Enzymes An 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? An enzyme is catalytic protein, which is a chemical agent that changes the rate of reaction without being consumed. affected by some factors They speed up chemical reactions. they’re substrate specific. They have (the active site).

Frist: speeding up chemical reactions e.g. hydrolyzing sucrose Sucrose Glucose+ Fructose H2OH2O H2OH2O This process needs Energy This process needs Energy

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 E A. The transition state can then be reached even at 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.

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

Catalytic cycle of an enzyme

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 bonds After breaking the bonds

Factors Affecting Enzyme Activity temperature PH COFACTORS

Factors Affecting Enzyme Activity Increasing the temperature Make the reaction faster But in certain range Or denature the reaction above range exceptions 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. Inorganic e.g. Zinc, iron and copper Organic e.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.

PLZ OPEN THE VIDEO Enzyme function and inhibition (with audio narration)

PLZ OPEN THE VIDEO how enzymes work

PLZ OPEN THE VIDEO What are enzymes

PLZ OPEN THE VIDEO Enzyme

PLZ OPEN THE VIDEO الإيدز HIV

- 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 reaction c)- 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 reaction c)- 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 E A b- Increasing E A c- Stabilizing E A