Write the scientific term. Lesson (4) Chemical reactions inside organisms' bodies

1- Polar molecule

2- Hydrogen bonds

3- Specific heat

4- Surface tension

Lesson (4) Chemical reactions inside organisms' bodies

Biological chemical reactions occur inside living organisms body in order to help in growth, get energy, build tissues and sustain life. These reactions are called " Metabolism". If these reactions stop in a living organism, it will die.

Metabolism: A group of biochemical reactions which occur within living organisms in order to build complex macromolecules from simple molecules, or break up molecules to get energy.

Metabolism reactions are divided into:-

1- Anabolism

2- Catabolism

Anabolism: A process by which simple molecules are used to build complex macromolecules through a group of chemical reactions which consume energy.

à Building proteins from amino acids is an example on anabolism

Catabolism: A process by which energy is being released from the chemical bonds in some molecules such as glucose.

à Cells break up glucose to release energy from it.

à Chemical reactions generally need high activation energy to occur. To decrease the energy used by cell in biochemical reactions occurring inside it, we need catalysts to decrease activation energy needed for the reaction to occur, which speeds this reaction up. Such catalysts are called enzymes

Activation energy: The minimum energy required for a chemical reaction to occur.

(For reading only): The term activation energy was coined by Swedish scientist Arrhenius in 1889 A.D.

Enzymes: Biological catalysts formed from proteins molecules which speed up chemical reactions occurring within living organisms.

Enzymes are formed from groups of amino acids which are arranged in the form of polypeptide chains which forms the stereoisomerism of enzymes.

(For illustration) stereoisomer: Molecules that have the same no. of atoms but with different arrangements.

The properties of enzymes

1- They resemble chemical catalysts, as they only speed up the chemical reaction without taking part in it.

2- Enzymes are affected by the concentration of hydrogen ions (pH) and temperature.

3- Enzymes are different from other catalysts because every enzyme is specialized for only one reactant substance (called substrate) and a small no. of reactions.

4- Enzymes decrease the activation energy needed for chemical reactions to occur.

Substrate: The substance on which enzyme work.

Enzymes are classified according to their chemical structure into:-

Simple enzymes

They are enzymes which are composed of simple proteins.

Example: Amylase enzyme.

(For reading only) amylase is an enzyme secreted by salivary glands, which changes starch into sugar.

Complex enzymes

They are enzymes which consist of:-

1- Protein part

2- Non protein part: This part may be an atom of metal (iron, copper, magnesium) or an organic molecular called coenzyme, non protein part is the active site of enzyme molecule.

Example: Catalase enzyme

(For reading only) catalase enzymes speeds up the decomposition of hydrogen peroxide H2O2 into water and oxygen

The active site of enzyme

Every enzyme has one or more active sites

Active site: A stereoisomer which is responsible for enzyme work

1- The active site of an enzyme (E) links with the substrate (S) forming enzyme-substrate complex (ES).

2- The complex decomposes, products of reaction are formed and the enzyme gets released.

Fig. (12) The mechanism of enzyme

Temperature

Every enzyme has a different optimum temperature (the temperature on which the enzyme becomes most active).

à When the temp. of an enzyme increases more than its optimum temperature, its activity decreases gradually until it stops due to the change of its structure.

à When the temp. of an enzyme becomes less than its optimum temperature, its activity also decreases gradually. Enzyme activity stops at 0◦C (but it become active again when its temperature increases).

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