Chemical Basis of Life

Atom:

nucleus

electrons (-) charged

neutrons (no charge)

protons (+ charged)

energy levels

[The structure of an atom]

Atoms are the basic building blocks of matter. They cannot be subdivided any further by any ordinary chemical means.

Element: Elements are made up of only one kind of atom. e.g. Iron (Fe), Oxygen (O), diamond, Neon (Ne)

Compound: Two or more kinds of atoms are combined in definite proportions. e.g. H2O, CO2, glass

2H O C 2O

Basic Components of Living Things

Inorganic Molecules

• Water• Acids, Bases and

Salts• Minerals

Organic Molecules• Carbohydrates• Lipids• Proteins• Vitamins• Nucleic Acids• ATP

WATER

Water is a polar molecule.

H partially negative - O + partially positive

H

WATER

Hydrogen Bonds in Water

WATERProperties of water

CohesionIt is the force of attraction between the molecules of the same substance. Ex: Water molecules are attached to each other with cohesion forces.

AdhesionIt is the force of attraction between the molecules of two different substances. Ex: Water molecules can dissolve most polar substances.

WATERProperties of water

Cohesion Adhesion

WATER

WATER Water is good solvent.

Water is the medium of transport for foods, minerals and other substances in living systems.

The harmful substances formed by metabolic activities are removed from body by water.

Water is essential for biochemical reactions.

Water is transparent that makes penetration of light possible into deep water.

Many organisms can only use oxygen dissoved in water; therefore they live in water.

The density of water is maximum at 4°C. So water at 4°C moves downward and exchanges heat with surrounding water. This helps deep sea water have fairly narrow temperature change.

Below 0°C, hydrogen bonds can’t break, and they lock water molecules in the bonding pattern of ice. During winter freezes, ice sheets form on ponds, lakes and streams. They hold in water’s heat and help protect aquatic organisms from freezing.

WATER

Water is a great molecule by means of temperature stabilization. When water is liquid, its hydrogen bonds are constantly breaking and forming again. With enough heat energy, hydrogen bonds stay broken and molecules at the water’s surface escape into the air. This is called evaporation. Because water has a very high specific heat molecules take away energy when they leave the surface and lower the temperature. This is the reason why we cool off when we sweat.

WATER

Acids and Bases:

Acids: An acid is any compound that produces hydrogen ions in solution. When acids are dissolved in water, the hydrogen breaks lose a hydrogen ion (H+).

• Acids are sour in taste.

Examples: lemon, apple, vinegar, tomato, grapefruit.

HCl H+ + Cl

H2SO4 2H++SO4-2

Bases: A base is a compound that produces hydroxide (hydroxyl) ions when dissolved in water.

• Bases are bitter in taste.

Examples: sea water, ammonia water, soap

NaOH Na + OH-

NH3 + H2O NH4 + OH-

Neutral substances: Any chemical that contains equal amounts of H+ and OH- ions are said to be neutral.

Ex: H2O H+ + OH-

ACIDS• Have sour taste• Turn blue litmus

paper’s color into red• HCl and H2SO4 are

strong acids• Acetic acid and citric

acid are weak

BASES• Have bitter taste• Turn red litmus

paper’s color into blue• Organic bases

generally have C and N

• NaOH, KOH are example of bases

The pH Scale:

The H+ concentration is indicated by a unit of measure called pH. The pH scale has been set up in such a way that;

• high concentrations of H+ have a low pH,

• low concentrations of H+ have high pH values.

0 7 14

[H+] > [OH-] [H+] = [OH-] [H+] < [OH-]

Acidic BasicNeutral

Any chemical that has different colors in acids and in bases is called indicator.

Litmus paper

pH paper

Methyl orange

Phenolphtalein

Blue; turns red in acidic solution

Red; turns blue in basic solution

gives exact pH value

changes from yellow to red in acidic solutions

changes from colorless to red (pink) in basic solutions

Acid and Base Indicators

Buffers:

Chemical reactions are very sensitive to even slight shifts in pH. Maintaining the pH balance of blood and tissue fluid is very important.

The addition and removal of H+ ions has to be controlled continuously in order to protect the stable internal environment of the body.

A buffer is any molecule that can combine with H+ ions, release them or both, and so help stabilize pH.

HCO3- + H+ H2CO3

Neutralization: When solutions of an acid and a base are mixed, a reaction takes place. The hydrogen ions from the acid combine with the hydroxide ions from the base to form water.

(acid) (base) (salt) (water)

HCl + NaOH NaCl + HOH

The ionic compound produced by the neutralization reaction between an acid and a base is called a salt.

Chemical Compounds in Living Things

What are the most abundant elements in living things? Hydrogen Nitrogen

Oxygen Carbon

Less frequently the elements Phosphorus (P), Sulfur (S), Iron (Fe), Calcium (Ca), Sodium (Na), Chlorine (Cl), Magnesium (Mg), and Potassium (K) are found in organic compounds.

Chemical Compounds

Organic Compounds

Inorganic Compounds contain C (carbon)

atoms

also contain H (hydrogen) and O (oxygen) atoms

Ex: carbohydrates, lipids, proteins, vitamins, ATP, nucleic acids

do not contain C (carbon) atoms

exceptions: CO2, CaCO3

(although they contain C atoms these are inorganic compounds because they do not contain H)

Ex: H2O, minerals

Why carbon is so special?It is the unique element which have the ability to form covalent bonds that are strong and stable.

C has 6 electrons: -2 of them are in the first energy level, -the other 4 electrons are in the second energy level.

For this reason carbon can take 4 electrons that means carbon can form 4 single covalent bonds.

first energy level

second energy level

Carbon Atom

H H

H

H

C

Methane Molecule (CH4)