabolism.

Metabolism includes bothanabolism and catabolism.


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Anabolism biosynthesis of

complex compounds fromsimpler substances, ex:

photosynthesis.

Catabolism breakdown ofcomplex substances into

simpler ones, ex:

decomposition.


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General characteristics

of enzymesSpeed up the rate of

biochemical reactions.

Not destroyed by the reactions

they catalysed.

Effective in small amount.

Can work in either direction

reversible.

Lactose + water Glucose + galactose

lactase


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General characteristics

of enzymesDenatured by high temperatures

(above 40C).

Sensitive to pH.

Extremely specific.

Activity is affected by

inhibitors.

Some enzymes require

cofactors.


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Lock and Key Hypothesis

Each enzyme molecule has a

region with a very precise

shape active site.

The substrate molecule fits into

the active site like a key into a

lock. Form enzyme-substrate

complex.


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Lock and Key Hypothesis

The enzyme then changes the

substrate either by splitting it

apart (hydrolysis) or linkingthem together(condensation).

Once formed, the product no

longer fit into the active site.


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Lets watch the

animation!


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LE 8-16

Substrate

Active site

Enzyme Enzyme-substratecomplex


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Enzyme-substrate

complex

Substrates

Enzyme

Products

Substrates enter active site; enzyme

changes shape so its active site

embraces the substrates (induced fit).

Substrates held in

active site by weak

interactions, such as

hydrogen bonds and

ionic bonds.

Active site (and R groups of

its amino acids) can lower EAand speed up a reaction by

acting as a template for

substrate orientation,

stressing the substrates

and stabilizing the

transition state,

providing a favorablemicroenvironment,

participating directly in the

catalytic reaction.

Substrates are

converted into

products.

Products are

released.

Active

site is

available

for two new

substrate

molecules.

Chemical Compost Ion of the Cell (Enzyme)

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