EnzymesAn introduction to metabolism

The purpose of an enzyme in a cell is to allow the cell to carry out chemical reactions very quickly. These reactions allow the cell to

build things or take things apart as needed. This is how a cell grows and reproduces.

What are enzymes?

affected by some factorsThey speed up

chemical reactions.

they’re substrate specific.

They have (the active

site).

Frist: speeding up chemical reactionse.g. hydrolyzing sucrose

H2O

H2O

Activation energy

It’s the amount of energy necessary to push the reactants over an energy barrier.

The energy barrier

Amount of energy

reactants need to reach the products( without the enzyme )

Energy barrier and amount of

energy needed after the enzyme

Delta G

Enzymes in metabolic reactions

Enzyme speed reactions by lowering EEnzyme speed reactions by lowering EAA. The transition . The transition

state can then be reached even at state can then be reached even at moderate temperatures. moderate temperatures.

Substrate specific

This means that every enzyme is specific for a certain substance called the substrate. The enzyme can only identify its substrate and work on it.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

Second: enzymes are substrate specific

A Substrate is a reactant which binds to an enzyme.

e.g. Sucrose (substrate) Glucose + Fructose

Catalyst(Enzyme)

products

Each enzyme works with certain substrate

(due to its active site)

Third: the active site

Gives the enzymes its specificity due to the fit that attracts the substrate.

The enzyme changes shape and bring the chemical groups in position

The cycle in which the enzyme attracts the substrate to the active site and then produce the products

Catalytic cycle of

the enzyme

Weak hydrogen bondsAfter breaking the bonds

Factors Affecting Enzyme Activity

Factors Affecting Enzyme Activity

Make the reaction fasterBut in certain

rangeOr denature the reaction above range

Digestive enzymes work best at PH 2

intestine enzymes work best at PH 8

Other factors

Cofactors

Non-protein helpers.

Attach permanently to the enzyme

They are two types:

Inhibitors

They prevent enzymes from catalyzing.

The inhibition could be irreversible (when covalently bind) or reversible (when binding weakly)

There are two types of inhibitors.

Inorganice.g.

Zinc, iron and copper

Organice.g.

vitamins

Types of inhibitors

They bind to the same site as the substrate

They block the active site.

They bind somewhere other than the active site.

They change the enzyme shape and deactivate the active site.

Conclusions

What we know about enzymes

A single enzyme can catalyze 1000s of reactions in seconds.

Enzymes are reusable. Most of them catalyze reactions in both ways. They are affected by reactant concentration:

A. The concentration directs the reaction to equilibrium.

B. Some concentration cause enzyme saturation.

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Q1: Write whether each of the following statements is True (T) or False (F):

1-The non-competitive inhibitor reduces the activity of an enzyme by changing the shape of the

enzyme………………………………………………………………………………2-The activity of an enzyme is affected by

temperature and pH.3- Enzymes are substrate-specific …

4-The active site of enzyme is the region at which the competitive inhibitor is bound

5- The changes in temperature will not affect the activity of enzymes.

Q 2: Choose the correct answer (one answer only): Which of the following is true about enzymes:

a)- decrease the free energy change of a reaction b)- increase the rate of the

reactionc)- change the direction of the reaction

d)- are altered by the reactions they catalyse

2-The non-competitive inhibitor inhibits the enzyme activity by:

a)- binding at the active site of the enzyme b)- changing the shape of the enzyme

c)- changing the free energy of the reaction d)- acting as a co-enzyme

 3-The active site of the enzyme is the region that:

a)- binds allosteric regulators of the enzyme b)- binds to the substrate and involved

in the catalytic reactionc)- binds the products of the catalytic reaction d)- is inhibited by the presence of a co-

enzyme or a co-factor 

4-All of the following are factors that affect enzyme activity except:

a)- temperature b)- cofactors c)- pH d)- ADP

 5-- Enzymes work by

a- Decreasing EA b- Increasing EA c- Stabilizing EA