Write the scientific term

1- Proteins

2- Peptide bond

3- Dipeptide chain

4- Polypeptide chain

5- Nucleic acids

6- Casein proteins

7- Simple proteins

8- Associated proteins

9- Hemoglobin

10- Nucleotides

11- Ribose

12- Deoxyribose

13- DNA

14- RNA

Lesson (3) Water

à Water is the basis of life on our planet, it exists in different physical states (solid, liquid, gas). Water makes up:-

à 70% of the surface of earth

à (65% - 90%) of the weight of living organisms

The importance of water

It plays an important role in all vital processes within living organisms.

The molecular structure of water

àwater molecule H2O is composed of one oxygen atom and two hydrogen ones, these atoms are bound covalently (by covalent bond).

àIn water molecule, hydrogen carries molecular negative charge, while oxygen carries molecular positive charge. Thus, water molecule is polar molecule because it has positive and negative poles.

Fig. (10) The molecular structure of water

à Close water molecules are attracted to each other by relatively low electric attraction (as negative hydrogen atoms attract positive oxygen atoms in another molecules). This bond is called Hydrogen bond

Fig. (11) Hydrogen bond diagram

à Water has unique properties because of its polarity and hydrogen bonds between its molecules

Water is a polar solvent

Water is from the best solvents and regarded as "the general solvent" due to the polarity of its molecules

Example:-

When sodium chloride NaCl dissolves in water, it produced positive sodium ions and negative chlorine ions. Thus, positive oxygen atoms of water attract negative chlorine ions, and negative hydrogen atoms attract positive sodium ions.

à All polar substances (substances containing ions) can dissolve in polar solvents such as water

Дата добавления: 2015-10-23